Air Heaters

Max. Operating Typical Max.

Temperatures Watt Densities
Air Heaters Sheath Materials °F °C W/in2 W/cm2 Page
Duct Heaters
LDH SERIES and D SERIES Alloy 840 1200 650 30 4.7 375

MDH SERIES Alloy 840 1200 650 26 4.0 389

Finned
375 Finned Strip Aluminized steel 1100 595 33 5.1 393
FINBAR™ Single-Ended 304 stainless steel 1200 650 50 7.7 399
FIREROD® Cartridge Alloy 800 Application Specific 100 15.5 400
Enclosure Heaters
WATROD™ Alloy 840 390 200 15 2.3 401
Silicone Rubber Fiberglass reinforced 500 260 5 0.8 403
silicone rubber
FLUENT® In-line 444 stainless steel 482 250 150 23 406
(substrate tube), (internal)
316L stainless steel
(baffle and fittings)

Air Heaters

373
374
Air Heaters
Duct Heaters
LDH SERIES and D SERIES
Constructed of sturdy 0.430 in. (11 mm) diameter
WATROD™ heating elements mounted to a 1/4 in.
(6 mm) thick steel flange, duct heaters are easily
adapted to many non-pressurized air-heating systems.
They are easily installed in applications requiring a wide LDH SERIES
range of temperature versus air flow combinations.
The modular duct heater offers increased reliability. The
individual modules are removable through the housing of
the assembly, which eliminates the need to pull the
complete heater from the duct work. This reduces
downtime costs because the heating elements can be
replaced individually. Performance improvements include
quicker response time and reduced infiltration from the air
stream being heated into the electrical enclosure.
Watlow® duct heaters offer advantages over gas or oil D SERIES
fired and open coil electric units with:
• Installation flexibility—no flues or fuel lines
• 100 percent energy efficient—no energy loss up
the flue Threaded
Bussing Hole
• Universal availability of electricity
• Resistance coil in sheath is protected from corrosive
environments
Performance Capabilities Mineral
Insulation
• Watt densities up to 40 W/in2
(6.2 W/cm2)
• Recommended process temperatures from Single
Screw
-20 to 1200°F (-29 to 650°C) Clamp

• Catalog P/N wattages up to 225kW 1/4 in. (6 mm) inside diameter thermowell
• Voltages up to 600VAC • Accepts an optional Type J or K thermocouple for
Features and Benefits accurate sheath temperature sensing (D SERIES only)
Long life alloy 840 sheath Rigid stainless steel supports
• Resists corrosion/oxidation while protecting resistance • Prevents element sagging or deformation in various
coils against contamination mounting positions
1/4 in. (6 mm) thick steel flange with 3/8 in. (9.5 mm)
MgO insulation filled elements compacted to rock
diameter mounting holes
hard density
• Easily bolts to the duct wall
• Maximizes dielectric strength, heat transfer and life
WATROD hairpins are repressed (recompacted)
Field replaceable heating elements
after bending to assure MgO density
• Permits easy service and reduces downtime. Element
• Eliminates hot spots and electrical insulation voids
change-out is made simple by a single screw clamp
(D SERIES only) Stock heaters feature from three to 60 elements
1 • Meets a wide variety of kilowatt demands
3 /2 in. (90 mm) thick mineral insulation
• Keeps wiring cooler and reduces heat loss One or three phase voltages
• Meets local power supplies
Silicone resin seals rated to 221°F (105°C)
• Protects elements against moisture and other Maximum 48 amperes per circuit
• Complies with National Electrical Code (NEC)
contaminants
Duct heaters with general purpose enclosures
General purpose terminal enclosure
meet UL® and CSA component recognition to 480
• Offers easy access to wiring
and 600VAC maximum respectively—UL® and CSA
file numbers are E52951 and 31388

375
Air Heaters
Duct Heaters
LDH SERIES and D SERIES
Typical Applications Required Application Information
• Drying ovens • Desired outlet air temperature
• Autoclaves • Inlet air temperature
• Furnaces • Delta T—the temperature difference between inlet and
• Load banks desired outlet temperature
• Heat treating • Air volume (CFM/CMM) measured at both inlet
temperature and pressure
• Reheating
• HVAC • Air velocity in feet per minute (FPM); meters per minute
(MPM) which equals:
• Paint drying
English
Choosing a Duct Heater CFM measured at standard conditions
FPM =
The English and metric graphs, shown on the following Duct cross section area at heater in ft2
pages, will help you to select the correct duct heater. Metric
These graphs include: Watt Density vs. Air Temperature/ CMM measured at normal conditions
MPM =
Velocity, Watt Density vs. Sheath Temperature and Duct cross section area at heater in m2
Pressure Drop vs. Air Velocity.
These graphs, with the quick formulas on this page,
along with information specific to your application, • Minimum duct heater wattage (kW). This can be
will determine the correct duct heater specifications. determined by:
However, if engineering assistance is needed, contact
English
your Watlow representative.
CFM x Delta T (°F) x 1.1 (safety factor)
kW =
3000
Metric
CMM x Delta T (°C) x 1.1 (safety factor)
kW =
48

Note: The duct heater, or combination of duct heaters,

used for the process should be equal to or exceed the
minimum wattage calculation.

376
 Air Heaters
Duct Heaters
LDH SERIES and D SERIES
Watt Density vs. Air Temperature/Velocity
To decide watt density requirements, first determine curve’s intersecting point. This shows the recommended
the desired outlet air temperature and velocity in feet watt density based on a maximum sheath temperature
per minute. Then, follow the lines on the graph for of 1400°F (760°C). For longer heater life, lower watt
velocity and process temperature to the watt density densities should be chosen.

WATROD Duct Heater WATROD Duct Heater

Watt Density Vs. Air Temperature Velocity Watt Density Vs. Air Temperature Velocity
1600 500
/in 2

/in 2

in 2
in 2

/in 2

/in 2
1500

m2

m2

cm 2
2

m2

m2
/cm
W/
W/

/c

/c
W

W/c

W/c
W

8W
1400

W/
W

5W

W
40

30

20
23

16

6.2

3.1
3.5
1300 400

2.5

1.25
4.6
1200
1100

Air Velocity—MPM
s

s
Air Velocity—FPM

er

er

s
1000

er

er
at

at

300

at

at
He

He

900

He

He
ct

ct

ct

ct
Du

800
Du

Du

Du
g

log

g
lo

700

log
lo
ta

200
ta

ta
Ca

ta
Ca

600

Ca

Ca
500

400
100
300
200
100

100 200 300 400 500 600 700

100 200 300 400 500 600 700 800 900 1000 1100 1200
Process Temperature—°C
Process Temperature—°F
Estimated Sheath Temperature = 760°C
Estimated Sheath Temperature = 1400°F

Watt Density vs. Sheath Temperature

The Watt Density vs. Sheath Temperature graph shows WATROD Duct Heater
the air velocity (FPM or MPM) required to operate a Watt Density Vs. Sheath Temperature
10
WATROD duct heater at specific watt densities or sheath
9
temperatures. Also depicted is the appropriate watt Inlet Temperature at 25°C
density vs. sheath temperature at a specified air flow. 8

7
Watt Density—W/cm2

PM PM
PM

PM

WATROD Duct Heater 6 M M

M

5 0
Watt Density Vs. Sheath Temperature 23 18
5

5
47

36

60
5
56
PM
Inlet Temperature at 4 M
52
75°F 90
48
3 tion
vec
44 Con
M PM at ural
40 PM PM FP F
2 or N
Watt Density—W/in2

F F 0 0 PM
0 0 18 M
15
5 0 76 68
36 12 1
32
28 PM 100 200 300 400 500 600 700 800 900 1000
0F
24 30 Sheath Temperature—°C
20
ion
vect
16 l Con
rN atura
12 PM o
60 F
8
4

0
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
Sheath Temperature—°F

377
Air Heaters
Duct Heaters
LDH SERIES and D SERIES
Pressure Drop vs. Air Velocity Air Flow for ≥ 24kW
Air flow for
6 to 18kW
The rate at which pressure drops through the duct heater
is critical for properly sizing blowers and pumps. The
Pressure Drop vs. Air Velocity graph gives recommended
maximum velocities in feet per minute and meters per
Thermowell
minute according to the air velocity and duct heater size. 6kW
To determine the pressure drop through the duct heater, 9kW
12kW
follow the air velocity (FPM or MPM) over to the 18kW
appropriate curve, which identifies the duct heater >18kW
size. Then, take the intersecting point down to the Note: Viewing from the element ends—the
approximate pressure drop value. recommended air flow direction through
element bundle changes at >18kW.

WATROD Duct Heaters WATROD Duct Heaters

Pressure Drop vs. Air Velocity Pressure Drop vs. Air Velocity
2000 800
1900 750
1800 6
D
1700 D12 700
ter
t er ea
1600 ea 8
650 tH
ctH D1 uc
1500
Du ater D1 25 600
D
D D1
2
OD He 24 - O ter
1400 R ct rD 550 R ea
u ate H
D6

1300 W
AT DD uct He AT Du
ct
18
Air Velocity—MPM

O
Air Velocity—FPM

DD 500 W
ter

TR TRO OD er D
1200 WA WA TR eat
Hea

1100
450 WA uct
H
- D12
5
OD
D r D24
eate
uct

1000 400
AT
R ct H
W RO D Du
DD

900 350 WAT

TRO

800
300
700
WA

250
600
500 200
400 150
300 100
200
50
100

0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0.050

Approximate Pressure Drop—Inches of Water Approximate Pressure Drop—Kilopascals

Options
WATCONNECT® Standard Control Panels Features and Benefits
standard WATCONNECT® Lead times of two weeks or less
control panels are configured • Provides faster delivery than competition
to work with Watlow’s duct Full documentation provided for WATCONNECT
heaters. They are quickly control panels at the time of quotation
configured for process heating • Eliminates lengthy approval process and phone calls
applications and delivered within Incorporates Watlow’s temperature and power
two weeks. WATCONNECT controllers
panels integrate Watlow’s • Provides a turnkey solution for process heating
high-quality heater, sensor, applications
temperature controller and power controller products for
a complete thermal solution. Normally, competitive cus- Range of standard input/output (I/O) options
tom panels require significantly longer lead times. • Provides the user with a higher level of monitoring and
The broad range of standard features allow customers to control assuring an efficient and safe operation
quickly configure panels for each process heater included WATCONNECT enclosure easily mounts to wall or
in this catalog. frame
• Decreases installation time

378
Air Heaters
Duct Heaters
LDH SERIES and D SERIES Using a thermocouple requires an appropriate
temperature and power controller. These must be
Options (Continued) purchased separately. Watlow offers a wide variety of
Note: The WATCONNECT part number associated with temperature and power controllers to meet virtually all
a heater is only a suggestion. The following installation applications. Temperature controllers can be configured to
details need to be compared to panel capabilities to accept process variable inputs, too. Contact your Watlow
assure a compatible match: representative for details.
• Minimum and maximum ambient temperature where To order a thermocouple, add the appropriate suffix letter
panel will be installed to the duct heater’s base part number, as indicated on
• Statutory and regulatory requirements at installation the Ordering Information chart on page 390.
site
• Sun loading, if any, at installation site
• Presence of any hazardous gases, dusts or fibers, if any Thermowell
• Verification of process sensor type
• Verification of limit sensor type
• Input/Output (I/O) requirements
For additional product information see the Thermocouple
WATCONNECT landing page at www.watlow.com/
watconnect. On the WATCONNECT landing page you
will find a complete specification sheet along with other Duct heater thermowell holds thermocouple for sensing
sheath temperature.
tools to help you properly select your control panel. If
you would like to know the specific configuration of a Thermocouple Types
WATCONNECT part number, please use the Product Recommended 1
Configuration Lookup Tool on Watlow.com. ASTM Conductor Characteristics Temperature Range
Type Positive Negative °F (°C)
J Iron Constantan 0 to 1000 (-20 to 540)
Wattages/Voltages (Magnetic) (Non-magnetic)
To meet specific application needs, voltage and wattage K Chromel® Alumel® 0 to 2000 (-20 to 1100)
combinations outside stock product parameters (Non-magnetic) (Magnetic)
are available.
1Type J and Type K thermocouples are rated 32 to 1382°F and 32
For more information about this option, contact your to 2282°F (0-750°C and 0-1250°C), respectively. Watlow does not
Watlow representative. recommend exceeding temperature ranges shown on this chart for
the tubular product line.
Terminal Enclosures
Application Hints
In addition to the standard, general purpose terminal
enclosure, Watlow offers a moisture resistant optional • Mount duct heaters horizontally to lower enclosure
terminal enclosure to meet specific application temperatures and promote unit life.
requirements. • Orient heating elements as per the air flow illustration
on page 380.
Thermocouples • Promote heater life by keeping sheath temperature
Type J or K thermocouples, inserted in the thermowell, below the 1400°F (760°C) maximum.
accurately sense element sheath temperature for • Measure process temperature in the outlet stream,
over-temperature conditions. away from the heater.
• Maintain wiring integrity by keeping enclosure
To sense process temperature, the sensing element temperature below 400°F (205°C).
should be located downstream from the duct heater. This • Thermal cycling can cause terminations to loosen.
will eliminate incorrect sensing caused by radiant heat. Periodically check and tighten all electrical
Thermocouples are supplied with 120 in. (3050 mm) connections.
leads, longer lead lengths are available (this applies to “D” • Size power feeder wires in accordance with NEC and
SERIES only). Unless otherwise specified, thermocouples other applicable codes.
are supplied with temperature ranges detailed on the • Protect employees against electrical shock by properly
Thermocouple Types chart. grounding the unit per NEC specifications.

379
Air Heaters
Ext ended
Extended Capabilities for Duct Heaters Capabil it y
Performance Capabilities Options
• Wattages to 2.2 megawatts Sheath Material
Features and Benefits Watlow duct heaters can be made with the following
Ceramic fiber insulation available sheath materials:
• Keeps wiring cooler and reduces heat loss • 304, 316, 321 SS
Greater than 1/4 in. (6 mm) with 304 or 316 • Alloy 800
stainless steel flange material • Laminated alloy 600 (hi-temp)
• Easily bolts to the duct wall
• Hastelloy C276
60 plus element designs available
Contact your Watlow representative for details and
• Meets a wide variety of kilowatt demands
availability.
Terminal Enclosures
In addition to the standard, general purpose terminal
enclosure, Watlow offers the following optional terminal
enclosures to meet specific application
requirements:
• Explosion resistant (contact your Watlow
representative)
• High-temperature stand-off enclosures

380
Air Heaters
Duct Heaters ®
®
LDH SERIES
3½ in. G

Application: High Temperature Air

(89 mm) Typical
Typical

800°F (427°C) b D C

• Welded alloy 840 WATROD elements

• Without thermostat E
10½ in.
• General purpose enclosure (267 mm)

• Steel flange
1 3 and 6 element heaters have (1) 1 inch NPT conduit opening; 9 in.
(229 mm)
9, 12 and 15 element heaters have (2) 1 inch NPT conduit F
openings; 18 element heaters have (2) 11/2 inch NPT conduit 10½ in.
openings; 21 element (B= 201/4 in.) heaters have (2) 11/2 inch 1 (267 mm)
8¾ in.
NPT conduit openings; remaining 21 and 24 element heaters (222 mm)
have (3) 11/2 inch NPT conduit openings Ø 3⁄8 in. ¼ in.
(10 mm) 3½ in.
2 All flanges are 12 inches wide (6 mm)
(89 mm) B
8 in.
(203 mm) A

# of # Part WATCONNECT P/N Ship Wt. “A” Dim. “B” Dim. “C” Dim. “D” Dim. “E” Dim. “F” Dim. “G” Dim.
Elem Volts kW Ph Circ Number J T/C K T/C lbs (kg) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm)
20 W/in2 (3.1 W/cm2)
3 240 9.0 1 1 LDH9S10S C/F C/F 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
3 240 9.0 3 1 LDH9S3S C2-50 C2-92 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
3 480 9.0 1 1 LDH9S11S C/F C/F 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
3 480 9.0 3 1 LDH9S5S C2-43 C2-35 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
6 240 18.0 1 2 LDH18S10S C/F C/F 65 (30) 281/4 (718) 201/4 (514) 63/4 (171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
6 240 18.0 3 1 LDH18S3S C2-236 C2-214 65 (30) 281/4 (718) 201/4 (514) 63/4 (171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
6 480 18.0 1 1 LDH18S11S C/F C/F 65 (30) 281/4 (718) 201/4 (514) 63/4 (171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
6 480 18.0 3 1 LDH18S5S C2-43 C2-35 65 (30) 281/4 (718) 201/4 (514) 63/4 (171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
9 240 27.0 1 3 LDH27S10S C/F C/F 120 (55) 281/4 (718) 201/4 (514) 93/4 (248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
9 240 27.0 3 3 LDH27S3S C4-143 C4-142 120 (55) 281/4 (718) 201/4 (514) 93/4 (248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
9 480 27.0 1 3 LDH27S11S C/F C/F 120 (55) 281/4 (718) 201/4 (514) 93/4 (248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
9 480 27.0 3 1 LDH27S5S C2-225 C2-226 120 (55) 281/4 (718) 201/4 (514) 93/4 (248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
12 240 36.0 1 4 LDH36S10S C/F C/F 135 (62) 281/4 (718) 201/4 (514) 123/4 (324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
12 240 36.0 3 2 LDH36S3S C2-218 C2-224 135 (62) 281/4 (718) 201/4 (514) 123/4 (324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
12 480 36.0 1 2 LDH36S11S C/F C/F 135 (62) 281/4 (718) 201/4 (514) 123/4 (324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
12 480 36.0 3 1 LDH36S5S C2-225 C2-226 135 (62) 281/4 (718) 201/4 (514) 123/4 (324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
15 240 45.0 3 5 LDH45S3S C4-144 C4-145 195 (89) 281/4 (718) 201/4 (514) 153/4 (400) 191/2 (495) 16 (406) 177/8 (454.0) 3 (76)
15 480 45.0 1 3 LDH45S11S C/F C/F 195 (89) 281/4 (718) 201/4 (514) 153/4 (400) 191/2 (495) 16 (406) 177/8 (454.0) 3 (76)
15 480 45.0 3 5 LDH45S5S C4-150 C4-151 195 (89) 281/4 (718) 201/4 (514) 153/4 (400) 191/2 (495) 16 (406) 177/8 (454.0) 3 (76)
18 240 54.0 3 3 LDH54S3S C4-144 C4-145 205 (93) 281/4 (718) 201/4 (514) 183/4 (476) 221/2 (572) 19 (483) 207/8 (530.2) 3 (76)
18 480 54.0 1 3 LDH54S11S C/F C/F 205 (93) 281/4 (718) 201/4 (514) 183/4 (476) 221/2 (572) 19 (483) 207/8 (530.2) 3 (76)
18 480 54.0 3 2 LDH54S5S C2-229 C2-230 205 (93) 281/4 (718) 201/4 (514) 183/4 (476) 221/2 (572) 19 (483) 207/8 (530.2) 3 (76)
21 240 63.0 3 7 LDH63S3S C4-148 C4-149 235 (107) 281/4 (718) 201/4 (514) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 63.0 1 3 LDH63S11S C/F C/F 235 (107) 281/4 (718) 201/4 (514) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 63.0 3 7 LDH63S5S C4-154 C4-155 235 (107) 281/4 (718) 201/4 (514) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 240 79.0 3 7 LDH79S3S C/F C/F 260 (118) 33 (838) 25 (635) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 79.0 1 7 LDH79S11S C/F C/F 260 (118) 33 (838) 25 (635) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 79.0 3 7 LDH79S5S C4-156 C4-157 260 (118) 33 (838) 25 (635) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 240 105.0 3 7 LDH105S3S C/F C/F 290 (132) 401/2 (1029) 321/2 (826) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 105.0 1 7 LDH105S11S C/F C/F 290 (132) 401/2 (1029) 321/2 (826) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 105.0 3 7 LDH105S5S C4-156 C4-157 290 (132) 401/2 (1029) 321/2 (826) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 131.0 3 7 LDH131S5S C4-156 C4-157 310 (141) 491/2 (1257) 411/2 (1054) 213/4 (552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
24 480 150.0 3 4 LDH150S5S C4-156 C4-157 330 (150) 491/2 (1257) 411/2 (1054) 243/4 (629) 281/2 (724) 25 (635) 267/8 (682.6) 3 (76)
Notes:
• See Watt Density vs. Air Temperature/Velocity charts on C/F - Contact factory, go to www.watlow.com/en/contact-us
page 379 to confirm suitability in the application.

381
Air Heaters
Duct Heaters ®
®
LDH SERIES
Application: Medium Temperature Air 3½ in. G
750°F (399°C) (89 mm)
Typical
Typical

b D C
• Welded alloy 840 WATROD elements
• Without thermostat
• General purpose enclosure
E
• Steel flange 10½ in.
(267 mm)

1 3 and 6 element heaters have (1) 1 inch NPT conduit opening;

9, 12 and 15 element heaters have (2) 1 inch NPT conduit 9 in.
openings; 18 element heaters have (2) 11/2 inch NPT conduit (229 mm)
F
openings; 21 element (B= 201/4 in.) heaters have (2) 11/2 inch
10½ in.
NPT conduit openings; remaining 21 and 24 element heaters 1 (267 mm)
have (3) 11/2 inch NPT conduit openings 8¾ in.
(222 mm)
2 All flanges are 12 inches wide Ø 3⁄8 in. ¼ in.
(10 mm)
(6 mm) 3½ in.
(89 mm) B
8 in.
(203 mm) A

# of # Part WATCONNECT P/N Ship Wt. “A” Dim. “B” Dim. “C” Dim. “D” Dim. “E” Dim. “F” Dim. “G” Dim.
Elem Volts kW Ph Circ Number J T/C K T/C lbs. (kg) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm)
30 W/in2 (4.7 W/cm2)
3 240 14.0 1 3 LDH14SX10S C/F C/F 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
3 240 14.0 3 1 LDH14SX3S C2-236 C2-214 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
3 480 14.0 1 1 LDH14SX11S C/F C/F 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
3 480 14.0 3 1 LDH14SX5S C2-43 C2-35 55 (25) 281/4 (718) 201/4 (514) 33/4 (95) 71/2 (191) 4 (102) 45/8 (117.5) 3 (76)
6 240 27.0 1 3 LDH27SX10S C/F C/F 65 (30) 281/4 (718) 201/4 (514) 63/4(171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
6 240 27.0 3 2 LDH27SX3X C2-218 C2-224 65 (30) 281/4 (718) 201/4 (514) 63/4(171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
6 480 27.0 1 2 LDH27SX11S C/F C/F 65 (30) 281/4 (718) 201/4 (514) 63/4(171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
6 480 27.0 3 1 LDH27SX5S C2-225 C2-226 65 (30) 281/4 (718) 201/4 (514) 63/4(171) 101/2 (267) 7 (178) 75/8 (193.7) 3 (76)
9 240 41.0 3 3 LDH41SX3S C4-144 C4-145 120 (55) 281/4 (718) 201/4 (514) 93/4(248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
9 480 41.0 1 3 LDH41SX11S C/F C/F 120 (55) 281/4 (718) 201/4 (514) 93/4(248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
9 480 41.0 3 3 LDH41SX5S C4-150 C4-151 120 (55) 281/4 (718) 201/4 (514) 93/4(248) 131/2 (343) 10 (254) 105/8 (269.9) 3 (76)
12 240 54.0 3 4 LDH54SX3S C4-148 C4-149 135 (62) 281/4 (718) 201/4 (514) 123/4(324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
12 480 54.0 1 3 LDH54SX11S C/F C/F 135 (62) 281/4 (718) 201/4 (514) 123/4(324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
12 480 54.0 3 2 LDH54SX5S C2-229 C2-230 135 (62) 281/4 (718) 201/4 (514) 123/4(324) 161/2 (419) 13 (330) 135/8 (346.1) 3 (76)
15 240 68.0 3 5 LDH68SX3S C/F C/F 195 (89) 281/4 (718) 201/4 (514) 153/4(400) 191/2 (495) 16 (406) 177/8 (454.0) 3 (76)
15 480 68.0 1 3 LDH68SX11S C/F C/F 195 (89) 281/4 (718) 201/4 (514) 153/4(400) 191/2 (495) 16 (406) 177/8 (454.0) 3 (76)
15 480 68.0 3 5 LDH68SX5S C4-152 C4-153 195 (89) 281/4 (718) 201/4 (514) 153/4(400) 191/2 (495) 16 (406) 177/8 (454.0) 3 (76)
18 240 80.0 3 6 LDH80SX3S C/F C/F 205 (93) 281/4 (718) 201/4 (514) 183/4(476) 221/2 (572) 19 (483) 207/8 (530.2) 3 (76)
18 480 80.0 1 6 LDH80SX11S C/F C/F 205 (93) 281/4 (718) 201/4 (514) 183/4(476) 221/2 (572) 19 (483) 207/8 (530.2) 3 (76)
18 480 80.0 3 3 LDH80SX5S C4-152 C4-153 205 (93) 281/4 (718) 201/4 (514) 183⁄4(476) 221/2 (572) 19 (483) 207/8 (530.2) 3 (76)
21 240 95.0 3 7 LDH95SX3S C/F C/F 235 (107) 281/4 (718) 201/4 (514) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 95.0 1 7 LDH95SX11S C/F C/F 235 (107) 281/4 (718) 201/4 (514) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 95.0 3 7 LDH95SX5S C4-156 C4-157 235 (107) 281/4 (718) 201/4 (514) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 240 120.0 3 7 LDH120SX3S C/F C/F 260 (118) 33 (838) 25 (635) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 120.0 1 7 LDH120SX11S C/F C/F 260 (118) 33 (838) 25 (635) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 120.0 3 7 LDH120SX5S C4-156 C4-157 260 (118) 33 (838) 25 (635) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
21 480 160.0 3 7 LDH160SX5S C/F C/F 290 (132) 401/2(1029) 32 /2 (826) 213/4(552) 251/2 (648)
1 22 (559) 237/8 (606.4) 3 (76)
21 480 200.0 3 7 LDH200SX5S C/F C/F 310 (141) 491/2(1257) 411/2 (1054) 213/4(552) 251/2 (648) 22 (559) 237/8 (606.4) 3 (76)
24 480 225.0 3 8 LDH225SX5S C/F C/F 330 (150) 491/2(1257) 411/2 (1054) 243/4(629) 281/2 (724) 25 (635) 267/8 (682.6) 3 (76)
Notes:
• See Watt Density vs. Air Temperature/Velocity charts on C/F - Contact factory, go to www.watlow.com/en/contact-us
page 379 to confirm suitability in the application.

382
Air Heaters
Duct Heaters ®
®
D SERIES
Application: High Temperature Air a
D
C
G
Typical
b 3½ in.
800°F (427°C) (89 mm)
Typical
• Removable alloy 840 WATROD elements
• Without thermostat 115⁄8 in. E
• General purpose enclosure (295 mm)
9 in.
• Steel flange (229 mm)

10½ in.
1 6 and 12 element heaters have (1) 1 inch NPT conduit (267 mm)

opening; 18, 24, 30 and 42 element heaters have

8¾ in.
(2) 1 inch NPT conduit openings; 36, 48, 54 and 60 F
(222 mm)
3½ in. B
element heaters have (2) 1 inch NPT and (2) 11/4 inch 3⁄8 in. (89 mm)
A
conduit openings (10 mm)
Diameter 77⁄8 in. (200 mm)
2 All flanges are 12 inches wide ¼ in.
(6 mm)

# of # Part WATCONNECT P/N Ship Wt. “A” Dim. “B” Dim. “C” Dim. “D” Dim. “E” Dim. “F” Dim. “G” Dim.
Elem. Volts kW Ph Circ Number J T/C K T/C lbs. (kg) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm)
20 W/in2 (3.1 W/cm2)
6 240 6.0 1 1 D6S10S C/F C/F 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
6 240 6.0 3 1 D6S3S C2-50 C2-92 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
6 480 6.0 1 1 D6S11S C/F C/F 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
6 480 6.0 3 1 D6S5S C2-43 C2-35 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
12 240 12.0 1 1 D12S10S C/F C/F 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
12 240 12.0 3 1 D12S3S C2-236 C2-214 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
12 480 12.0 1 1 D12S11S C/F C/F 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
12 480 12.0 3 1 D12S5S C2-43 C2-35 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
18 240 18.0 1 2 D18S10S C/F C/F 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
18 240 18.0 3 1 D18S3S C2-236 C2-214 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
18 480 18.0 1 1 D18S11S C/F C/F 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
18 480 18.0 3 1 D18S5S C2-43 C2-35 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
24 240 24.0 1 2 D24S10S C/F C/F 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
24 240 24.0 3 2 D24S3S C2-218 C2-224 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
24 480 24.0 1 1 D24S11S C/F C/F 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
24 480 24.0 3 1 D24S5S C2-225 C2-226 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
30 240 30.0 3 2 D30S3S C2-218 C2-224 120 (55) 277/8 (708) 20 (508) 103/4 (273) 141/2 (368) 11 (279) 133/4 (349) 31/4 (83)
30 480 30.0 1 2 D30S11S C/F C/F 120 (55) 277/8 (708) 20 (508) 103/4 (273) 141/2 (368) 11 (279) 133/4 (349) 31/4 (83)
30 480 30.0 3 1 D30S5S C2-225 C2-226 120 (55) 277/8 (708) 20 (508) 103/4 (273) 141/2 (368) 11 (279) 133/4 (349) 31/4 (83)
CONTINUED
Notes:
• See Watt Density vs. Air Temperature/Velocity charts on page 379 to C/F - Contact factory, go to www.watlow.com/en/contact-us
confirm suitability in the application.

383
Air Heaters
Duct Heaters ®
®
D SERIES
Application: High Temperature Air D G
a C Typical
800°F (427°C) b 3½ in.
(89 mm)
Typical
• Removable alloy 840 WATROD elements
• Without thermostat
115⁄8 in. E
• General purpose enclosure (295 mm)
9 in.
• Steel flange (229 mm)

10½ in.
1 6 and 12 element heaters have (1) 1 inch NPT conduit (267 mm)

opening; 18, 24, 30 and 42 element heaters have 8¾ in.

F
(2) 1 inch NPT conduit openings; 36, 48, 54, and 60 3½ in.
(222 mm)
B
element heaters have (2) 1 inch NPT and (2) 11/4 inch 3⁄8 in. (89 mm)
A
(10 mm)
conduit openings Diameter 77⁄8 in. (200 mm)
¼ in.
2 All flanges are 12 inches wide (6 mm)

# of # Part WATCONNECT P/N Ship Wt. “A” Dim. “B” Dim. “C” Dim. “D” Dim. “E” Dim. “F” Dim. “G” Dim.
Elem. Volts kW Ph Circ Number J T/C K T/C lbs. (kg) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm)
20 W/in2 (3.1 W/cm2)
36 240 36.0 3 2 D36S3S C2-218 C2-219 135 (62) 277/8 (708.0) 20 (508) 123/4 (324) 161/2 (419) 13 (330) 153/4 (400) 33/4 (95)
36 480 36.0 1 2 D36S11S C/F C/F 135 (62) 277/8 (708.0) 20 (508) 123/4 (324) 161/2 (419) 13 (330) 153/4 (400) 33/4 (95)
36 480 36.0 3 1 D36S5S C2-225 C2-226 135 (62) 277/8 (708.0) 20 (508) 123/4 (324) 161/2 (419) 13 (330) 153/4 (400) 33/4 (95)
42 240 42.0 3 2 D42S3S C/F C/F 155 (71) 277/8 (708.0) 20 (508) 143/4 (375) 181/2 (470) 15 (381) 173/4 (451) 41/4 (108)
42 480 42.0 1 2 D42S11S C/F C/F 155 (71) 277/8 (708.0) 20 (508) 143/4 (375) 181/2 (470) 15 (381) 173/4 (451) 41/4 (108)
42 480 42.0 3 2 D42S5S C2-229 C2-230 155 (71) 277/8 (708.0) 20 (508) 143/4 (375) 181/2 (470) 15 (381) 173/4 (451) 41/4 (108)
48 240 48.0 3 4 D48S3S C4-148 C4-149 195 (89) 277/8 (708.0) 20 (508) 163/4 (425) 201/2 (521) 17 (432) 193/4 (502) 43/4 (121)
48 480 48.0 1 2 D48S11S C/F C/F 195 (89) 277/8 (708.0) 20 (508) 163/4 (425) 201/2 (521) 17 (432) 193/4 (502) 43/4 (121)
48 480 48.0 3 2 D48S5S C2-229 C2-230 195 (89) 277/8 (708.0) 20 (508) 163/4 (425) 201/2 (521) 17 (432) 193/4 (502) 43/4 (121)
54 240 54.0 3 3 D54S3S C4-144 C4-145 205 (93) 277/8 (708.0) 20 (508) 183/4 (476) 221/2 (572) 19 (483) 213/4 (552) 51/4 (133)
54 480 54.0 1 3 D54S11S C/F C/F 205 (93) 277/8 (708.0) 20 (508) 183/4 (476) 221/2 (572) 19 (483) 213/4 (552) 51/4 (133)
54 480 54.0 3 2 D54S5S C2-229 C2-230 205 (93) 277/8 (708.0) 20 (508) 183/4 (476) 221/2 (572) 19 (483) 213/4 (552) 51/4 (133)
60 240 60.0 3 4 D60S3S C4-148 C4-149 235 (107) 277/8 (708.0) 20 (508) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 60.0 1 4 D60S11S C/F C/F 235 (107) 277/8 (708.0) 20 (508) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 60.0 3 2 D60S5S C2-229 C2-230 235 (107) 277/8 (708.0) 20 (508) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 240 75.0 3 4 D75S3S C4-148 C4-149 260 (118) 327/8 (835.0) 25 (635) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 75.0 1 4 D75S11S C/F C/F 260 (118) 327/8 (835.0) 25 (635) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 75.0 3 2 D75S5S C2-229 C2-230 260 (118) 327/8 (835.0) 25 (635) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 100.0 3 4 D100S5S C4-156 C4-157 290 (132) 403/8 (1025.5) 321/2 (826) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 125.0 3 4 D125S5S C4-156 C4-157 310 (141) 493/8 (1254.1) 411/2 (1054) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
Notes:
• See Watt Density vs. Air Temperature/Velocity charts on page 379 to C/F - Contact factory, go to www.watlow.com/en/contact-us
confirm suitability in the application.

384
Air Heaters
Duct Heaters ®
®
D SERIES
Application: Medium Temperature Air
750°F (399°C) a
D
C
G
Typical
b 3½ in.
• Removable alloy 840 WATROD elements (89 mm)
Typical
• Without thermostat
• General purpose enclosure
• Steel flange 115⁄8 in.
(295 mm)
E

9 in.
(229 mm)
1 6 and 12 element heaters have (1) 1 inch NPT conduit
10½ in.
opening; 18, 24, 30 and 42 element heaters have (267 mm)
(2) 1 inch NPT conduit openings; 36, 48, 54, and 60
element heaters have (2) 1 inch NPT and (2) 11/4 inch F
8¾ in.
(222 mm)
conduit openings 3½ in. B
(89 mm)
3⁄8 in.
2 All flanges are 12 inches wide (10 mm)
A
Diameter 77⁄8 in. (200 mm)
¼ in.
(6 mm)

# of # Part WATCONNECT P/N Ship Wt. “A” Dim. “B” Dim. “C” Dim. “D” Dim. “E” Dim. “F” Dim. “G” Dim.
Elem. Volts kW Ph Circ Number J T/C K T/C lbs. (kg) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm)
30 W/in2 (4.7 W/cm2)
6 240 9.0 1 1 D6SX10S C/F C/F 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
6 240 9.0 3 1 D6SX3S C2-50 C2-92 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
6 480 9.0 1 1 D6SX11S C/F C/F 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
6 480 9.0 3 1 D6SX5S C2-43 C2-35 50 (23) 277/8 (708) 20 (508) 23/4 (70) 61/2 (165) 3 (76) 53/4 (146) 21/2 (64)
12 240 18.0 1 2 D12SX10S C/F C/F 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
12 240 18.0 3 1 D12SX3S C2-236 C2-214 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
12 480 18.0 1 1 D12SX11S C/F C/F 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
12 480 18.0 3 1 D12SX5S C2-43 C2-35 55 (25) 277/8 (708) 20 (508) 43/4 (121) 81/2 (215) 5 (127) 73/4 (197) 31/2 (89)
18 240 27.0 1 3 D18SX10S C/F C/F 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
18 240 27.0 3 2 D18SX3S C2-218 C2-224 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
18 480 27.0 1 2 D18SX11S C/F C/F 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
18 480 27.0 3 1 D18SX5S C2-225 C2-226 65 (30) 277/8 (708) 20 (508) 63/4 (171) 101/2 (267) 7 (178) 93/4 (248) 3 (76)
24 240 36.0 1 4 D24SX10S C/F C/F 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
24 240 36.0 3 2 D24SX3S C2-218 C2-219 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
24 480 36.0 1 2 D24SX11S C/F C/F 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
24 480 36.0 3 1 D24SX5S C2-225 C2-226 95 (43) 277/8 (708) 20 (508) 83/4 (222) 121/2 (318) 9 (229) 113/4 (298) 23/4 (70)
30 240 45.0 3 5 D30SX3S C4-144 C4-145 120 (55) 277/8 (708) 20 (508) 103/4 (273) 141/2 (368) 11 (279) 133/4 (349) 31/4 (83)
30 480 45.0 1 2 D30SX11S C/F C/F 120 (55) 277/8 (708) 20 (508) 103/4 (273) 141/2 (368) 11 (279) 133/4 (349) 31/4 (83)
30 480 45.0 3 2 D30SX5S C2-229 C2-230 120 (55) 277/8 (708) 20 (508) 103/4 (273) 141/2 (368) 11 (279) 133/4 (349) 31/4 (83)
CONTINUED
Notes:
• See Watt Density vs. Air Temperature/Velocity charts on page 379 to C/F - Contact factory, go to www.watlow.com/en/contact-us
confirm suitability in the application.

385
Air Heaters
Duct Heaters ®
®
D SERIES
D G
a C Typical
b 3½ in.
Application: Medium Temperature Air (89 mm)
Typical
750°F (399°C)
• Removable alloy 840 WATROD elements
115⁄8 in. E
• Without thermostat (295 mm)
9 in.
• General purpose enclosure (229 mm)

• Steel flange 10½ in.

(267 mm)

1 6 and 12 element heaters have (1) 1 inch NPT conduit 8¾ in.

F
opening; 18, 24, 30 and 42 element heaters have 3½ in.
(222 mm)
B
(2) 1 inch NPT conduit openings; 36, 48, 54, and 60 3⁄8 in. (89 mm)
A
element heaters have (2) 1 inch NPT and (2) 11/4 inch (10 mm)
Diameter 77⁄8 in. (200 mm)
conduit openings ¼ in.
(6 mm)
2 All flanges are 12 inches wide

# of # Part WATCONNECT P/N Ship Wt. “A” Dim. “B” Dim. “C” Dim. “D” Dim. “E” Dim. “F” Dim. “G” Dim.
Elem. Volts kW Ph Circ Number J T/C K T/C lbs. (kg) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm) in. (mm)
30 W/in2 (4.7 W/cm2)
36 240 54.0 3 3 D36SX3S C4-144 C4-145 135 (62) 277/8 (708.0) 20 (508) 123/4 (324) 161/2 (419) 13 (330) 153/4 (400) 33/4 (95)
36 480 54.0 1 3 D36SX11S C/F C/F 135 (62) 277/8 (708.0) 20 (508) 123/4 (324) 161/2 (419) 13 (330) 153/4 (400) 33/4 (95)
36 480 54.0 3 2 D36SX5S C2-229 C2-230 135 (62) 277/8 (708.0) 20 (508) 123/4 (324) 161/2 (419) 13 (330) 153/4 (400) 33/4 (95)
42 240 63.0 3 7 D42SX3S C4-148 C4-149 155 (71) 277/8 (708.0) 20 (508) 143/4 (375) 181/2 (470) 15 (381) 173/4 (451) 41/4 (108)
42 480 63.0 1 3 D42SX11S C/F C/F 155 (71) 277/8 (708.0) 20 (508) 143/4 (375) 181/2 (470) 15 (381) 173/4 (451) 41/4 (108)
42 480 63.0 3 2 D42SX5S C2-229 C2-230 155 (71) 277/8 (708.0) 20 (508) 143/4 (375) 181/2 (470) 15 (381) 173/4 (451) 41/4 (108)
48 240 72.0 3 4 D48SX3S C4-148 C4-149 195 (89) 277/8 (708.0) 20 (508) 163/4 (425) 201/2 (521) 17 (432) 193/4 (502) 43/4 (121)
48 480 72.0 1 4 D48SX11S C/F C/F 195 (89) 277/8 (708.0) 20 (508) 163/4 (425) 201/2 (521) 17 (432) 193/4 (502) 43/4 (121)
48 480 72.0 3 2 D48SX5S C2-229 C2-230 195 (89) 277/8 (708.0) 20 (508) 163/4 (425) 201/2 (521) 17 (432) 193/4 (502) 43/4 (121)
54 240 81.0 3 6 D54SX3S C/F C/F 205 (93) 277/8 (708.0) 20 (508) 183/4 (476) 221/2 (572) 19 (483) 213/4 (552) 51/4 (133)
54 480 81.0 1 6 D54SX11S C/F C/F 205 (93) 277/8 (708.0) 20 (508) 183/4 (476) 221/2 (572) 19 (483) 213/4 (552) 51/4 (133)
54 480 81.0 3 3 D54SX5S C4-152 C4-153 205 (93) 277/8 (708.0) 20 (508) 183/4 (476) 221/2 (572) 19 (483) 213/4 (552) 51/4 (133)
60 240 90.0 3 5 D60SX3S C/F C/F 235 (107) 277/8 (708.0) 20 (508) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 90.0 1 4 D60SX11S C/F C/F 235 (107) 277/8 (708.0) 20 (508) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 90.0 3 4 D60SX5S C4-156 C4-157 235 (107) 277/8 (708.0) 20 (508) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 240 115.0 3 10 D75SX3S C/F C/F 260 (118) 327/8 (835.0) 25 (635) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 115.0 1 5 D75SX11S C/F C/F 260 (118) 327/8 (835.0) 25 (635) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 115.0 3 4 D75SX5S C4-156 C4-157 260 (118) 327/8 (835.0) 25 (635) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 150.0 3 4 D100SX5S C4-156 C4-157 290 (132) 403/8 (1025.5) 321/2 (826) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
60 480 190.0 3 5 D125SX5S C/F C/F 310 (141) 493/8 (1254.1) 411/2 (1054) 203/4 (527) 241/2 (622) 21 (533) 233/4 (603) 53/4 (146)
Notes:
• See Watt Density vs. Air Temperature/Velocity charts on page 379 to C/F - Contact factory, go to www.watlow.com/en/contact-us
confirm suitability in the application.

386
Air Heaters
Duct Heaters
D SERIES
Replacement Elements
Replaceable heating elements provide easy field service To order replacement elements, specify the replacement
and reduce downtime. Element change-out is made element part number (from the table) that corresponds
simple by a single screw clamp. to the original Watlow duct heater part number. Then,
specify quantity.

Replacement Elements
Original Replacement Original Duct Replacement
Duct Heater Element Heater “A” Dim. Element Est. Net Wt.
Part Numbers Volts Watts in. (mm) Part Number lbs (kg)
20 W/in2 (3.1 W/cm2)
D6S3 to D60S3 240 1000 277/8 (708.0) D6240 1.0 (0.5)
D6S5 to D60S5 480 1000 277/8 (708.0) D6480 1.0 (0.5)
D75S3 240 1250 327/8 (835.0) D75240 1.0 (0.5)
D75S5 480 1250 327/8 (835.0) D75480 1.0 (0.5)
D100S5 480 1667 403/8 (1025.5) D100480 1.4 (0.7)
D125S5 480 2083 493/8 (1254.1) D125480 1.7 (0.8)
30 W/in2 (4.7 W/cm2)
D6SX3 to D60SX3 240 1500 277/8 (708.0) D6X240 1.0 (0.5)
D6SX5 to D60SX5 480 1500 277/8 (708.0) D6X480 1.0 (0.5)
D75SX3 240 1917 327/8 (835.0) D75X240 1.0 (0.5)
D75SX5 480 1917 327/8 (835.0) D75X480 1.0 (0.5)
D100SX5 480 2500 403/8 (1025.5) D100X480 1.4 (0.7)
D125SX5 480 3167 493/8 (1254.1) D125X480 1.7 (0.8)

387
Air Heaters
Duct Heaters
LDH SERIES and D SERIES
Part Number
Optional Optional Sheath
Stock Duct Terminal Process Limit
Part Number Enclosures Sensors Sensors

Stock Duct Part Number

Note: Catalog part numbers include optional enclosures. To order
optional enclosures or sensors, substitute the appropriate suffix.

Optional Terminal Enclosures

S= General purpose enclosure
W= Moisture resistant enclosure
Note: Catalog listing is a general purpose enclosure. Substitute
enclosure options are noted.

Optional Bulb & Capillary Thermostats or

Thermocouple Process Sensors
PJ = Type J process thermocouple in thermowell
PK= Type K process thermocouple in thermowell

Sheath Limit Sensors

HJ= Type J high-limit thermocouple
HK= Type K high-limit thermocouple

Example Part Number: D6SX10 S J HJ

388
Air Heaters
Duct Heaters
MDH SERIES
Watlow’s line of process air heaters offer improved
performance and increased versatility in medium to low
temperature applications.
The duct heaters are modular and consist of two parts.
The first is a six kilowatt heater available in either 240 or
480 volts, single- or three-phase.
The second part of the heater consists of the electrical
terminal enclosure protecting each module’s termination
area and a main flange that bolts into the user’s
ductwork. The heater modules are installed in the
housing and main flange via rectangular slots in the
main flange. The range of modules that can be
accommodated in various duct heater assemblies
range from one to 10 modules. A range of six to
60 kilowatts, in six kilowatt increments is achieved.
The new design of the modular duct heater offers
increased reliability. The individual modules are removable
through the terminal enclosure of the assembly, which Typical Applications
eliminates the need to pull the complete heater from the • Low temperature ovens
ductwork. This reduces downtime and costs because
• Parts drying
the heating elements can be replaced individually.
• Semiconductor cleanroom environmental heating
Performance improvements include quicker response
• Plastic curing
time and reduced infiltration from the air stream being
heated into the electrical enclosure. • Load banks
• Heated air knives
Features and Benefits
• Food dehydration
Individual modules removable through housing
• Reduces downtime for replacement of module • Heat shrink tunnels
Smaller diameter elements (0.315 inch)
• Results in a 25 percent lower energy usage on
initial heat-up
27 percent reduction in heat-up time as compared
to traditional 0.430 inch diameter duct heater
elements
• Results in faster response time
31 percent lighter weight than traditional tubular
duct heaters
• Reduces shipping costs and increases worker safety
Greater free cross sectional area
• Results in lower pressure drop
Improved seal between element and electrical
terminal enclosure
• Results in lower electrical terminal enclosure
temperature
Flexible module wiring
• Allows user to sequentially stage modules

389
Air Heaters
Duct Heaters
MDH SERIES
Velocity vs. Process Temperature
Modular Duct Heater – Velocity vs. Process Temperature

40 W/in2 30 W/in2 26 W/in2 23 W/in2 18 W/in2

1600
1500
1400
1300
1200

1100
Velocity – Feet/Min

1000 8 W/in2
900
800
700
600
500
400

300
200
100
0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Process Temperature (°F)

Based on 70°F Inlet
Air Temperature

Watt Density vs. Sheath Temperature

Modular Duct Heater – Watt Density vs. Sheath Temperature

1550 FPM 1200 FPM 760 FPM 600 FPM

50

40
Watt Density-W/in2

300 FPM
30

60 FPM
20 Natural
Convection

10

0
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Sheath Temperature (°F)

390
Air Heaters
Duct Heaters ®
®
MDH SERIES D
Typ.
A

31/2 in. (89 mm)

Typ.

B 115/8 in.
(295 mm)
8 in.
m)
(203 m
101 /2 in.
(267 mm)

C
213/4 in. 12 in. 1/4 in.

(552 mm) (305 mm) (6.35 mm)

261/16 in. 3/8 in.
(662 mm)
(9.5 mm)
Diameter

Application: Air Heating – Maximum Outlet Temperature – 750°F (399°C)

WATCONNECT Dimensions
P/N in.
Watt Est.
Density No. of No. of Shipping Wt. Part
W/in 2 kW Volts Phase Circuits Modules lbs Number J T/C K T/C A B C D
26 6 240 1 1 1 35 MDH6S10 C/F C/F 6.50 2.50 5.75 2.50
26 6 240 3 1 1 35 MDH6S3 C2-50 C2-92 6.50 2.50 5.75 2.50
26 6 480 1 1 1 35 MDH6S11 C/F C/F 6.50 2.50 5.75 2.50
26 6 480 3 1 1 35 MDH6S5 C2-43 C2-35 6.50 2.50 5.75 2.50
26 12 240 1 2 2 39 MDH12S10 C/F C/F 8.50 4.75 7.75 3.50
26 12 240 3 1 2 39 MDH12S3 C2-236 C2-214 8.50 4.75 7.75 3.50
26 12 480 1 1 2 39 MDH12S11 C/F C/F 8.50 4.75 7.75 3.50
26 12 480 3 1 2 39 MDH12S5 C2-43 C2-35 8.50 4.75 7.75 3.50
26 18 240 1 3 3 46 MDH18S10 C/F C/F 10.50 7.00 9.75 3.00
26 18 240 3 1 3 46 MDH18S3 C2-236 C2-214 10.50 7.00 9.75 3.00
26 18 480 1 1 3 46 MDH18S11 C/F C/F 10.50 7.00 9.75 3.00
26 18 480 3 1 3 46 MDH18S5 C2-43 C2-35 10.50 7.00 9.75 3.00
26 24 240 1 4 4 67 MDH24S10 C/F C/F 12.50 9.25 11.75 2.75
26 24 240 3 2 4 67 MDH24S3 C2-218 C2-224 12.50 9.25 11.75 2.75
26 24 480 1 2 4 67 MDH24S11 C/F C/F 12.50 9.25 11.75 2.75
26 24 480 3 1 4 67 MDH24S5 C2-225 C2-226 12.50 9.25 11.75 2.75
26 30 240 3 2 5 84 MDH30S3 C2-218 C2-224 15.75 11.50 15.00 3.56
26 30 480 1 2 5 84 MDH30S11 C/F C/F 15.75 11.50 15.00 3.56
26 30 480 3 1 5 84 MDH30S5 C2-225 C2-226 15.75 11.50 15.00 3.56
26 36 240 3 2 6 95 MDH36S3 C2-218 C2-224 18.00 13.75 17.25 4.13
26 36 480 1 2 6 95 MDH36S11 C/F C/F 18.00 13.75 17.25 4.13
26 36 480 3 1 6 95 MDH36S5 C2-225 C2-226 18.00 13.75 17.25 4.13
26 42 240 3 3 7 109 MDH42S3 C4-144 C4-145 20.25 16.00 19.50 4.69
26 42 480 1 3 7 109 MDH42S11 C/F C/F 20.25 16.00 19.50 4.69
26 42 480 3 2 7 109 MDH42S5 C2-229 C2-230 20.25 16.00 19.50 4.69
26 48 240 3 4 8 137 MDH48S3 C4-148 C4-149 22.50 18.25 21.75 5.25
26 48 480 1 3 8 137 MDH48S11 C/F C/F 22.50 18.25 21.75 5.25
26 48 480 3 2 8 137 MDH48S5 C2-229 C2-230 22.50 18.25 21.75 5.25
26 54 240 3 3 9 144 MDH54S3 C4-144 C4-145 24.75 20.50 24.00 5.81
26 54 480 1 3 9 144 MDH54S11 C/F C/F 24.75 20.50 24.00 5.81
26 54 480 3 2 9 144 MDH54S5 C2-229 C2-230 24.75 20.50 24.00 5.81
26 60 240 3 4 10 165 MDH60S3 C4-148 C4-149 27.00 22.75 26.25 6.38
26 60 480 1 4 10 165 MDH60S11 C/F C/F 27.00 22.75 26.25 6.38
26 60 480 3 2 10 165 MDH60S5 C2-229 C2-230 27.00 22.75 26.25 6.38
Options include individual modules with optional general purpose terminal enclosure, high-temperature thermocouple kit and blank flange modules.
C/F - Contact factory, go to www.watlow.com/en/contact-us
Modular duct heaters with 1 and 2 modules have conduit openings for one, 1 inch NPT fitting.
Modular duct heaters with 3, 4, 5, and 7 modules have conduit openings for two, 1 inch NPT fittings.
Modular duct heaters with 6, 8, 9, and 10 modules have conduit openings for two, 11/4 inch NPT and two, 1 inch NPT fittings.
391
Air Heaters
Duct Heaters
MDH SERIES
Individual Module Dimensions
Specifications 2¼ in.
(57 mm)
• Module rating - 240 or 480VAC, 6kW, three-phase
or one-phase TOP

• Watt density - 26 W/in2 8¼ in.

(210 mm)
• Elements - 0.315 inch dia. alloy 840 elements
+
• High-limit thermocouple installed by drilling

Watlow Modular Duct Heater

7½ in.

6000 W. 480 V, 3PH, XXXX

(191

PN XXXXXXXXX
premarked hole in flange mm)

• 6-60kW range when mounted in duct heater

assembly 22 in.
(559 mm)

Application Information
• Maximum sheath temperature = 1200°F (649°C)
• Maximum outlet temperature = 750°F (399°C)

Options Watlow
Part Number Description
Terminal Enclosures
Replacement Modules
Terminal enclosures are available in general purpose and M63 6kW, 240V, 3 phase
moisture resistant configurations. M610 6kW, 240V, 1 phase
M65 6kW, 480V, 3 phase
High-Limit Thermocouples
M611 6kW, 480V, 1 phase
High-limit thermocouples can be supplied on specified
High Limit Thermocouple Kits
modules or shipped as a kit. Available thermocouples are
MTCJ Type J (0-1000°F)
Types J and K.
MTCK Type K (0-2000°F)
Blank Module Covers Blank Module Covers
Module covers are available for covering blank slots on MBLK Cover slots in main flange
the main flange. This allows for adding heater modules at
a later time to allow higher wattage outputs.

Replacement Modules
Replacement modules provide easy field service and
reduce downtime. To order replacement modules
specify the replacement module part number (from the
table), then specify the quantity.

392
Air Heaters
Finned Heaters
375 Finned Strip Heaters
Watlow’s 375 finned strip heater is constructed of
highly-compacted magnesium oxide (MgO) based
insulation, which conducts heat efficiently from the
nickel chromium element wire to the sheath. Two-inch
wide (51 mm) nickel plated fins are attached to maximize
surface contact allowing heat to transfer into the air
faster. Lower sheath temperature and element life are
maximized by this finned construction.

Performance Capabilities
• Aluminized steel sheath temperatures up to
1100°F (595°C)
• Watt density up to 33 W/in2 (5.1 W/cm2)
• UL® approved up to 240VAC (File No. E52951)
• CSA approved up to 480VAC (File No. LR7392)

Features and Benefits Aluminized Steel Sheath

Nickel chromium element wire is centered in the (Optional 430 SS Sheath)
heater Nickel
Plated Fins
• Ensures temperature uniformity (Optional
430 SS Sheath)
Aluminized steel sheath Nickel Chromium
• Operates at higher temperatures Resistance Wire
• Resists corrosion more effectively than iron-sheathed
MgO Insulation
heaters
Optional 430 stainless steel sheath
• Provides a durable solution for highly-corrosive Welded 10-24
environments Threaded Post Terminals

Welded post terminals

• Produces strong, trouble-free connections
Available lengths from 51/2 to 48 in. Typical Applications
(140 to 1220 mm) • Enclosure heating
• Fits a variety of application needs • Load bank resistors
• Shrink tunnels
• Duct heaters
• Space heaters
• Drying ovens
• Incubators
• Air heating
• Heat curing
• Ink drying
• Food warmers
• Moisture protection
• Dehumidifiers
• Stress relieving ovens

393
Air Heaters
Finned Heaters
375 Finned Strip Heaters
Applications and Technical Data
Calculating Watt Density Formulas
Use the graph and formulas to ensure that the Wattage
maximum allowable watt density for the heater is Watt Density =
not exceeded in the application. Heated Area

Open air watt density is calculated for the total heated Heated Area
surface area. (Offset Terminals) = [Overall Length (A) - 4 in.]
x 3.75 in.
= [Overall Length (A) - 102 mm]
x 95.3 mm
Heated Area
(Parallel Terminals) = [Overall Length (A) - 3.12 in.]
x 3.75 in.
= [Overall Length (A) - 79.3 mm]
x 95.3 mm
Heated Area
(One-on-One Terminals) = [Overall Length (A) - 4.25 in.]
x 3.75 in.
= [Overall Length (A) - 108 mm]
x 95.3 mm

Maximum Allowable Watt Density

Watt Density—W/cm2
1 2 3 4 5
600
300
15 ft/sec (4.6 m/sec) Air Speed
500 10 ft/sec (3.0 m/sec) Air Speed
5 ft/sec (1.5 m/sec) Air Speed
Ambient Air Temperature—°F

Ambient Air Temperature—°C

400 Still Air 200

300

200 100

100

0
0 5 10 15 20 25 30
Watt Density—W/in2

0 ft/sec (0 m/sec) Air Speed

394
 (30 mm) 13⁄8 in.
(34.9 mm)
7⁄8 in. 3⁄8 in.
(22.2 mm) (9.5 mm)
A

1⁄2 in.
(13 mm)
3⁄8 in. 11⁄2 in.

Air Heaters
5⁄16 x 1⁄2 in. (7.9 x 13 mm)
(9.5 mm) (38 mm)
Mounting Slots

11⁄2 in. 3⁄4 in. 2 in.

(38 mm) (19 mm) (50.8 mm)

Finned Heaters
17⁄8 in. Heated Length 11⁄4 in.
(47.6 mm) (32 mm)
375 Finned Strip Heaters Typ.

Termination Options
Offset Terminals One-on-One Terminals
10-24 Threaded Terminals 10-24 Threaded Terminals

1.18 in. 1.18 in.

13⁄8 in.
(30 mm) (30 mm) 13⁄8 in.
(34.9 mm)
7⁄8 in. (34.9 mm)
3⁄8 in.
(22.2 mm) 3⁄8 in.
7⁄8 in. (9.5 mm)
(22.2 mm)
(9.5 mm)
A
0.950 in.
(24.1 mm)
7⁄810-24
in. Threaded Terminals 1⁄2 in. A

(13 mm) Heated Length

3⁄8 in. 11⁄2 in. (22.2 mm) 5⁄16 x 1⁄2 in. (7.94 x 13 mm)
3⁄8 in. 5⁄16 x 1⁄2 in. (7.9 x 13 mm)
1.18 in. (38 mm) (9.5 mm) 11⁄2 in. 1⁄2 in.
(9.5 mm) 13⁄8 in. Mounting Slots
(30 mm) Mounting Slots (38 mm) (13 mm)
(34.9 mm)
3⁄8 in.
7⁄8 in. (9.5 mm)
2 in. 11⁄2 in. 2 in.
11⁄2 in. 3⁄4 in. (22.2 mm)
(38 mm) (19 mm) A (50.8 mm) (38 mm) (50.8 mm)
7⁄8 in. 1⁄2 in.
(13 mm)
3⁄8 in. 11⁄2 in. (22.2 mm) 5⁄16 x 1⁄2 in. (7.94 x 13 mm)
3
(9.5 mm) (38 mm)2 ⁄4 in. Heated Length 11⁄4 in. C
(70 mm) Mounting Slots (32 mm) B 1⁄2 in.
Typ.
(13 mm)
11⁄2 in. 3⁄4 in. 2 in.
(38 mm) (19 mm) (50.8 mm)
Two 10-24 threaded post terminals are offset from each Two 10-24 threaded post terminals are placed one on
other on the (702same
3⁄4 in.
mm)
end. Heated Length 11⁄4 in. each end.
(32 mm)
10-24 Threaded Terminals Typ.

1.18 in.
(30 mm) 13⁄8 in.
(34.9 mm)
Parallel Terminals 7⁄8 in.
(22.2 mm)
3⁄8 in.
(9.5 mm)
In-Line Terminals
A
10-24 Threaded Terminals 1⁄2 in. 10-24 Threaded Terminals
(13 mm)
1.18 in. 3⁄8 in. 11⁄2 in. 5⁄16 x 1⁄2 in. (7.9 x 13 mm) 1.18 in.
(30 mm) (9.5 mm) (38 mm) 13⁄8 in. (30 mm) 13⁄8 in.
Mounting Slots (34.9 mm) (34.9 mm)
7⁄8 in. 3⁄8 in. 7⁄8 in. 3⁄8 in.
(22.2 mm) (9.5 mm) (22.2 mm) (9.5 mm)
11⁄2 in. 3⁄4 in. 2 in. A
A
(38 mm) (19 mm) (50.8 mm)
7⁄8 in. 1⁄2 in.
1⁄2 in. 11⁄2 in.
(13 mm) (38 mm) (22.2 mm) (13 mm)
3⁄8 in. 11⁄2 in. 5⁄16 x 1⁄2 in. (7.9 x 13 mm) 3⁄8 in. 5⁄16 x 1⁄2 in. (7.94 x 13 mm)
(9.5 mm) 17⁄8 in.
(38 mm) Heated SlotsLength 11⁄4 in. (9.5 mm) Mounting Slots
(47.6 mm) Mounting
(32 mm)
Typ. 3⁄4 in.
(19
2 in. mm) 2 in.
11⁄2 in. 3⁄4 in. 11⁄2 in. (50.8 mm)
(38 mm) (19 mm) (50.8 mm)
(38 mm)

17⁄8 in. 23⁄4 in. Heated Length 11⁄4 in.

Heated Length 11⁄4 in. (70 mm) (32 mm)
(47.6 mm) (32 mm) Typ.
Typ.

10-24 Threaded Terminals

Two 10-24 threaded post terminals are used; both

1.18 in.
(30 mm) 13⁄8 in.
Two 10-24 threaded post terminals are in-line with each
terminals on one end. 7⁄8 in.
(22.2 mm) 3⁄8 in.
(34.9 mm)
other on the same end.
(9.5 mm)
0.950 in.
(24.1 mm)
10-24 Threaded Terminals
A

Heated Length
1.18 in. 3⁄8 in. 5⁄16 x 1⁄2 in. (7.9 x 13 mm)
(30 mm)(9.5 mm) 11⁄2 in. 1⁄2 in.
Mounting Slots 13⁄8 in.
(38 mm) (13 mm)
(34.9 mm)
7⁄8 in.
(22.2 mm) 3 ⁄8 in.
(9.5 mm)
11⁄2 in. 0.950 in. 2 in.
(38 mm) (24.1 mm) (50.8 mm)
A

3⁄8 in. Heated Length 5⁄16 x 1⁄2 in. (7.9 x 13 mm)

(9.5 mm) 11⁄2 in. 1⁄2 in.
Mounting Slots
(38 mm) (13 mm) C

B 1⁄2 in.
(13 mm)
11⁄2 in. 2 in.
(38 mm) (50.8 mm)

B 1⁄2 in.
(13 mm)

395
 Air Heaters
Finned Heaters
375 Finned Strip Heaters
Termination Options (Continued)
Metallic Terminal Boxes - Variations
2½ in. (64 mm) 2½ in. (64 mm)
Metallic terminal boxes are available from 0.020 stock on offset
Tk. 5 Fins Per Inch
terminals. Terminal 11/2" boxes
7/8"
(38.1 mm) (22.2 mm)
act as a safety feature by
covering the terminals. A conduit may be attached to the
" (9.5 mm) 7/8 in. (22.2 mm) diameter holes in the ends
box3/8through 2 in. (51 mm)
11/2" 3 "
(38.1of
mm)the/4 box. To order, specify terminal box. 2"
(19 mm) (50.8 mm)

2 in. (51 mm) 1½ in. (38 mm)

/
1 2" (12.7 mm)

/ /
5 16" x 1 2" Typ.
(7.9 mm x 12.7 mm)
Mtg. Holes 2 3/4" Heated Length 11/4"
Available on offset terminals from stock
(69.8 mm) (31.7 mm) and manufactured.
Typ.
2 in. (51 mm) A

10-24 Threaded Terminals

7/8"
(22.2 mm)
13/8"
(34.9 mm)
Available on in-line terminals only. /
3 8"
(9.5 mm)
/
7 8"

(22.2 mm)
Typ.

Accessories
Secondary Insulation Bushings Ceramic Terminal Covers

15/8 in.
(41.3 mm) / in. (9.5 mm)
3 8

/
1 4 in.-20 x 11/2 in. Threaded Length Screw

/
1 8 in. (3.2 mm)

/
3 8 in. (9.5 mm)

Ceramic terminal covers offer a convenient and

economical method to insulate post terminals. A 10-24
screw thread is sized for standard length posts and is
Insulators are suitable when air heating and/or voltage to supplied as an accessory item and shipped separately.
ground is a concern. A secondary insulation bushing kit, Specify Z-4918 and quantity.
part number Z-5230, contains one set of bushings for
one heater. To accommodate bushings, 17/32 x 11/16 inch
diameter mounting holes must be specified when
ordering.

Note: Number of fins are dependent on length of heater.

396
Air Heaters
Finned Heaters
375 Finned Strip Heaters
Heater Part Numbers
Width Length Power W/in2 Approx. Net Wt. Part
in. (mm) Termination in. (mm) Volts (Watts) (W/cm2) lbs (kg) Number
11/2 (38) Parallel 51/2 (140) 120 125 14 (2.1) 0.5 (0.23) SGA1J5JY2
Parallel 51/2 (140) 120 250 28 (4.3) 0.5 (0.23) SGA1J5JY3
Parallel 61⁄2 (152) 120 150 14 (2.1) 0.5 (0.23) SGA1J6AY1
Parallel 61⁄2 (152) 240 150 14 (2.1) 0.5 (0.23) SGA1J6AY2
Parallel 61⁄2 (152) 120 300 28 (4.3) 0.5 (0.23) SGA1J6AY3
Parallel 61⁄2 (152) 240 300 28 (4.3) 0.5 (0.23) SGA1J6AY4
Offset 71/2 (191) 120 150 12 (1.8) 0.7 (0.32) SGA1J7JW1
Offset 71/2 (191) 240 150 12 (1.8) 0.7 (0.32) SGA1J7JW2
Offset 71/2 (191) 240 200 15 (2.3) 0.7 (0.32) SGA1J7JW3
Offset 81⁄2 (203) 120 150 10 (1.5) 0.7 (0.32) SGA1J8AW2
Offset 81⁄2 (203) 240 150 10 (1.5) 0.7 (0.32) SGA1J8AW3
Offset 81⁄2 (203) 120 175 12 (1.8) 0.7 (0.32) SGA1J8AW4
Offset 81⁄2 (203) 240 175 12 (1.8) 0.7 (0.32) SGA1J8AW5
Offset 81⁄2 (203) 120 250 17 (2.6) 0.7 (0.32) SGA1J8AW6
Offset 81⁄2 (203) 240 250 17 (2.6) 0.7 (0.32) SGA1J8AW7
Offset 81⁄2 (203) 120 400 27 (4.2) 0.7 (0.32) SGA1J8AW8
Offset 81⁄2 (203) 240 400 27 (4.2) 0.7 (0.32) SGA1J8AW9
Offset 81⁄2 (203) 120 500 33 (5.1) 0.7 (0.32) SGA1J8AW10
Offset 81⁄2 (203) 240 500 33 (5.1) 0.7 (0.32) SGA1J8AW11
Offset 101/2 (267) 120 250 10 (1.5) 0.9 (0.40) SGA1J10JW1
Offset 101/2 (267) 240 250 10 (1.5) 0.9 (0.40) SGA1J10JW2
Offset 101/2 (267) 120 350 14 (2.1) 0.9 (0.40) SGA1J10JW3
Offset 101/2 (267) 240 350 14 (2.1) 0.9 (0.40) SGA1J10JW4
Offset 101/2 (267) 120 400 16 (2.5) 0.9 (0.40) SGA1J10JW5
Offset 101/2 (267) 240 400 16 (2.5) 0.9 (0.40) SGA1J10JW6
Offset 121⁄2 (305) 120 250 8 (1.2) 1.0 (0.45) SGA1J12AW1
Offset 121⁄2 (305) 240 250 8 (1.2) 1.0 (0.45) SGA1J12AW2
Offset 121⁄2 (305) 120 350 12 (1.8) 1.0 (0.45) SGA1J12AW3
Offset 121⁄2 (305) 240 350 12 (1.8) 1.0 (0.45) SGA1J12AW4
Offset 121⁄2 (305) 120 500 17 (2.6) 1.0 (0.45) SGA1J12AW5
Offset 121⁄2 (305) 240 500 17 (2.6) 1.0 (0.45) SGA1J12AW6
Offset 141⁄2 (356) 120 300 8 (1.2) 1.2 (0.54) SGA1J14AW1
Offset 141⁄2 (356) 240 300 8 (1.2) 1.2 (0.54) SGA1J14AW2
Offset 141⁄2 (356) 120 500 13 (2.0) 1.2 (0.54) SGA1J14AW3
Offset 141⁄2 (356) 240 500 13 (2.0) 1.2 (0.54) SGA1J14AW4
Offset 151/4 (387) 120 325 8 (1.2) 1.4 (0.64) SGA1J15EW1
Offset 151/4 (387) 240 325 8 (1.2) 1.4 (0.64) SGA1J15EW2
Offset 151/4 (387) 240 500 12 (1.8) 1.4 (0.64) SGA1J15EW3
CONTINUED

Note: 375 finned strip heaters with one-on-one terminations are available as a manufactured item only. Please contact your Watlow
representative for additional information.
Note: Above heaters are modified stock and may not be returned for a restocking charge.
Note: 5/16 x 1/2 in. (7.9 x 13 mm) mounting holes are supplied on all 375 finned strip heaters as standard, larger mounting holes may be
provided 17/32 in. x 11/16 in. (13.5 mm x 17.5 mm).
Note: Heaters can be customized given a business case review. Contact the factory for details.

397
Air Heaters
Finned Heaters
375 Finned Strip Heaters
Heater Part Numbers (Continued)
Width Length Power W/in2 Approx. Net Wt. Part
in. (mm) Termination in. (mm) Volts (Watts) (W/cm2) lbs (kg) Number
11/2 (38) Offset 177/8 (454) 120 350 8 (1.2) 1.6 (0.73) SGA1J17RW1
Offset 177/8 (454) 240 350 8 (1.2) 1.6 (0.73) SGA1J17RW2
Offset 177/8 (454) 120 375 9 (1.4) 1.6 (0.73) SGA1J17RW3
Offset 177/8 (454) 240 375 9 (1.4) 1.6 (0.73) SGA1J17RW4
Offset 177/8 (454) 120 500 12 (1.8) 1.6 (0.73) SGA1J17RW5
Offset 177/8 (454) 240 500 12 (1.8) 1.6 (0.73) SGA1J17RW6
Offset 177/8 (454) 120 750 18 (2.8) 1.6 (0.73) SGA1J17RW7
Offset 177/8 (454) 240 750 18 (2.8) 1.6 (0.73) SGA1J17RW8
Offset 177/8 (454) 120 1000 24 (3.7) 1.6 (0.73) SGA1J17RW9
Offset 177/8 (454) 240 1000 24 (3.7) 1.6 (0.73) SGA1J17RW10
Offset 191/2 (495) 240 350 6 (.9) 1.7 (0.77) SGA1J19JW2
Offset 191/2 (495) 120 500 9 (1.4) 1.7 (0.77) SGA1J19JW3
Offset 191/2 (495) 240 500 9 (1.4) 1.7 (0.77) SGA1J19JW4
Offset 191/2 (495) 240 750 13 (2.0) 1.7 (0.77) SGA1J19JW5
Offset 191/2 (495) 240 1000 17 (2.6) 1.7 (0.77) SGA1J19JW6
Offset 211⁄2 (533) 120 500 8 (1.2) 1.9 (0.86) SGA1J21AW3
Offset 211⁄2 (533) 240 500 8 (1.2) 1.9 (0.86) SGA1J21AW4
Offset 211⁄2 (533) 120 750 12 (1.8) 1.9 (0.86) SGA1J21AW5
Offset 211⁄2 (533) 240 750 12 (1.8) 1.9 (0.86) SGA1J21AW6
Offset 233/4 (603) 240 500 7 (1.0) 2.1 (0.95) SGA1J23NW3
Offset 233/4 (603) 240 750 10 (1.5) 2.1 (0.95) SGA1J23NW5
Offset 233/4 (603) 120 1000 14 (2.1) 2.1 (0.95) SGA1J23NW6
Offset 233/4 (603) 240 1000 14 (2.1) 2.1 (0.95) SGA1J23NW7
Offset 233/4 (603) 240 1500 20 (3.1) 2.1 (0.95) SGA1J23NW8
Offset 251/2 (648) 120 500 6 (0.9) 2.3 (1.00) SGA1J25JW2
Offset 251/2 (648) 240 500 6 (0.9) 2.3 (1.00) SGA1J25JW3
Offset 251/2 (648) 120 750 9 (1.4) 2.3 (1.00) SGA1J25JW4
Offset 251/2 (648) 240 750 9 (1.4) 2.3 (1.00) SGA1J25JW5
Offset 251/2 (648) 240 1000 12 (1.8) 2.3 (1.00) SGA1J25JW6
Offset 263/4 (680) 240 700 8 (1.2) 2.4 (1.10) SGA1J26NW2
Offset 263/4 (680) 240 1000 12 (1.8) 2.4 (1.10) SGA1J26NW3
Offset 301/2 (775) 120 750 8 (1.2) 2.7 (1.20) SGA1J30JW1
Offset 301/2 (775) 240 750 8 (1.2) 2.7 (1.20) SGA1J30JW2
Offset 331/2 (851) 240 750 7 (1.0) 3.0 (1.40) SGA1J33JW1
Offset 357/8 (911) 120 1000 8 (1.2) 3.2 (1.50) SGA1J35RW1
Offset 357/8 (911) 240 1000 8 (1.2) 3.2 (1.50) SGA1J35RW2
Offset 357/8 (911) 240 1500 13 (2.0) 3.2 (1.50) SGA1J35RW3
Offset 381/2 (978) 120 1000 8 (1.2) 3.4 (1.50) SGA1J38JW2
Offset 381/2 (978) 240 1500 11 (1.7) 3.4 (1.50) SGA1J38JW3
Offset 421/2 (1080) 240 1500 10 (1.5) 3.8 (1.70) SGA1J42JW1
Offset 477/8 (1216) 240 2250 16 (2.4) 4.3 (2.00) SGA1J47RW2
Note: 375 finned strip heaters with one-on-one terminations are available as a manufactured item only. Please contact your Watlow representative
for additional information.
Note: Above heaters are modified stock and may not be returned for a restocking charge.
Note: 5/16 x 1/2 in. (7.9 x 13 mm) mounting holes are supplied on all 375 finned strip heaters as standard, larger mounting holes may be
provided 17/32 in. x 11/16 in. (13.5 mm x 17.5 mm).

398
Air Heaters
Finned Heaters
FINBAR™ Single-Ended Heaters
Composed of aluminized steel fins press fitted to a
one-inch single-ended FIREBAR element. The FINBAR™
is designed to improve heat transfer to the air and per-
mits putting more power in tighter spaces—like forced air
ducts, dryers, ovens and load bank resistors.
Heat transfer, lower sheath temperature and element life
are all maximized by its finned construction. Installation
is simplified by terminations exiting at one end and
mounting accommodations on both ends.

Performance Capabilities
• Watt densities up to 50 W/in2 (7.7 W/cm2)
• 304 stainless steel sheath temperatures up to
1200°F (650°C)
• Voltages up to 480VAC
Flexible Lead Wires
• Amperages up to 48 amperes per heater or
16 amperes per coil Aluminized Steel Fins

SS Mounting Bracket
Features and Benefits Slotted End 304 SS Sheath
Rugged aluminized steel fins
• Provides an increase in surface area to approximately
16 square inches for every linear inch of element
length. Fins press fitted to the heating element
improve heat transfer to the air Typical Applications
Single-ended termination • Forced air heating for dryers, ovens, ducts
• Simplifies wiring and installation • Still air heating for ovens, comfort heating
Stainless steel mounting bracket, welded to the • Incubators
terminal end, supplied with a slotted end
• Ink drying
• Allows ease of installation
• Load bank resistors
Lavacone seals
• Provides protection against humid storage
conditions, moisture retardant to 221°F (105°C)

For detailed product and technical data,

see the full FINBAR product
section located on pages 103 through 105.
399
Air Heaters
FIREROD® CARTRIDGE Heaters
The Watlow® FIREROD® cartridge heater incorporates
engineering excellence and is supported by over
60 years of solid industry performance across a broad
range of simple and complex applications. As the
premier choice in swaged cartridge heating, thousands
of industrial manufacturers continue to choose Watlow
as their trusted thermal partner and certified cartridge
heater supplier.
Built using premium materials and tight manufacturing
controls, the FIREROD heater provides superior heat
transfer, uniform temperatures, resistance to oxidation
and corrosion and a long life even at high temperatures.
Every system component that leaves our manufacturing
facilities meets our strict quality assurance specifications,
in addition to those set forth by leading standards and
regulating industries.
To meet our customer’s individual needs, there are many
delivery options available for FIREROD heaters. Sheath
Conductor
Performance Capabilities Pins
MgO
• Part temperatures up to 1400°F (760°C) on Insulation
alloy 800 sheath End Piece

• Watt densities up to 400 W/in2 (62 W/cm2) Lead Wires

Resistance Wire
• Maximum voltage up to 480V

Features and Benefits t

Nickel-chromium resistance wire Hea
No tion
• Ensures even and efficient distribution of heat to Sec
the sheath
Metalurgically-bonded conductor pins
• Ensures a trouble-free electrical connection
Magnesium oxide insulation of specific grain and International Organization for Standardization (ISO)
purity 9001 certified
• Results in high dielectric strength and contributes to • Provides confidence that quality and reliability
faster heat-up expectations are met
Alloy 800 sheath UL® and CSA approved flexible stranded wires
• Resists oxidation and corrosion from heat, many • Lead insulation rated to temperatures up to
chemicals and atmospheres 840°F (450°C)
Minimal spacing between the element wire and Patented lead adapter (LA) method
sheath • Allows same day shipment on more than 150,000
• Results in lower internal temperature configurations of stock FIREROD heaters and lead
• Accommodates a design with fewer or smaller heaters combinations
operating at higher watt densities

For detailed product and technical data,

see the full FIREROD product
section located on pages 9 through 44.
400
Air Heaters
Enclosure Heaters
WATROD™ Heaters
Designed to prevent freezing and condensation in
electrical and mechanical enclosures, the WATROD™
element is enclosed in a perforated, aluminized-steel
bracket.

Performance Capabilities
• Watt densities up to 15 W/in2 (2.3 W/cm2)
• Wattages up to 1000 watts
• UL® and CSA component recognition up to 250VAC
TUBULAR ENCL 4
Features and Benefits
Stainless steel sheath wall
• Resists corrosion and protects the heating coil
from exposure
Silicone resin seal
• Provides protection against humid storage conditions
and is effective to 390°F (200°C)
Perforated aluminized-steel mounting bracket 0.315 in. (8 mm) Dia.
Element
Main Bracket

• Eases installation and helps prevent direct contact

with the heating element
Stock straight projection Type B #10-32 screw lug
terminals 3½ in.
(89 mm)
• Provides easy electrical connection
Made-to-order threaded stud
• Provides quick connect and flexible lead wire
termination options 1 in. 7 in.
(25 mm) (178 mm)
7⁄16 in.
Typical Applications 1½ in.
(38 mm)
(11.1 mm)
85⁄16 in.
(211.1 mm)

• Control panels
• Traffic signal boxes
• Automated teller machines
• Switch gear
• Electronic equipment

Application Hints
• Locate heater(s) in the lowest portion of the enclosure
to maximize convection heating
• Place thermostat(s) in the upper half of the enclosure,
away from the heater(s)

401
Air Heaters
Enclosure Heaters
WATROD Heaters
Technical Heaters
Watt
Density Part Number Est. Net Wt.
Watts W/in2 (W/cm2) 125VAC 250VAC lbs (kg)
95 4 (0.6) EN951 1.5 (0.7)
100 4 (0.6) EN10010 1.5 (0.7)
250 10 (1.6) EN2501 EN25010 1.5 (0.7)
375 15 (2.3) EN3751 EN37510 1.5 (0.7)

402
Air Heaters
Enclosure Heaters
Silicone Rubber Heaters
Designed for freeze and condensation protection, Watlow’s
enclosure heaters are rugged, reliable and safe to
operate. These rectangular-shaped, wire-wound silicone
rubber heaters can be ordered individually with adhesive or
vulcanized to an aluminum mounting plate. A thermostat
can be attached to the heater or mounted separately
as shown.

Performance Capabilities
• Watt density rating of 5 W/in2 (0.8 W/cm2)
• Temperature up to 150°F (66°C)

Features and Benefits

Pressure-sensitive adhesive mounting to an
aluminum plate or customer cementing
• Reduces installation time
• Creates easy installation
Element Vulcanized
Several standard thermostat set points Between Two Layers of
• Ensures protection against freezing with minimal Silicone Rubber/Fiberglass
energy consumption
Variety of installation options 0.055 in. (1.4 mm)
• Provide the option to utilize cement installation to Thick Heater
With Wire-Wound
ensure permanent heater attachment Element
• The pressure sensitive adhesive installation option Optional Mounting Plate
With Heater On Side
saves assembly time PTFE, Silicone, or
Opposite Flange
Neoprene-Insulated
• Facilitate assembly and disassembly with factory Leads Available Optional Thermostat
installed aluminum plate mount Mounted to Heater

Remote thermostat option

• Provides optimal choice of heater location versus Typical Applications
temperature control location Freeze or condensation prevention in housings
Lead options containing electronic equipment including:
• Allows for a variety of applications • Traffic signal boxes
• Allows different lead lengths for a variety of wiring • Automated teller machines
requirements
• Temperature control panels
Factory pre-wired heater and thermostat
• Ensures safety and reliability as there are no • Gas or liquid control valve housings
exposed electrical connections

403
 Air Heaters
Enclosure Heaters
Silicone Rubber Heaters
Options
Aluminum Mounting Plate Heater
Both vertical and horizontal mounting can be Width

accomplished with enclosure heaters. Mounting plates 1/2 in.

(13 mm)
are 0.040 in. (1.02 mm) thick, specified as #3003 H14 7/32 x 1/2 in.

(5.6 x 13 mm)
aluminum. The preferred orientation is vertical with a Slot Typ.
thermostat attached at the lower end (as shown in the
drawing).
7/32 x 1/2 in.
For horizontal mounting, a remote thermostat is
(5.6 x 13 mm)
recommended.
Slot Typ. An enclosure heater can be ordered by
0.040 in. (1.02 mm)
itself, with PSAS or vulcanized to an aluminum mounting Aluminum

5 in. (127 mm) Typ.

Heater Length
plate. See the Thermostat section below for more

See Note ①
information.
0.065 in. (1.7 mm) 1/2
Heater 0.53 in
0.040 in. (1.02 mm)
0.75
Aluminum
5 in. (127 mm) Typ.
See Note

See Note ②
0.065 in. (1.7 mm) 1/2 in. (13 mm) 1.25 in.

(64 mm) Typ.

0.75 in.
Heater (32 mm)
0.53 in. (13.5 mm) (19 mm)

2.5 in.
0.75 in. (19 mm)

/
1 2 in.
¿ ① 4 in. (102 mm) on
(13 mm)
(64 mm) Typ.

5 in. (127 mm) unit.

See Note

¡ ② 0.5 in. (13 mm) on

2.5 in.

5 in. (127 mm) unit.

Thermostats
Mounted on Heater Notes:
Built-in snap action thermostats from Watlow sense air • On both integral and remote sensors, the thermostat’s
temperature. See the ordering chart on the following exposed metal cap is vulnerable to impact. This could
page for available settings. defeat the thermostat’s switching action and cause
heater malfunction.
Remote From Heater
• T-10 thermostats are not recommended for enclosure
For an air sensing thermostat that is separate from the heating applications.
heater, the ST-207E is ideal. It is a modified ST-207
mounted on a 1/32 in. (0.8 mm) thick G-10 circuit board
with the thermostat’s metal cap exposed to sense air
temperature. The thermostat is placed at the midpoint
of the lead length. The sensor can be preset at the
temperatures listed for integral sensors.

404
Air Heaters
Enclosure Heaters
Silicone Rubber Heaters
Technical Data
Determining Minimum Wattage Requirements
For Enclosures
This chart is an excellent guide for determining total For windy conditions, add an additional 50 percent to
wattage requirements for both insulated and uninsulated the wattage requirement listed.
enclosures, assuming the box is relatively airtight.

Total Enclosure Surface Area — Square Feet (Square Meters)

2 3 4 5 6 7.5 9 10 15 20 25 30 40 50
(0.2) (0.3) (0.4) (0.5) (0.6) (0.7) (0.8) (0.9) (1.4) (1.9) (2.3) (2.8) (3.7) (4.7)

20 30 40 55 70 80 100 120 135 205 270 335 405 540 670

Temperature Rise from Ambient °F (°C)

(11) 10 10 15 20 20 25 30 35 50 65 80 100 130 160

40 55 80 110 135 160 200 245 270 405 540 670 805 1075 1340
(22) 15 20 30 35 40 50 60 65 100 130 160 195 260 320
60 90 120 160 205 245 300 365 405 605 805 1005 1210 1610 2010
(33) 20 30 55 50 60 75 90 100 145 195 240 290 385 480
80 110 160 215 270 325 400 485 540 805 1075 1340 1610 2145 2680
(44) 30 40 55 65 80 100 115 130 195 260 320 385 515 640
100 135 200 270 335 405 500 605 670 1005 1340 1675 2010 2680 3350
(56) 35 50 65 80 100 125 145 160 240 320 400 480 640 800
120 165 240 320 405 485 600 725 805 1210 1610 2010 2415 3220 4020
(67) 40 60 80 100 115 150 175 195 290 385 480 580 770 960
140 190 280 375 470 565 700 845 940 1410 1880 2345 2815 3755 4690
(78) 45 70 90 115 135 175 205 225 340 450 560 675 900 1120

Uninsulated boxes Insulated boxes

Silicone Rubber Enclosure Heaters Offering

For a complete list of silicone rubber product offerings
available for use as an enclosure heater with a thermostat,
please refer to the offerings on page 119.

405
Air Heaters
FLUENT® In-line Heaters

Watlow’s FLUENT® in-line fluid heater is a small,

lightweight, high-performance heater that can replace
both a traditional immersion type heater or a heater
wrapped around a tube as part of a thermal system.
Watlow’s FLUENT heater is designed as an integrated
solution that replaces multiple components in a system.
This heater design reduces overall system cost and
complexity. Because of its high watt density, it offers
ultra-fast response leading to higher system performance.
Featuring Watlow’s patented layered heater technology,
the heater makes use of its entire surface to produce
heat, which optimizes heat transfer and temperature
uniformity.

Features and Benefits

Small, lightweight, robust heater construction
• Replaces multiple components in a system
• Reduces overall system size
• Lowers total cost of ownership
Patented circuit patterning process
• Facilitates customizable heating profiles Typical Applications
• Enables distributed wattage and/or multiple zones • Hemodialysis fluid heating
• Assures precise and repeatable power distribution • Food cooking equipment
High watt density, low mass heater • Semiconductor purge and carrier gas heating
• Contributes to fast response time • Ink preheating systems
• Allows for efficient heat transfer • On-demand fluid heating
• Enables on-demand process start-up

For detailed product and technical data,

see the full FLUENT in-line product
section located on pages 445 through 448.

406