Process air duct heaters are used for tempering forced
air in many industrial processes. Heater wattage is
dependent on air outlet temperature (up to 1200°F
[650°C]) and air velocity. Smaller duct heaters can be
tandem mounted in place of one large unit to meet
space limitations and simplify installation.
Heavy wall Incoloy tubular heating elements (field
replaceable) provide protection against corrosive air
environments and resistance to vibration when compared to open coil elements.
®
Air duct heaters can be designed specifically for high
pressure and/or hazardous locations. Turnkey systems
including the duct heater, power and temperature control panel, and the temperature and over-temperature
sensors can also be provided.
Our creative team of professionals can design and
manufacture your next process forced air duct
heating system.
Consult us with Your Requirements.
Typical Applications
➻ Air Drying/Curing
➻ Annealing
➻ Autoclaves
➻
Booster Air Heater
Operations
➻
Breaking Resistor
➻ Core Drying
➻ Dehumidification
➻ Forced Air Comfort Heating
High Temperature Application:
The electrical housing is separated
from the heater flange to lower the
ambient temperature of the
electrical wiring.
Electrical Housings: NEMA 4
(moisture resistant), NEMA 7
(explosion resistant) and NEMA
12 (dust resistant) are available.
11-104
➻
Heat Treating
➻ Make-Up Air Heating
➻ Re-Heating
➻ Resistor Load Banks
Sealed Insulated Housing: An optional totally sealed
insulated housing prevents contamination from entering
the air stream. Shown is a stainless steel heater for a
medical product manufacturing application.
Element Configuration: Elements can
be U-bends, W-bends and foldback
design depending on the requirements
of the application.
Selection and Sizing
See Page 11-107
Installation and Wiring
See Page 11-111
Standard Designs
See Page 11-113
Companies that integrate
TEMPCO’s Forced Air Duct Heater Systems
have something in common:
One less thing to worry about.
Duct Heater System: Tempco can supply the heater and
blower assembled, ready for connection to the application
duct work. The pictured 48KW, 480V unit produces
1500 CFM of heated air to dry
metal parts after being coated
with a rust inhibitor.
Complete Your Thermal Loop System
with a Tempco Power/Temperature
Control Panel.
See pages 13-56 through 13-63.
(800) 323-6859 • Email: sales@tempco.com
11-105
Tubular Industrial Process
Duct Heaters
Forced Air Duct Heaters
A
NEMA 1 terminal box
enclosure with vented cover
to help keep wiring cooler.
Optional enclosures: NEMA 4
(moisture resistant), NEMA 7
(explosion resistant) and NEMA
12 (dust resistant).
B
3-1/2 inches (89 mm) of mineral
insulation in an aluminized steel
enclosure minimizes heat losses
while keeping the electrical
wiring cooler.
C
F
D
Standard field replaceable elements are held in
place with single-screw quick-release “V” clamps.
Optional: Gastight design utilizing welded
elements, compression fittings, or bulkhead fittings
to attach elements to the flange, preventing leakage
of ducted gases into the terminal enclosure.
Compression Fittings
11-106
E
The heavy duty frame is
composed of a 1/4 inch (6 mm)
thick steel mounting flange,
stainless steel support plate and
corner posts to securely hold the
heating elements rigid in any
mounting position.
The silicone resin sealed
elements are .430 inch (11 mm)
diameter with Incoloy® sheath
for excellent scaling and
corrosion resistance at high
temperatures. Element hairpin
bends are repressed in special
dies to re-compact the MGO
refractory to eliminate any
electrical insulation voids and
hot spots.
1/2" OD (12 mm) 3/8" ID (9 mm)
inside diameter thermowell
accessed through a 1/8" NPT
tapped hole in the flange allows
installation of an optional Type J
or K thermocouple for sensing the
element temperature. An excellent
safeguard for your system.
NOTE: Thermocouples (process
and high limit) can be clamped
directly to an element for faster
response.
Bulkhead Fittings
View Product Inventory @ www.tempco.com
Tubular Industrial Process
Duct Heaters
Checklist — Selecting the Proper Duct Heater
Sizing a Duct Heater
To properly match a duct heater to an application, the
wattage, air velocity and element watt density must be determined.
Formulas and graphs on the following pages that will aid
you in your design include:
• Wattage calculation formulas and table
• Element Watt Density vs. Sheath Temperature
and Air Velocity Graph
• Pressure Drop vs. Air Velocity Graph
In most applications the following design limitations
should be adhered to:
• Maximum watt density of 40 watts/in2 (6.2 watts/cm2)
• Maximum element sheath temperature of 1400°F (760°C)
• Minimum air velocity of 200 feet per minute
(61 meters per minute)
Calculating Minimum Wattage Requirement
Calculating Minimum Wattage Requirement
Table is for quick-estimation purposes and is based on air under
standard conditions (70°F inlet air temperature at 14.7 PSIA).
Note: If air flow is given in CFM at operating temperature and pressure it can be converted to SCFM
(Standard Cubic Feet per Minute) with the following formula (use the equations to the right
for compressed air):
P
530
SCFM = CFM × 14.7 × T + 460
For free air use equations:
KW =
3000
or
KW =
SCMM × Temperature rise (°C)
47
For compressed air use equations:
KW =
P = operating pressure (gauge pressure + 14.7)
SCFM × Temperature rise (°F)
CFM* × Density* (lbs/cu. ft.) × Temperature rise (°F)
228
or
KW =
T = operating temperature
Remember when calculating wattage
to use the maximum anticipated air
flow and to compensate for any heat losses.
CMM* × Density* (kgs/cu. m) × Temperature rise (°C)
57.5
*At heater inlet temperature and pressure
KWH to Heat Air at Selected Flow Rates
Amt. of Air
CFM
100
200
300
400
500
600
700
800
900
1000
1100
1200
50
100
150
200
1.7
3.3
5.0
6.7
8.3
10.0
11.7
13.3
15.0
16.7
18.3
20.0
3.3
6.7
10.0
13.3
16.7
20.0
23.3
26.7
30.0
33.3
36.7
40.0
5
10
15
20
25
30
35
40
45
50
55
60
6.7
13.3
20.0
26.7
33.3
40.0
46.7
53.3
60.0
66.7
73.3
80.0
Temperature Rise (°F)
250
300
350
400
Kilowatt Hours to Heat Air
8.3
16.7
25.0
33.3
41.7
50.0
58.3
66.7
75.0
83.3
91.7
100.0
10
20
30
40
50
60
70
80
90
100
110
120
11.7
23.3
35.0
46.7
58.3
70.0
81.7
93.3
105.0
116.7
128.3
140.0
(800) 323-6859 • Email: sales@tempco.com
13.3
26.7
40.0
53.3
66.7
80.0
93.3
106.7
120.0
133.3
146.7
160.0
450
500
600
15
30
45
60
75
90
105
120
135
150
165
180
16.7
33.3
50.0
66.7
83.3
100.0
116.7
133.3
150.0
166.7
183.3
200.0
20
40
60
80
100
120
140
160
180
200
220
240
Note: For additional
information or help with
your application please
consult TEMPCO.
11-107
Tubular Industrial Process
Duct Heaters
Checklist — Selecting the Proper Duct Heater, continued
Element Watt Density vs. Air Temperature and Air Velocity
Use graph (English or Metric) to plot
Outlet Air Temperature vs. Outlet Air Velocity to determine Element Watt Density
The recommended watt density is based on a maximum element sheath temperature of 1400°F (760°C). Air and
other gases that are poor conductors of heat require watt densities matched to the velocity of the gas flow to prevent
element overheating. Selecting a lower watt density for the heating elements will extend heater life expectancy.
Air Velocity (feet per minute)
English
Process Temperature °F — Approximate Sheath Temperature 1400°F
Air Velocity (meters per minute)
Metric
Process Temperature °C — Approximate Sheath Temperature 760°C
Element Watt Density is the wattage dissipated per square inch of the
element sheath surface and is calculated with the following formula.
Watt Density
11-108
=
π ×
element wattage
element dia. × element heated length
View Product Inventory @ www.tempco.com
Tubular Industrial Process
Duct Heaters
Checklist — Selecting the Proper Duct Heater, continued
Element Watt Density vs. Sheath Temperature and Air Velocity
Use graph (English or Metric) to plot
Watt Density vs. Air Velocity to determine Sheath Temperature
or
Watt Density vs. Sheath Temperature to determine the required Air Velocity
Watt Density (W/in2)
English
Sheath Temperature (°F)
Watt Density (W/cm2)
Metric
Sheath Temperature (°C)
(800) 323-6859 • Email: sales@tempco.com
11-109
Tubular Industrial Process
Duct Heaters
Checklist — Selecting the Proper Duct Heater, continued
Pressure Drop vs. Air Velocity
Use graph (English or Metric) to plot
Pressure Drop vs. Air Velocity for standard duct heaters sizes used to properly Size Blowers
Air Velocity (feet per minute)
English
Approximate Pressure Drop (inches of water)
Calculating Air Velocity
Velocity (feet/minute) =
SCFM (CFM measured at standard conditions)
Duct cross sectional area at heater in square feet
Air Velocity (meters per minute)
6
KW
er
at
He
r
eate
WH
12 K
W
18 K
ter
Hea
24-125
ater
KW He
Metric
Approximate Pressure Drop (Kilopascals)
11-110
View Product Inventory @ www.tempco.com
Tubular Industrial Process
Duct Heaters
Duct Heater Installation Recommendations
Installation Recommendations
1. Tempco Duct Heaters may be bolted to the ductwork through
the side, bottom or top. Bottom and side mounting are preferred
to minimize wiring/terminal enclosure temperatures.
2. Before mounting, consideration should be given to the strength
of the ductwork required to support the weight of the heater.
Add additional hangers or supports as required.
3. The inlet side of the unit should be at least 48 inches downstream from any change in duct size or duct direction.
4. To minimize pressure drop, mount the duct with the narrow
width of the heater perpendicular to the air flow.
5. Duct heaters may be mounted in tandem to increase the KW
that can be installed.
6. Process temperature sensing should be located downstream
from the duct heater.
7. Air flows must never be interrupted. Such events will cause
overheating and/or premature heater burnout. Your installation
should include high limit temperature controls. All standard
duct heaters have a thermowell attached to one element for
installing a thermocouple to sense element temperature.
Additional protection for the heater from low air flow can be
achieved by installing an air flow switch or pressure switch on
the inlet side.
8. Select the terminal housing that provides the best terminal protection from the environment surrounding the application.
Wiring
1. Power supply conductors must have a minimum ampacity of
125% of the maximum heater load and be rated for the ambient temperature of the heater enclosure.
2. The air handler should run on a time delay after the heater is
de-energized. This allows the elements to cool without overheating adjacent areas.
3. Duct heaters drawing more than 48 Amps are divided into
smaller branch circuits, each drawing 48 Amps or less. Please
note that the number of circuits, can be changed to accommodate any wiring requirements you may have.
Note: Before you proceed to make any changes on factory
prewired heaters, check the heater wiring schematic or consult Tempco.
All electrical wiring must be done in accordance with
national and local electrical codes.
Maintenance Recommendations
1. Never perform any type of service on duct heaters prior to
disconnecting all power supply lines.
2. After long periods of idle use, clean elements prior to start-up.
3. Periodically clean the elements even during regular use so as
not to allow dirt to build up on the elements.
(800) 323-6859 • Email: sales@tempco.com
4. Periodically check that mounting screws or bolts have not
become loose from blower vibration.
5. Periodically check that electrical connections are clean and
tight.
6. Failed elements are field replaceable, minimizing downtime
and saving the cost of a complete new heater.
11-111
Tubular Industrial Process
Duct Heaters
Standard Duct Heater Features
Design Features
✴ NEMA 1 General Purpose Ventilated Enclosure
✴ Painted Steel Mounting Flange
✴ Single- and Three-Phase Wiring
✴ 3-1/2 " (89 mm) Insulation
✴ Field Replaceable Incoloy® 840 Elements
✴ Element Bends Re-pressed
✴ 1/4" (6 mm) Inside Diameter Thermowell
✴ Stainless Steel Support Plate and Corner Posts
Typical Installation
Note: On Duct Heaters
having more than 54
heating elements, the
mounting flange thickness will
be increased from 1/4 to 3/8 of
an inch thick.
Standard (Non-Stock) Duct Heater Construction Specifications
Dimensions
Reference
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
11-112
“A”
277⁄8
277⁄8
277⁄8
277⁄8
277⁄8
277⁄8
277⁄8
277⁄8
277⁄8
277⁄8
327⁄8
403⁄8
493⁄8
in
708
708
708
708
708
708
708
708
708
708
835
1026
1254
mm
“B”
20
20
20
20
20
20
20
20
20
20
25
321⁄2
411⁄2
in
508
508
508
508
508
508
508
508
508
508
635
826
1054
mm
“C”
23⁄4
43⁄4
63⁄4
83⁄4
103⁄4
123⁄4
143⁄4
163⁄4
183⁄4
203⁄4
203⁄4
203⁄4
203⁄4
in
70
121
171
222
273
324
375
425
476
527
527
527
527
mm
“D”
61⁄2
81⁄2
101⁄2
121⁄2
141⁄2
161⁄2
181⁄2
201⁄2
221⁄2
241⁄2
241⁄2
241⁄2
241⁄2
in
165
216
267
318
368
419
470
521
572
622
622
622
622
mm
“E”
3
5
7
9
11
13
15
17
19
21
21
21
21
in
76
127
178
229
279
330
381
432
483
533
533
533
533
mm
“F”
35⁄8
55⁄8
75⁄8
95⁄8
115⁄8
135⁄8
155⁄8
175⁄8
195⁄8
215⁄8
215⁄8
215⁄8
215⁄8
in
“G”
92
143
194
244
295
346
397
448
498
549
549
549
549
mm
21⁄2
31⁄2
3
23⁄4
31⁄4
33⁄4
41⁄4
43⁄4
51⁄4
53⁄4
53⁄4
53⁄4
53⁄4
in
64
89
76
70
83
95
108
121
133
146
146
146
146
mm
Number
of
Elements
6
12
18
24
30
36
42
48
54
60
60
60
60
Approximate
Net Weight
lbs
kgs
22
31
41
51
62
73
84
95
106
117
130
155
180
10
14
19
23
28
33
38
43
48
53
59
70
82
View Product Inventory @ www.tempco.com
Tubular Industrial Process
Duct Heaters
Standard (Non–Stock) Duct Heaters
Watt
Density
W/in2 W/cm2
20
30
3.1
4.7
6
12
18
24
30
36
42
48
54
60
75
100
125
9
18
27
36
45
54
63
72
81
90
115
150
190
KW
Dimensions
Reference
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
1
2
3
4
5
6
7
8
9
10
11
12
13
Part Number
TDH01002
TDH01006
TDH01010
TDH01014
—
—
—
—
—
—
—
—
—
TDH01072
TDH01076
TDH01080
—
—
—
—
—
—
—
—
—
—
240V-1Ph
(1)
(1)
(2)
(2)
(C*)
(1)
(2)
(3)
TDH01003
TDH01007
TDH01011
TDH01015
TDH01018
TDH01021
TDH01024
TDH01027
TDH01030
TDH01033
TDH01036
—
—
TDH01073
TDH01077
TDH01081
TDH01084
TDH01087
TDH01090
TDH01093
TDH01096
TDH01099
TDH01102
TDH01105
—
—
240V-3Ph
(1)
(1)
(1)
(2)
(2)
(2)
(2)
(4)
(3)
(4)
(4)
(C*)
(1)
(1)
(2)
(2)
(5)
(3)
(7)
(4)
(6)
(5)
(10)
Part Number
Replacement
Elements
THE03405
THE03405
THE03405
THE03405
THE03405
THE03405
THE03405
THE03405
THE03405
THE03405
THE03845
—
—
THE03849
THE03849
THE03849
THE03849
THE03849
THE03849
THE03849
THE03849
THE03849
THE03849
THE03850
—
—
TDH01004
TDH01008
TDH01012
TDH01016
TDH01019
TDH01022
TDH01025
TDH01028
TDH01031
TDH01034
TDH01037
—
—
TDH01074
TDH01078
TDH01082
TDH01085
TDH01088
TDH01091
TDH01094
TDH01097
TDH01100
TDH01103
TDH01106
—
—
(1)
(1)
(1)
(1)
(2)
(2)
(2)
(2)
(3)
(4)
(4)
480V-1 Ph (C*)
(1)
(1)
(2)
(2)
(2)
(3)
(3)
(4)
(6)
(4)
(5)
TDH01005
TDH01009
TDH01013
TDH01017
TDH01020
TDH01023
TDH01026
TDH01029
TDH01032
TDH01035
TDH01038
TDH01039
TDH01040
TDH01075
TDH01079
TDH01083
TDH01086
TDH01089
TDH01092
TDH01095
TDH01098
TDH01101
TDH01104
TDH01107
TDH01108
TDH01109
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(2)
(2)
(2)
(2)
(4)
(4)
(1)
(1)
(1)
(1)
(2)
(2)
(2)
(2)
(3)
(4)
(4)
(4)
(5)
480V-3 Ph (C*)
Replacement
Elements
THE03819
THE03819
THE03819
THE03819
THE03819
THE03819
THE03819
THE03819
THE03819
THE03819
THE03846
THE03847
THE03848
THE03851
THE03851
THE03851
THE03851
THE03851
THE03851
THE03851
THE03851
THE03851
THE03851
THE03852
THE03853
THE03854
(C*) = Number of Branch Circuits per heater (48 amps each branch max). For different circuit wiring configurations consult Tempco.
Catalog Heaters
Order by catalog number for catalog
heaters.
Standard lead time is 3 to 4 weeks.
Note that Replacement Element Part
Numbers for each heater are also listed.
Custom Engineered/Manufactured Heaters
For sizes and ratings not listed, TEMPCO will design and manufacture a
Duct Heater to meet your requirements.
Please Specify the following:
❏ Duct size
❏ Number of circuits
❏ Electrical enclosure
type
❏ Air flow velocity
❏ Element watt density
❏
Over-temperature
❏ Inlet and outlet
❏ Element sheath material
thermocouple, if
temperature
❏ Mounting flange
required
❏ Wattage, voltage and
material
❏
Any
other
phase
❏ Insulation thickness
modifications
Power Control Panels for Process Heaters
Note: Power Control Panels featuring mechanical or
solid state controls with all other necessary components
can be provided by TEMPCO for any size duct heater.
Refer to Section 13, pages 13-56 through 13-63 for complete details.
(800) 323-6859 • Email: sales@tempco.com
11-113