GENERAL
7.Installation in duct larger than heater. For installation where the duct dimensions exceed the insert type heater dimensions, the area beyond the heater dimensions must be filled with wire mesh, expanded or perforated sheet metal of 50% open area as shown in Figure 11. This will maintain a uniform air velocity across the face of the duct.
Inner Baffle | Insert Type | Perforated Metal |
| Duct Heater | (50% Open Area) |
Remove Bracket and |
| Oversized Duct |
Use Sheetmetal Screws |
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Thru Same Holes into Duct. |
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Figure 11
8.Installation with flexible duct. Where a duct heater must be installed near a flexible duct connection, be certain that a 4’ minimum distance between the duct heater and the flexible connector exists and that the connector is suitable for 195°F temperature. (Refer to Figure 12).
9.Do not install duct heater outdoors. Duct heaters cannot be installed with rooftop equipment where they are exposed to the weather.
Flexible Duct
(Must be suitable
for 195°F)
Air
Flow
Duct Heater
4 Ft.
Min.
Figure 12
10.Installation with dampers or filters. Maintain at least 4’ dis- tance between duct heater and damper, filter frames, or other similar obstructions. (Refer to Figure 13).
| 4 Ft. |
|
| Min. |
|
Damper | Duct | Air Flow |
| ||
Heater |
| |
| Top of Duct | |
|
| |
| Figure 13 |
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Clearance: Zero clearance between duct heater and combustible materials such as wood is permissible. However, adequate clear- ance must be provided around terminal box for proper ventilation and future service accessibility.
AIR FLOW
Flow through duct heater must never drop below the minimum air velocity shown on duct heater nameplate. If the air handling system includes filters, they must be cleaned whenever necessary in order to maintain air flow above the minimum, otherwise poor temperature control and discomfort will result.
If air flow is poorly distributed within the duct, deflector vanes must be added to provide correction.
The minimum air velocities shown on the nameplate are not to be considered average readings. Do not add various velocities taken across the face of the duct, find an average value, and com- pare it to the minimum velocity shown on the heater nameplate.
The minimum air velocity refers to any point along the face of the duct heater when checking duct velocities, no velocity can be below that sown on the heater nameplate (remembering inlet air temperature). Velocities are best checked with an anemometer, tak- ing numerous readings along the horizontal and vertical centerline of the duct heater at the location prior to installation or slightly up stream from the heater after installation. (Refer to Figure 14). Large ducts will require additional readings taken at locations in addition to the centerline.
Duct Heater
Air | Flow | |
Velocity | ||
| ||
| Profile |
Figure 14
Incoming Air Temperature: Incoming air temperature entering the duct heater must not exceed 100°F.
Example: 500 FT./MIN. Minimum Air Velocity on Heater Nameplate.
| 600 |
|
|
| 200x | |
| 500 |
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| 400x | |
| 700 |
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| 800 |
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Velocity | 600 | Velocity |
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| 900 |
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Profile | 900 | Profile |
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| 600 |
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FT./MIN. | 700 | FT./MIN. |
|
| 700 |
|
| 600 |
|
|
| 200x | |
| 500 |
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|
| 300x | |
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|
|
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| 400x | |
RIGHT: |
| WRONG: |
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500 FT./MIN. MINIMUM | 9 |
| 4500 = 500 FT./MIN. AVERAGE | |||
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| X – below 500 FT./MIN. |
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