Thermolec Application &Technical Notes - Manual (Page 14)

THREE EASY STEPS
STEP 2 - (continued)
Airflow Uniformity
In order to prevent hot spots, the air flow must be uniformly distributed across the heater area.
The following figures illustrate typical heater mis-application where the airflow is not uniform.
An NEC article (please see below *) specifies that a heater should not be installed closer than 4 feet
downstream or 2 feet upstream from a fan outlet, an abrupt transition, an elbow or any other kind of
obstruction in the duct. If your application is such that one of the mentioned installations cannot be
avoided, THERMOLEC can help you by designing around it.
* 1071 NEC Article 424-59:
"Means shall be provided to assure uniform and adequate airflow over the face of the heater. Heaters installed
near (within 4 feet) a fan outlet, elbows, baffle plates or other obstruction in duct work may require turning
vanes, pressure plates or other devices in the inlet side of the duct heater to assure an even distribution of air
over the face of the heater".
Filter Frame
Heater too close to fan
Heater too close to filter
Heater too close to elbow
Heater too close to transition
Overheating
Conditions