Thermolec Application &Technical Notes - Manual (Page 51)

4-KILOWATTS PER SQUARE FOOT
Since tubular elements surface temperature lag behind the resistance wire temperature due to mass and insulation, and
in order not to exceed the maximum temperatures allowed by UL, a tubular duct heater is not permitted to have the same
concentration of wattage as an open coil heater. Thermolec open coil duct heaters have listing of 22.5 KW per square
foot. For tubular duct heaters, the limitation is usually about 13KW per square foot.
5-PRESSURE DROP
Open coil heaters cause a smaller static pressure drop than do tubular heaters. This may permit the use of a smaller
blower with resultant energy savings. A typical tubular heater with 600 feet/minute face velocity has .60 inches of water
pressure drop, while the same size open coil heater with the same face velocity has only .03 inches of water pressure
drop.
APPLICATION NOTES
THERMOLEC