Determine the volume of air or gas (SCFM) you will be heating.
Determine temperature rise in degrees Fahrenheit (DeltaT in F)
Calculate wattage required as follows:
Watts = (SCFM x DeltaT in F) / 3
Take into consideration the physical size requirements of your application and determine from the specifications chart for each size, the air heater best suited for your application. High watt densities shown in the specifications charts are subject to factory approval due to resistance wire limitations.