What Is Needed to Convert CFM to BTU to Determine HVAC System Size?

Jessie Jean/The Image Bank/Getty Images

The formula for calculating BTU loss or gain in converting CFM to BTU is temperature difference times actual CFM leakage times 1.08 equals BTU loss or gain. CFM is the actual cubic feet of air volume per minute pushed through the HVAC unit. BTU is the British thermal unit of heat removed from the room by the HVAC unit.

To derive the amount of energy needed for the proper heating or air conditioning unit, use the calculation to determine the size of the unit that will not overtax the unit and will sufficiently cool the interior of the property. If the outside temperature is 23, and the inside temperature is 60 degrees Fahrenheit, and the actual leakage is 14,200 CFM, the calculation would be (60-23) x 1.08 = BTU loss or gain or 37 x 14,200 x 1.08 = 567,432 BTU loss or gain per hour. To break down this information further, divide the sum by of cubic feet per minute by 60 to get CFH, as there are 60 minutes in one hour. For this exercise, 567,432 BTU divided by 60 equals 9,457.2 CFH. In this situation, the room is losing 9,457 BTU per hour. To purchase an air conditioner for this room, the air conditioner would need to produce at least 10,000 BTU per hour. A heating unit would need to be rated similarly