CFM to BTU Calculator (Airflow and Heating Load)
Use Q = 1.08 × CFM × ΔT to solve for whichever of airflow, sensible capacity or temperature difference you do not know. Handy for checking a furnace temperature rise, a coil delta T or the CFM a space needs.
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The formula
Q (BTU/hr) = 1.08 × CFM × ΔT. The 1.08 comes from air density (0.075 lb/ft³ at standard conditions) times its specific heat (0.24 BTU/lb°F) times 60 minutes. It is valid for sensible heat at sea level; at altitude, multiply by the density ratio.
As a rule of thumb, cooling systems move about 400 CFM per ton (350 for humid climates, 450 for dry). A 12,000 BTU/hr ton at 20°F delta T needs 12,000 ÷ (1.08 × 20) = 556 CFM of sensible-only airflow, which is why total capacity (sensible plus latent) matters.
Worked example
1,200 CFM through a coil with a 20°F temperature drop moves 1.08 × 1,200 × 20 = 25,920 BTU/hr of sensible heat.
Frequently asked questions
Does this include latent heat?
No. It is the sensible heat only. Total capacity also includes the moisture removed (latent), which this formula does not cover.
What temperature rise should a furnace have?
Check the nameplate: gas furnaces are typically rated for a 30 to 60°F rise. Measure supply minus return temperature and compare.
Does altitude matter?
Yes. Thinner air carries less heat, so the 1.08 factor drops. At 5,000 feet it is about 0.90.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.