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CFM, BTU & Delta T Calculator

Solve any one of BTU/h, CFM, or ΔT in the sensible heat equation — plus total and latent modes. See the factor and the substituted math every time.

Heat type

Q = 1.08 × CFM × ΔT

Solve for

The other two are your knowns.

CFM
°F

Return-to-supply air temperature difference.

Density correction (altitude / temperature)
Correct the factor for real air densityStandard factors assume 0.075 lb/ft³. Turn on for high altitude or hot supply air.
Sensible heat
Sensible capacity
25,920BTU/h
BTU / h
25920
CFM
1200
ΔT
20°F
ƒShow the math
  1. 1.Sensible heatper sensible heat equation
    Q = 1.08 × CFM × ΔT
    1.08 × 1200 × 20
    = 25920 BTU/h

The three heat equations

Air moving across a coil or through a duct carries heat in three ways. Each is the same shape — a constant times airflow times a difference — so knowing any two values gives the third.

  • Sensible: Q = 1.08 × CFM × ΔT. Temperature change only. This is the one you use for furnace rise (40–70 °F) and AC split (16–22 °F).
  • Total: Q = 4.5 × CFM × Δh. Uses the enthalpy difference, so it includes both temperature and moisture.
  • Latent: Q = 0.68 × CFM × Δgrains. The moisture-removal portion, from the change in grains per pound.

Sensible plus latent equals total. If two of them disagree with the third, re-check your temperature and humidity readings before trusting the capacity number.

Frequently asked

What is the sensible heat formula 1.08 × CFM × ΔT?
It is the sensible heat carried by an airflow: Q (BTU/h) = 1.08 × CFM × ΔT (°F). The 1.08 is 60 min/h × 0.075 lb/ft³ standard air density × 0.240 BTU/lb·°F specific heat. So 1,200 CFM across a 20 °F drop moves 1.08 × 1200 × 20 = 25,920 BTU/h of sensible heat.
Where does the 4.5 in the total heat formula come from?
Total heat uses enthalpy: Q = 4.5 × CFM × Δh, where Δh is the enthalpy difference in BTU per pound of dry air. The 4.5 is 60 min/h × 0.075 lb/ft³. Total heat captures both temperature and moisture change, so it is the fullest measure of coil capacity.
What is the 0.68 latent heat factor?
Latent heat from moisture removal is Q = 0.68 × CFM × Δgrains, where Δgrains is the change in grains of moisture per pound of dry air. The 0.68 is 60 × 0.075 × 1,061 ÷ 7,000, folding in the latent heat of water and the 7,000 grains per pound. 1,200 CFM removing 30 grains is 0.68 × 1200 × 30 = 24,480 BTU/h latent.
Do I need to correct 1.08 for altitude?
Yes if you are well above sea level or the air is hot. The factors assume 0.075 lb/ft³ standard air; thinner or hotter air carries less heat per CFM. Turn on density correction and enter your altitude and coil-air temperature — at 5,000 ft the 1.08 drops toward roughly 0.9.
How do I get Δh and Δgrains for total and latent modes?
From the entering and leaving air conditions. Read each side's dry-bulb and wet-bulb, look up enthalpy and grains for both in the psychrometric calculator, and subtract. This calculator then multiplies by the airflow to give total or latent BTU/h.

Related tools

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CFM per Ton Calculator

Check that the airflow you plugged in matches the tonnage.

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Psychrometric Calculator

Get the enthalpy and grains for total and latent modes.

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Target ΔT Calculator

Is your ΔT what it should be for these conditions?

Sources & references

Estimates for planning purposes only. Verify all results against the code edition adopted in your jurisdiction and with your Authority Having Jurisdiction (AHJ). This tool is not a substitute for a licensed HVAC contractor. See our methodology, sources, and code editions.