Sensible Heat Calculator (1.08 × CFM × ΔT)

Sensible heat changes air temperature without changing its moisture. It is the most-used airflow/capacity relationship in the field.

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Formula

Q (BTU/h) = 1.08 × CFM × ΔT (°F)

Variables

1.08: — 0.075 lb/ft³ × 0.24 BTU/lb·°F × 60 min/h (standard air)
ΔT: — Supply–return temperature difference

Example calculation

1,200 CFM × 20 °F ΔT × 1.08 = 25,920 BTU/h (7.6 kW).

Practical HVAC use

Estimate delivered heating or sensible cooling capacity, or back-calculate airflow from capacity and ΔT.

Common mistakes

Using the formula at high altitude without a density correction.
Using total cooling capacity — only the sensible portion applies.

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Calculate latent (moisture) heat load from airflow and humidity ratio difference in grains per pound: Q = 0.68 × CFM × Δgr.

Total Heat

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Calculate total (sensible + latent) heat from airflow and enthalpy difference: Q = 4.5 × CFM × Δh. Includes tons and kW.

Temperature Rise

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Calculate furnace temperature rise from supply and return temperatures and estimate airflow from output.

CFM per Ton

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Calculate airflow per ton of cooling and L/s per kW.

Educational tool. Results are estimates from the stated formulas; always confirm with manufacturer data and the code adopted in your jurisdiction. All calculators