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Calculation Machine

BTU to CFM Calculator

Airflow from heating or cooling load.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Required airflow
1,667 CFM
Equivalent tons
3
At 400 CFM/ton
1,200 CFM
In m³/h
2,832

Working

  1. 136,000 / (1.08 x 20) = 1,667 CFM

Quick answer

For air, sensible BTU/h equals 1.08 times CFM times the temperature difference, so CFM = BTU/h / (1.08 x ΔT).

The formula

CFM = BTU/h / (1.08 x ΔT)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Sensible load36000 BTU/h
  • Temperature difference20 °F

Result

  • Required airflow1,667 CFM
  • Equivalent tons3
  • At 400 CFM/ton1,200 CFM
  • In m³/h2,832

How to use the BTU to CFM Calculator

  1. 1Enter the sensible load in BTU per hour (not total load with latent heat).
  2. 2Enter the design temperature split — 20 °F cooling, 40–70 °F for furnaces.
  3. 3Use the airflow to size ducts and blower speed.

Frequently asked questions

Where does 1.08 come from?

It bundles air density, specific heat and the 60 minutes per hour into one constant at standard conditions.

Do I use total or sensible BTU?

Sensible only — latent load removes moisture and does not change air temperature.

About this calculator