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Calculation Machine

Garage Ventilation CFM Calculator

Exhaust fan size for a garage or workshop.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Exhaust fan size
500 CFM
Air changes used
6 ACH
Garage volume
4,752 cu ft
Intake opening needed
137 sq in

Quick answer

Garages usually need 6–12 air changes per hour, rising to 20 or more where engines run or solvents are used.

The formula

CFM = garage volume x ACH / 60

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Garage length24 ft
  • Garage width22 ft
  • Ceiling height9 ft
  • Main useParking and storage

Result

  • Exhaust fan size500 CFM
  • Air changes used6 ACH
  • Garage volume4,752 cu ft
  • Intake opening needed137 sq in

How to use the Garage Ventilation CFM Calculator

  1. 1Measure the garage and enter the dimensions.
  2. 2Pick the use case — running engines demand far more air.
  3. 3Fit the exhaust high and the intake low on the opposite wall.

Frequently asked questions

Is a window enough?

Not when engines run. Carbon monoxide needs mechanical extraction with make-up air.

Where should the fan go?

High on the wall furthest from the intake so air sweeps across the whole space.

About this calculator