Gable Fan CFM Calculator
Powered gable-mounted attic exhaust fan sizing.
Enter your values
ⓘ Live results
Results
- Required fan airflow
- 4,500 CFM
- Rate used
- 3 CFM/sq ft
- Intake NFA needed
- 15 sq ft (at ~300 CFM per sq ft NFA)
- Note
- A powered gable fan can depressurise the attic and pull conditioned air up if soffit intake is inadequate
Quick answer
Powered gable attic fans are commonly sized at 2-3 CFM per square foot of attic floor area, higher in hot climates or dark roofing.
CFM = attic area x rate
How to use the Gable Fan CFM Calculator
- 1Measure the attic floor area.
- 2Choose a rate based on climate and roof colour.
- 3Ensure soffit or other intake vents provide enough net free area so the fan does not pull air from the living space instead.
Worked example
Using the values the calculator loads with:
Inputs
- Attic floor area1500 sq ft
- Climate / roofHot climate or dark roof (3 CFM/sq ft)
Results
- Required fan airflow4,500 CFM
- Rate used3 CFM/sq ft
- Intake NFA needed15 sq ft (at ~300 CFM per sq ft NFA)
- NoteA powered gable fan can depressurise the attic and pull conditioned air up if soffit intake is inadequate
Frequently asked questions
Are powered attic fans still recommended?
Many building scientists now favor sealed, well-insulated attics over powered fans, since fans can worsen air leakage from below if not matched with soffit intake.
Ridge vent vs gable fan?
A continuous ridge vent with soffit intake is passive and often preferred; a gable fan is an active alternative for attics without good ridge venting.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.