Attic Fan Size Calculator
Estimate the attic fan CFM and intake vent area needed from square footage, height, and climate adjustment.
CalcSimpler Examples
- 1,200 sq ft, 5 ft height, 15% boost ⇒ 3,450 CFM and 4.60 sq ft intake
- 800 sq ft, 4 ft height, 0% boost ⇒ 1,600 CFM and 2.13 sq ft intake
FAQ
When should I add a climate boost?
Use 10–20% extra airflow for dark roofs, humid climates, or heavy sun exposure.
Does this include soffit vents?
Yes, the intake estimate helps confirm you have enough soffit or gable vents to feed the fan.
What if my attic has multiple sections?
Calculate each section separately or add the areas together if air can flow freely between them.
Additional Information
- Rule of thumb: divide attic volume (sq ft × height) by 2 to size powered ventilators.
- Provide roughly 1 square foot of net free intake vent area per 750 CFM of exhaust capacity.
CalcSimpler