calcs.homes
calcs.homes
Enter your home's square footage and ceiling height to size an attic-vented whole house fan — a much bigger airflow job than a single room's exhaust fan.
Estimate only — also confirm your attic has enough vent area to exhaust that airflow.
CFM = house volume × target air changes per hour ÷ 60. Whole house fans pull outside air through open windows and push warm indoor air into the attic, typically targeting 2-3 complete air changes per hour for effective evening cooling. Unlike a bathroom fan, this is a whole-building airflow calculation — look for a fan rated at or above the recommended CFM.
2-3 ACH is the standard target — enough to fully replace the home's air every 20-30 minutes, which is effective for cooling in the evening once outdoor temperatures drop.
Yes — insufficient attic ventilation can cause backdrafting or reduced airflow. As a rule of thumb, aim for at least 1 sq ft of net free vent area per 750 CFM of fan capacity.