Recommendation Summary
| Home volume | — |
| Target cooling speed | — |
| Required / recommended fan | — |
| Attic vent NFA needed | — |
| Operating cost | — |
Whole House Fan Sizing Chart
| Home size | Typical fan size |
|---|---|
| 1,000 sq ft | 2,000 – 3,000 CFM |
| 1,500 sq ft | 3,000 – 4,500 CFM |
| 2,000 sq ft | 4,000 – 6,000 CFM |
| 2,500 sq ft | 5,000 – 7,500 CFM |
| 3,000 sq ft | 6,000 – 9,000 CFM |
Based on roughly 15 air changes per hour with 8 to 9 foot ceilings.
Operating Cost & Noise
Estimated draw: — W | Operating cost: — (—). Whole house fans use a fraction of the power of air conditioning. Larger fans move more air but can be louder; look for multi-speed or insulated, ducted models for quieter operation.
What Size Whole House Fan Do I Need?
A whole house fan cools your home by pulling cool outdoor air in through open windows and pushing hot indoor air up into the attic and out the vents. Sizing it comes down to your home volume and how fast you want the air exchanged. This calculator multiplies your living area by ceiling height to get volume, applies a target air-change rate, and returns the required airflow in CFM, a recommended fan size, and the attic vent area the fan needs to actually work. Enter your home size and pick a cooling speed to see the fan to buy.
CFM vs ACH
The two are linked by one formula: required CFM equals home volume times air changes per hour divided by 60. A 2,000 square foot home with 9 foot ceilings holds 18,000 cubic feet, so at 15 air changes per hour you need 18,000 times 15 divided by 60, or 4,500 CFM. Light cooling around 10 air changes per hour is gentle and quiet; aggressive purge at 30 changes clears a hot house fast but needs a much larger fan and more attic venting. Most homes target 15 to 20.
Attic Ventilation Guide
This is where whole house fans succeed or fail. The fan can only move as much air as the attic can exhaust, so it needs roughly one square foot of net free vent area for every 750 CFM of capacity. A 4,500 CFM fan needs about six square feet of net free area; a 6,000 CFM fan needs eight. Net free area is less than the physical opening because screens and louvers block part of it, often cutting it in half, so you typically need about twice the gross vent area. Without enough venting the fan strains, moves far less air than rated, and pressurizes the attic.
Whole House Fan vs Attic Fan
These are often confused but do different jobs. A whole house fan moves large volumes of air through your living space to cool the house and its contents on cool evenings, and you run it with windows open. An attic fan, or powered attic ventilator, only exhausts the attic to lower its temperature and is much smaller. A whole house fan cools you; an attic fan just cools the attic. If your goal is to flush summer heat out of the living space at night, you want a whole house fan.
Climate Suitability
Whole house fans shine in dry climates with big day-to-night temperature swings, where evenings turn cool enough to flush the day heat out and pre-cool the house for morning. They work less well in hot, humid climates where night air stays warm and muggy, since pulling in humid air can add moisture indoors. In mixed climates they are a great shoulder-season tool, cutting air conditioning use in spring and fall. Pair the fan with good attic venting and use it when the outdoor air is cooler than indoors.