What Is a Whole House Fan?
A whole house fan moves indoor air into the attic and pushes it outside through roof or gable vents. It works best when outside air is cooler than indoor air. Open windows supply fresh air. The fan then pulls heat from rooms, halls, and stairways. Correct sizing matters because weak airflow feels slow, while excessive airflow can create noise or pressure issues.
Why Airflow Size Matters
Fan size is usually estimated with home volume and desired air changes per hour. A higher target clears heat faster. A lower target runs quieter and saves energy. Bedrooms often need gentle airflow. Larger homes, tall ceilings, and warm climates need more capacity. The calculator adds climate and duct loss factors so the result is more realistic than a simple area rule.
Attic Venting Is Important
Every whole house fan needs enough attic exhaust area. If vents are too small, pressure rises in the attic. This can reduce airflow, increase sound, and push dust through gaps. The tool estimates net free vent area in square feet and square inches. Always compare this value with actual vent ratings, not just the visible vent size.
Energy And Cost Planning
Whole house fans often use less power than central cooling during mild evenings. Still, motor watts, nightly run time, and electricity price affect cost. The calculator estimates nightly and monthly energy use. It also estimates heat removal when outdoor air is cooler. This helps compare comfort gains with operating cost.
Practical Installation Notes
Use the result as a planning guide before buying equipment. Choose a fan near the adjusted airflow result. Check that windows can provide enough makeup air. Confirm attic vents are clear. Seal ceiling gaps around the fan frame. Use insulated doors or dampers to limit winter heat loss. For complex roofs, gas appliances, or pressure concerns, ask a qualified installer to review the plan.
Control Tips
Good control settings also matter. Start the fan after the outdoor temperature drops. Open several windows a little, rather than one window fully. This spreads airflow across rooms and reduces drafts. Use a timer for predictable cooling. Recheck vent screens each season, since dust and debris lower the net free area over time steadily.