Properly Sizing a Whole House Fan
Finding the right sized whole house fan for your home.
One of the most asked questions we get is, what size whole house fan do I need?
You can size a whole house fan for either a moderate flow, or the breeze effect. Its a matter of personal preference.
Option 1 – Moderate Flow/Efficient Cooling
1.5 – 2.0 CFM Of Air Flow Per SQ FT OF LIVING SPACE
Cooling of your home will take longer with this option. The school of thought behind this is, the greatest benefit from an efficiency standpoint comes within the first few air exchanges in the living area of the home. After that, the cooling effect is diminished. However, a constant flow of air is required to remove the heat that is radiating from your rooms, walls, ceiling and attic.
i.e. A 2000 sq. ft home, would need a 3000 CFM rated fan to achieve the 1.5 CFM Per Sq. Ft. of Living Space. The same home would need a 4000 CFM rated fan to achieve the 2.0 CFM Per Sq. Ft of Living Space.
Option 2 – The Breeze Effect
2.5 – 3.0 CFM Of Air Flow Per SQ FT OF LIVING SPACE
Sizing for this air flow rate is the most popular. People like to feel the “breeze effect” created by a whole house fan. In fact, as the air moves across your body, this moving air has an evaporative affect on your sweat which cools your skin. Sizing a whole house fan at this rate will make you feel coolest, as well as reduce the temperature in your home the fastest.
i.e. a 2000 sq. ft home, would need a 5000 CFM rated fan to achieve the 2.5 CFM Per Sq. Ft. The same home would need a 6000 CFM rated fan to achieve 3.0 CFM Per Sq. Ft.
Here are a few other important factors that you will want to consider when sizing a whole house fan.
1. Do you have high cathedral ceilings?
High ceilings increase the total cubic feet of air space in a home. You will want to take this into consideration when sizing your fan if you have a home with very high ceilings. We recommend sizing up – if you have a home with a lot of high ceilings.
2. Is your home built to a “ranch style” configuration, or oddly shaped?
Also consider sizing up a notch if possible when doing a centrally located system in this style home.
3. Do you have enough existing ventilation to accommodate the airflow off the fan?
Ensure you have enough roof venting to allow the air being pulled into your attic by the whole house fan too escape out, its all about balance. You can read our roof ventilation requirements section for more information.