How do Whole House Fans Work?

A Whole House Fan is installed in the ceiling of your home and sucks up the air inside (like a vacuum cleaner) and blows it into the attic. This creates a negative pressure inside the living area and draws cooler outside air through open windows or doors. You can literally feel a draft as the air moves in your home (lower chill temperature).

Whole House Fan Air Flow

Whole House Fan – Air Flow Schematic

This air exchange only really makes sense whenever the outside is cooler than the inside of your home. So during hot days the Whole House Fan usually is turned on in the evening reducing the need to run the A/C into the night. During transition periods (like late spring or early fall) Whole House can completely eliminate the need to run the A/C at all as the chill factor of the air draft is sufficient to cool the home.

Unlike Air Conditioning, where the existing air is cooled by extracting heat (which require a lot of electricity), the dramatically more energy-efficient Whole House Fan replaces the hot air in its entirety with cooler outside air. In addition a Whole House Fan cools the house itself and not just the air inside.  In contrast an A/C doesn’t cool the actual building just merely the air inside. That is the main reason why A/C’s tend to cycle on and off throughout the night re-cooling the ambient air while the hot thermal mass of the house radiate more heat back into the home.

The are several benefits to a Whole House Fan:

  1. It is extremely cost effective. Running a Whole House Fan draws a fraction of electricity compared to an A/C unit (for my setup: $0.07/hour (WHF) vs $0.81/hour (A/C)
  2. It is healthy as a Whole House Fan replaces used-up indoor air with fresh outdoor air. An A/C is a “closed loop system” which means it recirculates the same ambient air over and over. Indoor pollution and odors builds up within a home that is not properly vented.
  3. A Whole House Fan speeds up the process of cooling down you attic after a hot day. During the summer attics can get heat up to 130 degrees Fahrenheit. It can take 4-5 hours deep into the night for that heat to leave the attic through vents and whirly birds. A Whole House Fan that runs in the evening for just 30 min. completely cools the attic to match the outside temperature.
  4. Modern WHF are whisper quiet: You practically have no sound pollution inside and outside your home. You can probably tell when your neighbor is running his A/C but you would never know if he has a WHF in operation.

Where does a Whole House Fan work best?

In general the less humid the climate the better it is for operating a Whole House Fan.

We live in Los Angles and it has the perfect weather for using this efficient cooling system. The days are hot and dry, but the nights tend to cool down quickly. So for most of the summer we can actually switch over from our A/C to the Whole House Fan by the time the sun sets. This is usually the peak time for running an A/C as the house is at its hottest, having absorbed all that afternoon heat by the attic and walls of the building (thermal mass).

We also estimate that because of our WHF we do not need to run our A/C for an additional 2 month a year.

Before Installing a Whole House Fan:

  • Venting: It is important that you have enough opining in your attic for the air to escape. There need to be enough whirly birds, vent holes or dormer vents inside the attic in order to avoid building up pressure in your attic that could force the air back into your home through cracks in the ceiling or your wall structure.
  • Building Codes: Check with your city about the venting requirements of your home. They differ by the age of your home. There may be permit requirements (it wasn’t the case for my city but you never know)
  • Rebates: Also check with your local city, they very likely have an incentive program where they will rebate you a  portion of the cost for buying and installing a WHF. My city paid me $100 per fan, so $300 total.
  • Installation: Be realistic about your “handy man skills”: Installing an WHF requires standing on a ladder, cutting a whole into your ceiling and doing some basic electrical work. There is nothing complicated about the installation but do hire an electrician if you do not have the experience. (Some models do not require wiring as they come with a power plug and a remote controlled switch).
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