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Whole-house fans draw in cool night air and expel hot air via louvered vents in the attic. Source: U.S. Department of Energy

Whole-house fans draw in cool night air and expel hot air via louvered vents in the attic. Source: U.S. Department of Energy

Snapshot

A whole-house fan can be a comfortable and money-saving alternative to air conditioning. It can even eliminate your need for air conditioning altogether!

Whole-house fans cool your home by pulling in cool air from open windows and exhausting hot air through the attic. They work best in climates with low humidity, and hot days and cool nights.

The illustration below shows how a whole-house fan works. Open all the windows. Turn the fan on. The cool night air is drawn in as the hot air is drawn up into the attic and pushed outside. The fan typically runs for only 20 to 30 minutes at a time. It is sized to cool down your house that fast.

Because a whole-house fan operates by pulling in air from outside, it's not a a good option if you suffer from allergies, are sensitive to pollen, or if you live in an area with significant air pollution.

Installation of a whole-house fan is a job for a professional. A poorly installed whole house fan can be very noisy and will leak winter heat, raising your heating bill.

Savings

The savings from a whole-house fan can be enormous. In the Bay Area, running your air conditioning 6 hours per day costs $150 a month or more. Running a whole-house fan for 1 hour a day-30 minutes in the evening, 30 minutes in the early morning-costs about $3 per month. As much as 95% savings on an air-conditioning bill are typical for a whole-house fan!

Whole-house fans run for just a short period, rapidly sucking up the hot air from the living space on up into the attic, while simultaneously pulling in cool night air into the house from open windows. Every minute a whole-house fan is on, it uses less than 1/10th the energy of a central air conditioner. And, a whole-house fan runs for only a fraction of the time an air conditioner does. The two savings-less energy when used, less time on-really add up.

A whole-house fan requires a vent to the attic, which opens when the fan is on and closes when the fan is switches off. If poorly installed, a whole-house fan will not close properly, allowing leaking home heat in the winter. Ask your contractor about the gasket to prevent air leaks and make sure the fan opening is properly insulated. A good installation saves money in the summer and won't leak out heat in the winter.

How to choose

Tamarack, Airscape, and QuietCool are 3 top-rated brands for whole-house fans available nationwide. QuietCool also has models for flat roofs and for attics with poor access.

The most important choice you can make when planning to install a whole-house fan is getting professional installation. Poorly installed fans leak air in the winter and are noisy when in use.

Your contractor can help you size the fan and create adequate ventilation in the attic. The U.S. Department of Energy recommends 2 to 4 times more than usual attic ventilation when using a whole-house fan, so your contractor may need to expand the openings in your attic to the outside.

To reduce the noise of the fan, consider getting a large-capacity fan and run it at low speed. It will make less noise than a smaller fan running at high speed. And make sure to install a gasket around the edge of the fan where it meets the ceiling; this also will help to dampen the noise.

Finally, buy a fan that is well insulated and seals up tight for winter with an insulated cover for the fan. Otherwise your summer energy savings will be wasted when your winter heat escapes through your attic fan.

Environmental considerations

Whole-house fans are powerful, changing the entire volume of air in your home 30 to 60 times per hour. So if you have allergies or live in an area with poor air quality, think twice before installing one. You will be drawing in a lot of outside air. (Air conditioning with high-quality filters are a better choice when indoor air quality is a concern.)

Because they use just a fraction of the energy of air conditioning (often just 5%), whole-house fans are an environmentally friendly way to cool your house. There are very few home upgrades that have as high impact on your bills as a whole-house fan.


A whole-house fan with an insulated automatic door that opens on a timer.
Photo: Tamarack

File:Whole-house-fan.ogg

Whole-house fan. Photos: WattzOn

Rebates

Utility

Rebate Summary

Getting Started

Alameda Municipal Power

None

City of Palo Alto Utilities

None

Pacific Gas & Electric

$100 rebate

Get started here.

Silicon Valley Power

Up to $200

Get started here.


Take action!

Install a whole-house fan