Whole-House Fans: Do They Work?

Jul 17, 2012 by

Before central air conditioning became common, many houses were built or retrofitted with large, ceiling-mounted fans to blow hot air into the attic. These whole-house fans can have a moderate cooling effect because they create a gentle breeze in certain parts of the house, while also sucking fresh air into the house that might be slightly cooler. Here are the problems with this type of cooling system:

1. Hot air goes out, but “bad” air comes in. A large, whole-house fan creates a great deal of negative pressure inside your house to pull in fresh air, but you don’t have much control over where that air is coming from. In many cases, the cool air is coming from basement and crawl space areas that have dust, dirt, mold spores and bad odors that you don’t want to breathe. In contrast, a central AC system recirculates air from your living space, so you don’t have to worry about breathing air from your basement or crawl space.

2. Humid outside air condenses against cool interior surfaces. When it’s hot and humid outside and the whole-house fan sucks moist air into your house, condensation will take place on cool interior surfaces. You’ll have droplets of moisture collecting here, there and everywhere. Add this moisture day after day and you’ll soon see brown mold stains on drywall, wood and other materials.

3. Air leaks into the attic cause comfort and energy problems in wintertime. As Larry Janesky points out in this video, it’s very important to stop air leakage into the attic during cold winter months. A leaky attic allows the “stack effect” to make your house uncomfortable and expensive to heat, as the interior air you paid to heat leaks up and out of the house. When warm air exits, a similar volume of cold outside air is sucked into the interior through leaks in lower sections of the house. By sealing attic air leaks as Janesky recommends, you short-circuit the stack effect by keeping warm air inside where it belongs. A ceiling-mounted whole-house fan is a huge source of air leaks into the attic; that’s why most home energy experts recommend removing these fans.

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