Whole-House Fans and Attic Ventilators

House Doctor | Gary Dymski

August 10, 2000

YOU'VE PROBABLY made the mistake of using your oven to cook on a hot day. Remember standing near the oven and that suffocating heat? Think of your attic as that oven.

Hot air trapped in an attic has nowhere to go but back into the home's living area. When it's 95 degrees outside, the air temperature up there can reach 135 degrees or higher. This attic air radiates heat back into the home, making not only for uncomfortable living-even after the sun goes down- but also increasing chances for structural damage to your roof. During summer, hot attic air can shorten the life of asphalt shingles and cause wood buckling. Because of the humid conditions on Long Island, moist air trapped in attics, especially during winter months, can cause wood rot.

One solution, especially with older homes, is installing whole-house fans or attic ventilators. These can replace the hot, stagnant air in your attic to create a cooler living area and extend the lifespan of your roof.

Whole-house fans are those box-type assemblies that typically fit into a hallway ceiling on the second level of your home. Attic ventilators are power fans covered with a button-shaped hood and are installed on the roof.

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Each type of device does a good job of exchanging attic air, but you should determine your needs before deciding on which to install. If you want to cool your house in the summer, your best bet is probably a whole-house fan. For continual ventilation, even during winter, an attic ventilator is the better choice. Both can be installed by an accomplished do-it-yourselfer, and manufacturers provide excellent installation instructions. However, experience in electrical wiring and the ability to mount some roof vents and cut into your roof probably will be required.

Whole-House Fans. These fans have come a long way since they were introduced in the 1950s. They're quieter, more durable and easier to install now. Most mount in a ceiling on a top floor and cost less than $ 200. There are two types: direct drive, in which the motor is attached to the fan, and belt drive, in which the motor is mounted above the fan. Belt-drive fans are typically quieter and a bit more expensive.

Installation typically involves cutting away a piece of the drywall ceiling and fitting the fan between joists or straddling it atop joists. To fit some bigger fans, joists might have to be cut. Before you cut any joists, however, check with an engineer or a contractor. Cutting into joists might damage the structural integrity of your house.

It's also good idea to wire the fan to its own circuit on the service panel. However, fans can use existing circuits-if they don't overload them- and be controlled by switches and timers.

The biggest advantage to a whole-house fan is the ability to pull in cool, fresh air. You can slash central air-conditioning bills by running the fan in the morning to cool the house before the air conditioning is turned on. At night, the air conditioning can be turned off, and the house can be cooled by the fan.

Of course, the fan can only operate when windows in the house are open. Air is drawn into the house through the windows and pushed out through the attic. It escapes the attic through roof vents.

These fans are seasonal, of course,and do not do a good job of cooling on hot, muggy days when outdoor temperatures are 82 degrees or higher.

Attic Ventilators. These devices (starting at about $ 50) suck fresh air into the attic through intake vents installed under eaves and on sides of the attic. Old air escapes through roof vents. Ventilators perform best when wired to a combination thermostat/humidistat. When attic temperature and humidity reach a certain point, the ventilator automatically goes on.

There's some controversy about using attic ventilators in conjunction with central air conditioning. Some heating and cooling experts believe that when both run simultaneously, cool air from the house escapes into the attic. Other experts feel lining attics with a vapor barrier-usually a layer of plastic on the attic floor-and extra insulation keeps cool air from escaping into the attic.

If you have central air and want to install either a whole-house fan or attic ventilator, consult with a heating and cooling contractor first. Also, fans and ventilators are designed to move specific amounts of air-measured in cubic feet per minute.

You'll need to size your attic before picking a fan or ventilator, and adding roof vents-intake and exhaust-might be required. It sounds more difficult than it is. Do some research first by visiting an electrical supplier and reading literature on the box of a fan or ventilator. Most manufacturers print required fan size and number of vents for a specific attic size right on the box.