Is An Attic Fan A Good Investment For My Home?

There is a lot of confusion surrounding attic fans.  Studies have shown if your attic is properly ventilated with a ridge vent and your attic is well insulated, you wouldn’t need an attic fan. A ridge vent is an opening along the ridge of your roof that allows air to enter the lower eves of your attic to naturally take hotter air from the attic up through the ridge vent using natural convection.  

Before providing a simple yes or no answer to this question, you must understand that there are a couple of types of attic fans available on the market. 

Whole-house fans are intended to be used in homes that are not air-conditioned. Whole-house fans are used to bring fresh air into your home, via open windows, and up through your attic.  If you live in the right climate, whole-house fans are a great way to keep your house cool day and night, and only use about 10% to 15% of the power drawn by a central air conditioner.  In the U.S., this type of fan makes more sense in the arid West, rather than in the more humid Eastern part of the country.  

Utilizing this type of fan in our area will introduce potentially humid and unfiltered exterior air into your home.  Many people use their central air conditioning system, not only to cool their home, but also to dehumidify and filter the outdoor air, whereby reducing dust and allergens through a central filtration system.  A whole house fan is the antithesis of your central air system, even if used only at night.  

In most cases, a whole-house fan is mounted in the attic floor, above a rectangular grille in the ceiling of a central hallway.  The fan pulls warm air from the interior of your home and blows it into the attic. Since whole-house fans are relatively powerful, they quickly exhaust the hot indoor air, allowing cooler outdoor air to enter through open windows. Once the house has cooled off, the fan can be turned off and the windows closed. Typically whole house fans are used at night to bring in the cooler air and then windows are closed from early morning until evening, so that the cool air inside the house doesn’t escape.

Even when whole-house fans seem to make sense in your home, they may not be a smart choice due to the following; if your home is located in a neighborhood where open windows may be a security issue; whole-house fans create a big hole in your ceiling which is likely to create a lot of heat loss during the winter, whereby increasing your heating costs; whole house fans are noisy; and lastly, when whole-house fans are used they can cause atmospherically vented appliances located inside your home to back draft, like a gas-fired water heater; whereby potentially creating a carbon monoxide issue. 

A powered attic ventilator (attic fan) has a different purpose: it is designed to lower the temperature of an attic by exhausting hot air from the attic and replacing attic air with outdoor air through roof vents.  The idea is to save energy by reducing the run time of your air conditioner by keeping the attic cooler.  The consideration is that a powered attic ventilator will alleviate some of the heat load on the top floor of your home, whereby providing an energy savings from reduced use of your air conditioning system.

Powered attic ventilators are usually mounted on a sloped roof or the gable wall of an attic. Most powered attic ventilators are controlled by a thermostat so that they turn on when the attic gets hot.  Although the logic behind powered attic ventilators is compelling to many hot-climate homeowners, these devices can cause some problems.  A powered attic ventilator requires make up air to work effectively.  If your roof soffits are not adequate, the attic fan will find other ways to get the air it needs, which can pose a problem.

In many homes, powered attic ventilators pull conditioned air out of the home and into the attic through ceiling cracks. The net result: powered attic ventilators increase rather than decrease cooling costs.  As the cool air is being sucked out of the house through the ceiling, hot exterior air enters the house through other cracks to replace the exhausted air. The net result: the air conditioner has to work harder than ever as it struggles to cool all that entering outdoor air.

Several studies show that using a power attic ventilator does not always save more electric than it uses; even in a newer home with no cracks or air seepage.

A more alarming problem is that powered attic ventilators can also depressurize a house enough to cause gas appliances, like water heaters and boilers used to heat domestic water, to seep hazardous gases into your home. The potential for hazardous conditions is elevated in homes utilizing power exhaust fans during the summer when gas appliances are on at the same time the fan is on.  The negative pressure created by the attic fan causes carbon monoxide to feed back into your home, rather than exhausting up through your chimney.  This can create a potentially hazardous condition for your family.

If your attic is too hot, it isn’t necessarily a problem. If there is no ductwork or HVAC equipment up there, who cares how hot it gets? After all, you should have a thick layer of insulation on your attic floor to isolate your hot attic from your cool house.  If you do have ductwork or HVAC equipment in your attic, make sure you seal any leaking ductwork and make sure your ductwork is wrapped with insulation.

If you believe that your house has a hot ceiling during the summer, the solution is not a powered attic ventilator. The solution is to seal any air leaks in your ceiling and to add more insulation to your attic floor.

Donald Pagano, President – DRP Electrical Contracting

(718) 447-7275   dpagano@drpelectric.com