Home Series Booklets

A healthy, energy-efficient home needs to breathe

Ventilating Tips | Free Copy | Art Files

Proper ventilation is important to protect your home from moisture damage during the winter and to reduce heat buildup during the summer.

Even if your home is very tight, some moisture will travel to the attic, where it can cause a lot of damage if it's not vented outdoors; you'll see problems such as wet insulation (which is ineffective), water stains on your ceilings and ice dams on the roof during the winter.

Your home needs at least two ventilation sources for circulating air though the attic. Vents high-at or near the top of the roof-and low-at the lower edge of the roof-let air circulate naturally.

At the top of the roof, you can use continuous ridge vents, static roof vents, gable end vents or wind-driven turbines. At the lower edge of the roof, install continuous soffit vents or several single vents in the roof overhang; make sure these vents aren't blocked by attic insulation and allow air to circulate naturally.

Attics with a ceiling vapor retarder should have a minimum of one square foot of vent area for every 300 square feet of ceiling area. If your ceiling doesn't have a vapor retarder, your attic needs twice the amount of vent area, or one square foot for every 150 square feet of ceiling area.

Good natural ventilation makes a power ventilator unnecessary for most homes. However, if you can't get enough air flowing through your attic on its own, a power attic ventilator is an effective, but expensive, solution to solve moisture problems and cool an attic. The best place for a power attic ventilator is near the top of the roof on the side facing away from the prevailing winds. During the winter, a humidistat automatically starts the fan to remove moisture from the attic; during the summer, a thermostat starts the fan when the attic gets too hot.

Here are a few more home-ventilating tips
While keeping the air moving through your attic is the most significant ventilation issue in your home, there are some other things you can do to promote proper ventilation there.

• A basement usually doesn't need to be ventilated, but a crawl space containing water pipes or other utilities does. Install vents that can be opened in the summer and closed tightly in the winter to reduce heat loss. You'll need about one square foot of vent for every 150 square feet of floor in the crawl space. Vents at each corner of the crawl space provide the best air circulation.
• A whole-house fan can be a good substitute for air conditioning, reducing indoor temperatures by several degrees. All you do is open your home's windows during the evenings in warm-weather months and start the fan to draw cool air into your home and expel warm air into your attic and out the attic vents. You can expect lower air-conditioning costs through the prudent use of this energy-saving system.
• Install an exhaust fan in each bathroom to remove moisture from morning showers or steamy baths, as well as putting one in the kitchen to vent moisture and cooking smells. Note that exhaust fans remove heated or cooled air as well as moisture and odors, so use them only when needed. When you go shopping, make sure the fans you buy are properly sized for the rooms in which they're located and their planned usage.

Sidebar

The material in this article was adapted from Home Tightening, Insulation and Ventilation, a book published by the Iowa Energy Center. Besides offering more details on the topics discussed here, this publication describes energy-saving home improvement projects that may be eligible for rebates from local utility companies; low-income assistance and grant programs; special financing opportunities from banks, credit unions and other lending institutions; state incentives; and federal income tax credits.

To get a free copy of this book:

• Call your utility company to see if you can stop by the office and pick up a copy;
• Download a PDF copy at the Iowa Energy Center Web site: http://www.energy.iastate.edu/;
• Request a copy by e-mailing the Iowa Energy Center at iec@energy.iastate.edu; or
• Call the Iowa Energy Center at 515-294-8819 to ask for a copy to be sent to you by mail.

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Contact: Amy Myers, Iowa Energy Center, (515) 294-4391 myers@energy.iastate.edu

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