Energy Saving Ideas

Alternate Ventilation: A Cool Idea for Iowa Homes

After a hot day, nothing is more welcomed than the cool breezes of the night air. In Iowa, instead of using an energy-eating air conditioner in early summer, opening windows and doors can increase air circulation in a home. It’s a free and easy technique called natural ventilation.

Natural ventilation cools a home by maintaining indoor temperatures close to outdoor temperatures while removing heat from the home. Although an air conditioner may be needed during the day, natural ventilation can be highly effective in areas with hot days and cool nights, which makes most Iowa homes eligible for a large portion of the summer. For maximum cooling effect, only ventilate during the coolest parts of the day or night, and then seal off the house from the hot sun and air during the hottest parts of the day. A well-insulated house will gain only 1 degree F per hour if the outside temperature is 85-90 degrees F. By the time the interior heats up, the outside air should be cooler and can be allowed indoors.

The effectiveness of natural ventilation depends on outside factors. The air shouldn't be too humid because the breeze will pull too much moisture in the house. This excess humidity will make the AC unit work harder, removing the moisture before it can begin to cool the home. Natural ventilation is more effective when a home is also surrounded by shade. The shade from trees can cool the air around a home as much as 9 degrees F.

Techniques to capture cool breezes
In climates with daytime breezes, open windows on the breezy side as well as on the opposite side of the house. Keeping interior doors open encourages whole-house ventilation. However, make sure the windows are not directly across from each other. If the cool air has to take a longer path between windows, more of your house will be cooled naturally. Also, a slightly open window will create a better air current than a fully open window.

Attic ventilation
The attic space should also be ventilated since the roof absorbs a tremendous amount of heat in the summer. An improperly insulated and ventilated attic can get as hot as 150 degrees F by absorbing 70-90 percent of the sun's radiant energy, increasing the strain on the air conditioning system. Attic ventilation serves two purposes. It cools hot attics during the summer months and removes moisture from insulation and other building materials during the winter months.

Two key areas should be ventilated. First, vents are needed at or near the top of the roof. Roof, gable, turbine or continuous vents are the best option. Second, soffit vents should be at the lower edge of the roof to allow air to circulate naturally. Attics should have a minimum of one square foot of vent area for every 300 square feet of ceiling area to keep air circulating efficiently.

More Information and Additional Resources
Some of this information was adapted from the American Council on an Energy Efficient Economy's publication, Consumer Guide to Home Energy Savings, 7th Edition, the Energy Efficiency and Renewable Energy Network as well as Homemade Money by Richard Heede and staff of the Rocky Mountain Institute.

Additional information on home energy savings can be found in the Home Series: Home Cooling booklet available on the Iowa Energy Center’s Web site, www.energy.iastate.edu or by calling (515) 294-8819.

The Iowa Energy Center is a nonprofit organization dedicated to increasing Iowa’s energy efficiency and the use of renewable fuels.

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