Seal tight, ventilate right

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Q: Now that winter is here, I’d like to keep cold air out by having a contractor inspect and seal air leaks. However, a neighbor said if I seal up my home too much, it could cause ventilation problems. Is this true?

A: You’re on the right track. Sealing air leaks is usually one of the best energy-efficiency investments a homeowner can make. A typical home leaks, on average, about half of its air every hour, which is like having your kitchen window open all day, every day. Sealing air leaks can also eliminate drafts that keep your home from being cozy.

However, it is possible to seal up some homes so tight they have little ventilation, which can contribute to indoor air-quality problems or a build-up of moisture. The challenge is to achieve the best home performance and energy savings while maintaining air quality. The first step is to eliminate or reduce indoor air pollutants, such as smoke or chemicals.

Experts then recommend sealing air leaks as much as possible. The best way to inspect your home for air leaks is to hire a contractor or energy auditor who will conduct a blower-door test, which uses a powerful fan to measure the air-infiltration rate and locate air leaks. After sealing leaks, the contractor can measure the resulting air-infiltration rate and talk with you about mechanical ventilation, if needed.

Simple mechanical ventilation is controlled and consistent, as opposed to natural ventilation from air leaks, which can result in a home being too drafty in more extreme weather and not ventilated enough in milder weather. There’s no simple way to determine how much mechanical ventilation your home needs—it depends on multiple factors, including the rate of airflow into your home, the climate you live in, the layout and occupancy of your home, and whether there are other indoor air-quality concerns, such as radon or combustion appliances, like gas furnaces.

Mechanical ventilation systems allow for controlled air movement and a dependable rate of ventilation in your home, helping ensure good indoor air quality and appropriate levels of moisture. Generally, newer homes that have been sealed well and manufactured homes have the greatest need for mechanical ventilation.

There are two primary categories of mechanical ventilation—spot ventilation and whole-house ventilation. Spot ventilation systems are the fans above your oven range, in your laundry room or bathroom, and perhaps above a garage workshop. They remove moist air and indoor air pollutants at the source. Generally, these fans work only when you turn them on, but you can install condensation sensors or humidistats, so the fans will turn on whenever they sense a higher moisture content in the air. Keep in mind, running these fans constantly can take too much heated or cooled air out of your home, increasing your energy bills.

Whole-house ventilation circulates air throughout the home and introduces the right amount of outside air. There are four categories of whole-house ventilation systems; determining which is best for you depends on your home’s needs, your budget and your climate.

  • Exhaust ventilation systems: Fans pull air out of your home, increasing infiltration from the outside, either through air leaks or vents.
  • Supply ventilation systems: Fans bring outside air into your home.
  • Balanced ventilation systems: Both supply and exhaust fans circulate air in and out of the home.
  • Energy-recovery ventilation systems: Fans, combined with heat exchangers, modulate the temperature and humidity of incoming air into your home.

Talk with your energy auditor or contractor about whether you need additional mechanical ventilation and, if so, which system would work best for your living space.

Send questions to Energy Q&A, South Carolina Living, 808 Knox Abbott Drive, Cayce, SC 29033, email energyqa@scliving.coop or fax (803) 739-3041.

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Information about finding a home energy auditor is available from the Residential Energy Services Network (RESNET) at resnet.us.