Home Ventilation

One of the easiest and most effective ways to reduce heating and cooling energy costs is to minimize air leakage or infiltration (see "Air Sealing Measures"). In terms of energy efficiency, the less air leaking into and out of the home, the better. On the other hand, a certain amount of fresh air is necessary for good indoor air quality. If the home is too tight, household products like aerosols and cleaning solutions, cooking fumes and moisture can be trapped inside, causing potential air quality problems. Any combustion-type appliances (furnaces, water heaters, etc.) located within the conditioned space require additional fresh air for safe operation. While saving energy is obviously a good idea, it is important to strike a balance between energy efficiency and indoor air quality.

Indoor Air Quality

First of all, most homes, particularly older ones, have more than enough air leakage to ensure sufficient fresh air. In these homes, basic air-sealing measures should not cause any indoor air quality problems. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) recommends a minimum of .35 air changes per hour or 15 cubic feet of air per minute for each occupant. Most current energy codes are designed to achieve .5 air changes per hour and older homes typically have significantly higher air change rates. However, some new homes, particularly ones built to be very energy efficient or ones with a high number of occupants, may require some additional ventilation to maintain a healthy indoor environment.

Source Control

In many cases, the best way to reduce indoor air pollutants is to eliminate or minimize the source. Avoid using toxic cleaning products, pesticides and solvents (or find non-toxic alternatives). Portable air cleaners can help reduce pollutants in specific rooms or locations in the home.

Spot Ventilation

One way to balance efficiency and indoor air quality is to use some type of controlled ventilation. While infiltration occurs twenty-four hours a day, controlled ventilation can be turned on and off as needed to remove pollutants without unduly increasing energy use and costs. There are certain areas within the average home that typically require more ventilation than others. Spot ventilation can help exhaust contaminants from these areas without increasing the home's overall ventilation rate.

Kitchens can be a major source of cooking fumes, emissions from various household products, and moisture from cooking, dishwashing and other activities. Range hood vents that exhaust these contaminants to the outside can be used intermittently as the need arises. To be effective, the range hood should exhaust to the outside - recirculating hoods filter out grease but do nothing to remove indoor pollutants.

Bathrooms are another area where odors and moisture necessitate higher ventilation rates. All bathrooms, especially those with showers or Jacuzzis, should have a vent fan to exhaust excess moisture outside. After showering or bathing, run the fan for several minutes - at least until the fog clears from the mirror. A timer is one way to exhaust the excess moisture while preventing excessive use.

Laundry rooms are another high-moisture area. All clothes dryers should be vented directly to the outdoors. Any attempt to reclaim the heat from the dryer can result in unacceptably high indoor moisture levels.

In all cases, the vents should terminate outside - not in the attic or other unconditioned area where moisture can condense and cause damage. All vents should have a backdraft damper to minimize the infiltration of outdoor air when the vent is not being used.

Whole-House Ventilation

In extremely tight houses, it is sometimes necessary to provide some additional ventilation for the entire home. There are several ways of doing this. One is to introduce a certain amount of outdoor "make-up" air to the return side of the heating duct system. While this does increase the amount of fresh air in the home, the incoming air must be heated (or cooled) to the desired indoor temperature.

For cold climates where additional outdoor air would increase heating costs significantly, another option is an air-to-air heat exchanger. This device can exhaust stale indoor air while bringing in fresh outdoor air and transfer a large part (60%-80%) of the heat in the outgoing air to the incoming air. This reduces the additional load on the heating system by more than half.

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