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EPA Energy Star

Balanced Ventilation Systems

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The following came from the EPA’s Energy Star web site: 

The air within homes can become stale from moisture, odors, and pollutants that penetrate the home or are generated internally by human activity and out gassing from building materials and furnishings.  A constant supply of fresh, outdoor air can provide greater assurance of good indoor air quality and improved comfort. 

In most homes, ventilation is provided accidentally when air leaks through the building envelope.  Accidental ventilation is unreliable because it is dependent on a pressure difference between indoor and outdoor spaces caused by temperature or wind variations.  Too much fresh air often enters a house during cold weather, causing uncomfortable drafts and high heating bills.  Not enough fresh air may enter during mild weather which can lead to poor indoor air quality. 

Air leakage through the building envelope accounts for between 25 percent and 40 percent of the energy used for heating and cooling in a typical residence.  Many new homes are being air sealed to reduce this energy use.  Where tighter construction reduces air leakage and accidental ventilation, active ventilation systems may be needed to provide fresh air. 

Figure 1 shows how a balanced ventilation system works in a small home.  Fresh air enters the home through a single intake and is then distributed through ducts to the living and sleeping areas.  Stale air is removed from the home through a separate exhaust duct with inlets typically located in the bathrooms.  The kitchen has a separate, manually operated exhaust fan located in the range hood.  These systems can operate continuously or only when home are occupied.  The supply and exhaust fans are equal in capacity to maintain indoor pressure balance. 

In severe climates, balanced ventilation systems can be equipped with a heat exchanger that recovers most of the heating and cooling energy from the exhaust air.  There are two types of heat exchangers: sensible and total.  Sensible heat exchangers recover dry heat.  They are well suited for cold climates and are becoming common in many parts of Canada and the northern United States. 

Total heat exchangers transfer heat and moisture for additional humidity control.  They work well in both cold and moderately humid climates, and can help prevent moisture-related problems.  Balanced ventilation systems can be used safely with all types of heating and cooling equipment, but are more expensive than other ventilation systems (exhaust and supply ventilation). 

Resources for this article:

    1. The Consumer Guide to Home Energy Savings (Wilson and Morrill), available from the American Council for an Energy Efficient Economy at 510-549-9914
    2. Moisture Control in Homes fact sheet available from the Energy Efficiency and Renewable Energy Clearinghouse (EREC), POBox 3048, Merrifield, VA 22116, (1-800-363-3732)

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