Understanding Whole House Ventilation Systems

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All homes need ventilation — the exchange of indoor air with outdoor air—to reduce indoor moisture, odors, and other pollutants. Contaminants such as formaldehyde, volatile organic compounds (VOCs), and radon that may cause health problems can accumulate in poorly ventilated homes. Inadequate ventilation allows unpleasant odors to linger. Excess moisture generated within the home needs to be removed before high humidity levels lead to physical damage to the home or mold growth.

VENTILATION STRATEGIES

To ensure adequate ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) says that the living area of a home should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per minute (cfm) per person, whichever is greater.

Natural ventilation — uncontrolled air movement into a building through cracks and small holes (infiltration) and through vents such as windows and doors—is the traditional method of allowing fresh outdoor air to replace indoor air. Nowadays, because of central heating and cooling, as well as the desire for privacy, people tend to make little use of windows for ventilation, so infiltration has become the principal mode of natural ventilation in homes. Unfortunately, a home’s natural infiltration rate is unpredictable and uncontrollable because it depends on the home’s airtightness, outdoor temperatures, wind, and other factors. During mild weather, some homes may lack sufficient ventilation for pollutant removal. Tightly built homes may have insufficient ventilation at most times. Homes with high infiltration rates may experience high energy costs. Also, infiltration may allow contaminated air to enter from a polluted area such as a garage or crawlspace, or may not ventilate the house uniformly.

Whole-house ventilation — use of one or more fans and duct systems to exhaust stale air and/or supply fresh air to the house—can better control the exchange of indoor air with outdoor air. Energy experts often quote the axiom, “seal tight, ventilate rightâ€