All homes need ventilation – the exchange of indoor air with outdoor air – to reduce indoor moisture, odours 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 odours to linger. Excess moisture generated within the home needs to be removed before humidity levels lead to physical damage to the home or mould growth.

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 (infi ltration) and through vents such as windows and doors – is the traditional method of allowing fresh outdoor air to replace indoor air. Today because of central heating and cooling, as well as the desire for privacy, people tend to make little use of windows for ventilation, so infi ltration 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 air tightness, outdoor temperatures, wind and other factors. During mild weather, such as here in the lower mainland, some homes may lack sufficient ventilation for pollutant removal. Tightly built homes may have insuffi cient ventilation at most times. Homes with high infi ltration rates may experience higher energy costs. Also, infiltration may allow contaminated air to enter from areas such as a garage.

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 and future upcoming code changes will make proper sealing of duct/ventilation systems a way of assuring that fresh air and pollutants are kept separate.

The decision to use whole-house ventilation is typically motivated by concern that natural ventilation is not providing adequate air quality, even with source control by spot ventilation. Whole-house ventilation systems are usually classified as exhaust, supply or balanced systems. The balanced systems for today’s newer tighter homes are using Heat Recovery Ventilation (HRV) systems.

An HRV unit in the design reduces the heating and cooling
costs of ventilation by transferring heat from the warm inside
air being exhausted to the fresh, cold outside air in the winter
and vice-versa in the summer. Comfort is also improved because the supply air is tempered before delivery, reducing
drafts. Some heat-recovery systems also transfer moisture
– an advantage in warm, humid climates in the summer and
cold climates in winter.

Balanced, heat-recovery units are most cost effective in
climates with extreme winters or summers. But as energy
costs increase and with the concern for improved air quality
they will become a standard fi xture in the future.

When installing HRV systems the most effi cient ducts are
smooth, round, short, straight and properly sized. Minimize
the number of elbows. Provide vibration isolation for the
unit. Use mechanical fasteners and duct sealant on all joints
and install proper wall terminations.