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Subfloor Ventilation

Subfloor Ventilation

05 May 2018

Ventilation is an important element of an energy-efficient home. Air sealing techniques can reduce air leakage to the point that contaminants with known health effects such as formaldehyde, volatile organic compounds and radon are sealed into the house. Ventilation also helps control moisture, which can lead to mould growth and structural damage. In a tight home, mechanical ventilation is necessary to achieve effective ventilation.

There are three basic ventilation strategies—natural ventilation, spot ventilation, and whole-house ventilation


Natural ventilation is the uncontrolled air movement in and out of the cracks and small holes in a home. In the past, this air leakage usually diluted air pollutants enough to maintain adequate indoor air quality. These days, we are sealing those cracks and holes to make our homes more energy-efficient, and after a home is properly air sealed, ventilation is necessary to maintain a healthy and comfortable indoor environment. Opening windows and doors also provides natural ventilation, but many people keep their homes closed up because they use central heating and cooling systems year-round.

Natural ventilation is unpredictable and uncontrollable—you can’t rely on it to ventilate a house uniformly. Natural ventilation depends on a home’s airtightness, outdoor temperatures, wind and other factors. During mild weather some homes may lack sufficient natural ventilation for pollutant removal. During windy or extreme weather a home that hasn’t been air sealed properly will be drafty, uncomfortable and expensive to heat and cool.


Spot ventilation can improve the effectiveness of natural and whole-house ventilation by removing indoor air pollution and/or moisture at its source. Spot ventilation includes the use of localised exhaust fans, such as those used above kitchen ranges and in bathrooms.


The decision to use whole-house ventilation is typically motivated by concerns that natural ventilation won’t provide adequate air quality, even with source control by spot ventilation. Whole-house ventilation systems provide controlled, uniform ventilation throughout a house. These systems use one or more fans and duct systems to exhaust stale air and/or supply fresh air to the house.

There are four types of systems:

Exhaust ventilation systems Work by depressurising the building and are relatively simple and inexpensive to install.
Supply ventilation systems Work by pressurising the building, and are also relatively simple and inexpensive to install.
Balanced ventilation systems, If properly designed and installed, neither pressurise nor depressurise a house. Rather they introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air.
Energy recovery ventilation systems Provide controlled ventilation while minimising energy loss. They reduce the costs of heating ventilated air in the winter by transferring heat from the warm inside air being exhausted to the fresh (but cold) supply air. In the summer, the inside air cools the warmer supply air to reduce ventilation cooling costs.


Ventilation for cooling is the least expensive and most energy-efficient way to cool buildings. Ventilation works best when combined with techniques to avoid heat build-up in your home. In some climates, natural ventilation is sufficient to keep the house comfortable, although it usually needs to be supplemented with spot ventilation, ceiling fans, window fans, and—in larger homes—whole-house fans.

Ventilation is not an effective cooling strategy in hot, humid climates where temperature swings between day and night are small. In these climates, however, natural ventilation of your attic (often required by building codes) will help to reduce your use of air conditioning, and attic fans may also help keep cooling costs down.

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