Ventilation is very important in 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 mold growth, spores, and structural damage. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has determined that a home’s living area should be ventilated at a CFM rate determined by adding 3% of the conditioned space floor area to 7.5 times the number of bedrooms plus one [formula: vent CFM = 0.03A + 7.5 (# bedrooms + 1)] as published by ASHRAE 62.2 in 2013. In a tight home, mechanical ventilation is necessary to achieve this ventilation rate and prevent moisture and condensation from forming inside the walls of the home. ASHRAE Standards are revised every three years.
Four Types of Ventilation Systems
- Exhaust ventilation systems work by depressurizing the building and are relatively simple and inexpensive to install.
- Supply ventilation systems work by pressurizing the building, and are also relatively simple and inexpensive to install.
- Balanced ventilation systems, if properly designed and installed, neither pressurize nor depressurize a house. Rather, they introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air.
- Hear recovery ventilation systems provide controlled ventilation while minimizing 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.
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. Today, 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.
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 localized exhaust fans, such as those used above kitchen ranges and in bathrooms. ASHRAE recommends intermittent or continuous ventilation rates for bathrooms of 50 or 20 cubic feet per minute and kitchens of 100 or 25 cubic feet per minute, respectively.
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.