Mechanical Ventilation

What is It?
Ventilation is the exchange of indoor air for outdoor air. Two types of home ventilation methods include natural and mechanical ventilation. In natural ventilation, outside air enters the house through opened doors and windows. In mechanical ventilation, there are electronic devices such as fans that remove air from a single room, to whole-house systems that remove polluted indoor air and then distribute filtered and conditioned outdoor air throughout the house.

Why Do I Need Mechanical Ventilation?
According to the EPA, sources of indoor pollution that release gases or contaminants into the air are the primary cause of indoor air quality problems in homes. Not providing enough ventilation can aggravate and increase indoor pollutant levels by not bringing in enough fresh, outdoor air to dilute indoor source emissions and also by not carrying enough of potentially unhealthy indoor air pollutants out of the home.

Ventilating a home by opening doors and windows may not always be feasible due to security reasons or outdoor noise levels, rain, snow or weather conditions being too hot or cold to open a window. Mechanical ventilation allows a quiet, energy efficient way to exchange stale and sometimes toxic indoor air for fresh, outside air throughout your entire home.

How Much Indoor/Outdoor Air Exchange Is Necessary?
The air-change needs of houses are not uniform. Not only do they vary from house to house according to the number of occupants, and the presence and strength of various pollutant sources, but, for any given house, they also vary with time as occupants come and go, and pollutant sources wax and wane. Nevertheless, ASHRAE Standard 62, Canadian Standards Association Standard CAN/CSA-F326 and the National Building Code of Canada (NBC) have all established levels of air change that can be expected to meet the peak or near-peak needs of a majority of normal households. (The latter two are based to some extent on ASHRAE Standard 62.)

All three approaches suggest an air change rate of about 0.3 air changes per hour (ach). This is the level of air change used internationally as the norm in terms of analyzing the success of various ventilation schemes. Again, it is recognized that few, if any, houses require constant air change at the rate of 0.3 ach. However, if a house is so tight that leakage fails to provide this level of air change for significant periods of time, it is likely that many such periods of shortfall will coincide with periods when this level of air change is required. When this happens, poor indoor air quality, high humidity, surface moulds and interstitial condensation can result.