Ventilation is the process of removing polluted, stale, moisture-laden indoor air in the home and replacing it with fresh outdoor (often drier) air. Over the past several decades there has been a trend in the residential building industry to make houses more energy-efficient during construction, which means homes are sealed tighter than in the past. Having proper ventilation is essential for the well-being of the home’s occupants.
How much ventilation is actually necessary?
There are different theories regarding how much ventilation is “ideal” for a home. In residential construction, an ideal amount of ventilation has generally been accepted to be on the order of 0.3 air changes per hour. In other words, the indoor air is completely replaced with outdoor air approximately once every three hours.
What is natural ventilation and how is it measured?
When blower door tests are completed on new houses with extremely well-sealed thermal envelopes and a result of less than 0.2 air changes per hour is calculated, balanced ventilation equipment is often recommended for installation. These systems draw in fresh air from the exterior and discharge stale air from the interior in equal amounts.
In spite of all of the efforts to make the building envelope more airtight, some air still leaks through the building’s thermal envelope. This leakage is called natural ventilation.
There are several key factors that affect natural ventilation, including how well a building’s thermal envelope was sealed during construction, stack effect (a pressure effect caused by temperature differences between the outside and inside of the house, which is most pronounced in the winter) and wind.
The amount of natural ventilation that occurs is completely specific to each house and is commonly measured by completing a blower door test on a home.