For years the building industry has been focused on sealing the holes in our homes to prevent air infiltration. Initially our concerns focused on improving energy efficiency by containing all our conditioned air within the building envelope. Builders at all levels are doing a much better job closing the gaps in walls than we were doing 10 years ago. The question I am asked today centers not on then need to close the gaps, but “How tight is too tight?”
Last fall, I spoke at my local Green Building Council on this very topic and fortunately peaked the interest of our local Habitat for Humanity Director of Construction. He had this very concern over the past two years as their air exchanges dropped below 2.0 Air Changes per Hour (ACH). “How tight is too tight?” he asked. I argued that the best home has 0 ACH with measures in place to mechanically exchange indoor air with fresh air. To understand this, lets explore what is truly measured with a Blower Door Test, the result of which is your ACH rating.
A Blower Door Test measure the amount of air both lost and gained through holes in the home. These holes are in walls, passing through insulation. They are under the interior plate where adhesives, dirt and other contaminate live. Some air is lost around doors and windows. Basically, this is a measure of the amount of unfiltered, untreated air allowed to enter our homes through pathways that add contaminates to the indoor air.
Mechanical ventilation is a means of introducing fresh air into your homes that is filtered and conditioned before entering living space. The cost to seal off unintended pathways is minimal and the cost of mechanical ventilation is reasonable, starting at as little as $250/home. This is a small price to pay for the opportunity to advertise a home that is truly healthier to live-in than their predecessors.
