We all know about how stack effect works in homes, but during presentations, I’m always surprised by how many hands are raised in response to the question: “How many of you think you can make a house too tight and cause problems with indoor air quality?” Generally, at least three-quarters of the room raises their hands. Really? My colleague Joe Kuonen says that getting a house so tight that you need to ventilate is a feat worth celebrating. “Now, we can get fresh air from a place we can trust,” he says. Where do most of our homes get their fresh air? From places we cannot trust, like crawl spaces.
What do we know about crawl spaces? Generally, they are dark and wet. This is a perfect habitat for mold, rodents and insects to thrive – and gain access to the house. Those of you who have spent a lot of time in crawl spaces have horror stories about close encounters with both living and dead creatures. Allison Bailes once published a photo of a dead opossum in a crawl space next to a disconnected return duct!
On the other side of the band joist is the basement where the air handling unit often resides. If there is insulation on the band joist, it is generally discolored by filtering air that passes through the crawl space. Thankfully there is a furnace filter, you might say. If you look at most furnace filters in people’s homes, you’ll generally find them clogged and gross. And with the furnace filter slot at the end of the return duct, the furnace filter is protecting the blower motor from the air that everyone in the house has been breathing. This can’t be good for your health.
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