Healthy Indoors Magazine

HI October 2017

Healthy Indoors Magazine

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Page 27 of 63

HOUSE CALLS — October 2017 28 What Is the Best Way to Deal with Crawl Space Air? The outside air that you bring into the crawl actually has more moisture in it than the crawl space air you're venting to the outside much of the time. Although the psychromet- ric chart shows mathematically why it doesn't work, a look into just about any vented crawl space in the Southeastern US proves that venting to the outside is often a disaster. The photo above is from a house that was only a year or two old. Although the home builder had installed closed cell spray foam insulation in all the above-grade walls and the attic, he left the crawl space vented to the outside. The result was mold growing on the HVAC system. Let's just say this is your worst option unless you're in a dry climate and quickly move on to the better choices. Conclusion: This is your worst option in humid climates. It's probably also worst for most climates if the HVAC sys- tems and ductwork are located in the crawl space. I f you have a home with a crawl space—or are build- ing or buying one—you have several options on what to do with that particular foundation type. Most crawl spaces are vented to the outdoors, but over the past decade, encapsulating the crawl space (as shown be- low) has gained favor among builders of green and energy efficient homes. It's often seen as the best way to eliminate the moisture problems that often result from vented crawl spaces. But what do you do about the air down there? Before we address that question, however, let me point out that encapsulated crawl spaces are great for humid cli- mates, like the Southeastern US. In a dry climate, it may or not be worth the cost to encapsulate. So, as always, do what's most suitable for your climate. Basically, your options are to do one of the following: • The tried and false method of venting the crawl space to the outdoors • Putting a little bit of supply air from the HVAC system into the crawl space • Using an exhaust fan to move air from the crawl space to outside • Installing a dehumidifier Let's take a look at each of these methods. 1. Vent the crawl space to the outside Do this in a humid climate, and you're asking for trouble.

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