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.
