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I've asked this question before:

What are the pros and cons of a vented vs unvented crawl space?

However, now that I'm going to get air conditioning the question comes back again and again people seem to have different opinions.

I'm the DC area where the summers are hot and humid.

I've got 2" rigid foam insulation on the perimeter walls of my crawl space and an interior perimeter drain system covered with gravel. I'm going to cover the dirt with 2 layers of 6 mil plastic.

Now, I've got a few bids for AC and the AC guys have different opinions on the question of conditioning the crawl space. The guy that I may end up going with thinks that I should vent the crawl space in the summer and isolate it from the basement (my space underneath is divided: 1/2 crawlspace 1/2 basement).

However, there's this article:

http://www.buildingscience.com/documents/reports/rr-0401-conditioned-crawl-space-construction-performance-and-codes/?topic=/doctypes/researchreport

that talks against the idea. My bidders think it's OK to condition it (small register + return at the opposite end).

FWIW, I may also add a radon exhaust fan hooked into my french drain.

Given all the above info and your experience, what decision would you make if you were in my shoes?

Community
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Peter Q
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3 Answers3

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I don't live in a hot climate, but I do know one thing, heat rises and cold falls. i can't understand the justification of putting AC into a crawl space that is not air tight. I answered your question a long time ago about insulating and venting the crawl, and I still stand by that advise. I can not believe the air conditioning a dirt floor crawl space is going to positively effect the temp in the house above by any measurable amount. I think it will a waste of energy and money to AC the crawl. I COULD BE WRONG, but I'd love to hear a compelling argument for doing it.

shirlock homes
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If you are putting air handler or ducts in the crawlspace, you should seal and condition it. This will save more energy than the additional energy used to condition the extra volume of space. It will also result in better comfort (ducts will do a better job of delivering conditioned air) and protection from moisture than having them in a vented crawlspace.

You already have insulation at the crawlspace walls. If you add vents, it defeats the purpose of that insulation. It is much more difficult to insulate the crawlspace ceiling successfully.

littleturtle
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See http://www.advancedenergy.org/portal/crawl_spaces/pdfs/ASHRAE%20IAQ%20Paper%20Revised%202008-07-15.pdf

And http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

And especially: http://aceee.org/files/proceedings/2004/data/papers/SS04_Panel1_Paper07.pdf (Moisture Solution Becomes Efficiency Bonanza in Southeastern United States Bruce Davis and Cyrus Dastur,, U.S. Department of Energy, National Energy Technology Laboratory #DE-FC26- 00NT40995)

Bryce
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