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Safe to seal crawl space vents

Hey everyone, I hope this is the best place to ask this. There are several categories I feel this could fit in.

House is setup as this: In central Pennsylvania, split level home with a crawl space under the first floor. Crawl space has a loose stone (2B?) floor, and three metal vents to the outside. The Radon level of the home is rated at the same level as the outside air, but I'm sure it helps that the vents are open. I have never noticed that the stone floor has ever been damp, but I've only really been down there a few times -- But I am fairly certain that the crawl space is dry for the most part.

Last winter I closed the vents, but all that really does is covers the screening with a thin piece of aluminum. Even at this time of year, where the nights are getting down to the lower 40's, I can feel cold are radiating off the first level floor.

My idea, trying to be energy minded and wanting to be comfortable, is to shove foam-board insulation into the vent area during the winter, and open it back up in the spring.

What are your thoughts or concerns? I have heard worries about dampness or radon on an another forum... but I dont know if I should be worried since I dont notice that stuff, and the fact that I would be only doing this from now till Spring.

Looking forward to hearing what you folks think. Thank you in advance.


Re: Safe to seal crawl space vents

That's what I do with my vents. Close them in the winter with foam board and then open them come summer.

Re: Safe to seal crawl space vents

I can only imagine that any moisture there would be frozen anyways during the winter.

I also want to do it because i have kitchen pipes right in front of one of the vents... I mean, they are wrapped in pipe insulations, and havent froze in over 20 years, but still...

Re: Safe to seal crawl space vents

The radon adds a considerable concern.
In general, as someone who's active and aware of the condition of their crawlspace, there's no harm in plugging the vents over the winter - closing them helps but is inadequate by itself.
Just keep an eye on the crawl every month or so, for excess humidity possibly building up.
The radon is an issue - the venting helps keep it under control and you don't want to give it a chance to build. A good poly on the floor, especially if it's caulked to the foundation walls, should provide some barrier - but I can't be sure it will completely eliminate the concern.

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