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We just completed a 20x20 great room addition on the side of our house with a 4 foot crawl space and poured concrete floor. There is a 4’ by 4’ cut through to access this crawl space from the existing full sized basement. We live in New England. The new addition has baseboard heat and the floor is insulated with insulation bats. The new addition includes 3 foundation vents (metal with screens, we can slide them open or closed) for the crawl space. The rest of the existing basement has no venting to the outside (just a door with stairs to a bulkhead).

The contractor said these are required and wants them left open. However, in the winter - even if we slide the vent closed, cold air is making the floors cold and it just lets cold air into the normal existing basement which will be half finished.

Do we need these vents or can I just plug them with some sort of ridid foam insulation? All this cold air seams like a big waste of energy. In the summer we keep a dehumidifier running - is this enough to keep the crawl space conditioned as well?

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    Hello, and welcome to Stack Exchange. Is there a reason why you wouldn't close off and insulate that 4' x 4' cut-through from your full-sized basement to the new crawl space? Nov 18, 2018 at 17:58
  • I am open to closing this off if recommended. My thought was that if we seal the crawlspace vents, then warmer air from the basement could pass into this crawlspace to help keep it warmer (reducing risk of heating pipes freezing, keeping the living space above it warmer)
    – Andrew
    Nov 18, 2018 at 19:12
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    Wait: your extension is electric, not forced water, right? If so, then what's going to freeze in the crawlspace? Nov 18, 2018 at 20:07
  • No - it is baseboard heat (non-electric). the feed for those baseboard units is under the floor.
    – Andrew
    Nov 19, 2018 at 15:56
  • So, letting the crawlspace freeze wouldn't be a problem, right? Nov 19, 2018 at 15:58

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