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Crawl space air transfer

LItoadk | Posted in General Questions on

Hi I have an unvented crawlspace in zip code 12808. Electric baseboard . I want to trade warm air from the conditioned space to crawl space, what is the the proper way to do this

thanks in advance for your expertise

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  1. silkwj | | #1

    NYS code (IRC) Chapter 4 Section R408.3 says you need 1 cfm per 50 sf of crawlspace area (See, either exhaust or transfer to & from the conditioned space. Hopefully the crawlspace has a vapor barrier and is insulated...? Any existing moisture problems? Is this a new build or existing condition you're changing to solve a certain problem? Could be a couple interconnected issues if you're trying to fix something - moisture problem, air quality, cold floor...?

  2. LItoadk | | #2

    The crawl space is insulated at the perimeter walls and there is a vapor barrier on the floor. No moisture but the crawl gets cold in the winter and I want to keep the water on all winter so I want to Heat the living space and transfer heat to the crawl space making it a conditioned space. Can you suggest a detail or product to equalize the temp between crawl and living space

  3. ohioandy | | #3

    A typical way to get conditioned air into a crawlspace is to open a hot air register in the space. In many cases there are ducts already down there, so it can be an easy modification. You said your heat is electric baseboard, so that's a little tougher. Warm air is bouyant; it's an energy-intensive thing to push warm air down. It would take a combination of a big fan and registers. You said your crawlspace is insulated... is it WELL insulated? And air-sealed? Conditioning a leaky crawlspace is even MORE energy-intensive (i.e. expensive and wasteful.) If your only goal is to prevent a waterline from freezing, you'd probably be way ahead to use a heating tape around the exposed pipe.

    By the way, have you read the following article on this site? Gives good background on why and what:

  4. Expert Member


    The two ways our code suggests are:

    - Provide a certain percentage of openings based on the square footage of the crawlspace between it and the floor above.
    - Provide an exhaust fan to the exterior and a make up air grill to the floor above.

    These are recent options that came in when full time mechanical ventilation was required for houses. Before that the most common response was just to add an additional baseboard heater in the crawlspace.

  5. LItoadk | | #5

    We are amateurs but we air sealed and insulation is 1” eps( before I was aware of the benefits of poly iso) with a cement skim coat on the outside
    I think I need some sort of eclectic fan unit in a floor register
    I was thinking of one fan in one corner of the rectangular floor plan and then another in the opposite corner acting as a supply and a return to circulate warm air thru the crawl
    But I am not sure if I am over thinking this.
    This a solution I have been considering

    Any comments about this idea is greatly appreciated

  6. LItoadk | | #6

    I was wondering if anyone has comments on my last post regarding crawl air circulation

    I am strugging with understanding if we need an active system to circulate air or would a simple transfer grill suffice

  7. bennettg | | #7

    I'm with Malcolm. Why wouldn't putting a baseboard unit in the crawl work? They're dirt cheap.

    To move air from the living space to the crawl, I think you're going to need a fan to move the lighter, warmer air down to the cooler crawl. And something to control it. And a return path...

  8. the74impala | | #8

    Get a dehumidifier, that will keep it warmer and dry. Just need somewhere for it to drain and not get back in the system. Check out crawlspace ninja on youtube.

  9. brad_rh | | #9

    Do you need to add heat to the crawl space? If the perimeter walls are insulated, and there is no insulation in the living space floor, I think you will be a long ways from 32F

  10. Expert Member
    BILL WICHERS | | #10

    Looks like you’re in an area of mixed climate zone 5 and 6. You should really have more than 1” of EPS (which is only about R4) on your crawlspace walls. Code for a long time was R10, it’s now R15, and those are minimums.

    That said, a circulation fan and some ducts to the living space is probably the lowest operating cost option. You could also put a small electric heater in the crawlspace, just make sure it’s intended for permanent service — don’t use a plug-in space heater here.


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