I'm aware that my exterior crawlspace vents are to be opened when it goes over 70F outside and closed when it goes below 40F. However, what's the protocol for the crawlspace vent that goes into the attached, unheated garage?

This crawlspace vent is near the garage door, so it likely gets blasted with nice subzero air during the worst of the Winter. Yet, the garage itself does not freeze internally within about 3-4 feet of the vent, and the garage interior air temperature stays above 40F overall even on the worse days we see (-15F for a week or so at a time is as bad as it really gets here). I'm just not certain if I should close the vent to try to protect the water lines in the crawlspace from that cold garage air or if I should leave it open to allow humidity somewhere to go?

  • 1
    If your furnace and water heater are in the garage this may be there for fresh air (gas appliances).
    – Ed Beal
    Oct 30, 2016 at 14:59
  • In some jurisdictions, the divider between interior space and garage must be airtight, to prevent CO migration into the living space...
    – DJohnM
    Oct 31, 2016 at 16:41
  • The fresh air comment is interesting, but don't garages normally leak far more air than a house already (and gas appliances are fine in the house)? Oct 31, 2016 at 17:55


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