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?