We have our furnace in the crawl space so air immediately travels to the upstairs first, while our thermostat is downstairs. Given that is is pretty cold out, our heater runs and causes the upstairs to be substantially warmer than the downstairs. I am closing our upstairs external vents so that i can push air downstairs, but two of them are whistling, and these two happen to be the closest/shortest distance from furnace to the vent exit. Is there something I can do to correct this? One has air pushing out through the handle that opens and closes the vent, while the other is coming through the vent itself (not perfectly sealed). I am curious if it's fixable given that the distance between these two vents and the furnace is so short that the air pressure being created is why air is finding a way out and that I am basically screwed.

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Posted by The Mick

Member since Oct 2010

44897 posts

Posted on 12/15/25 at 1:13 pm to BilbeauTBaggins

Probably a dumb question, but is there a damper you can adjust more air to downstairs? (or maybe can install a diverter of some kind)

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Posted by BilbeauTBaggins

probably stuck in traffic

Member since May 2021

7661 posts

Posted on 12/15/25 at 1:24 pm to The Mick

I can do that in the crawl space by adjusting the vent against the furnace. not ideal because this cold front isn't going to last forever and it is indeed a "crawl" space that I would rather avoid going into often. I guess the permanent solution would be to add motorized dampers.

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Posted by gumbo2176

Member since May 2018

19390 posts

Posted on 12/15/25 at 1:29 pm to BilbeauTBaggins

Chances are there is an adjustable damper in the supply plenum to all the vent lines coming off of it and you can adjust them at that point.

Not doing so is still allowing plenty of air to go to the upstairs registers and that is why they are whistling after shutting them down a bit.

Yes, it's inconvenient if your crawlspace is tight, but you either go find out if there are dampers at that point that can be adjusted or live with the noise.

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