I could not understand why my basement was constantly cold. I found by accident a cold blast of air coming through this vent from outside. Since this is in my utility room, next to my home forced air/header unit, I presume there is an important purpose of this vent. My utility room does have a slatted door, so if nothing with the vent, then could I use a solid door? Looking for options, please.

image of furnace and a duct

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    Many furnaces (particularly newer 90%) are designed to pull combustion air from outside directly rather than just getting air from the room, so you may want to look into that. But normally you would have one of: vent to outside, slatted door, some other gaps in the wall, so that there is sufficient combustion air. If that big round metal duct is "live", I would move the plastic buckets away from it. Actually, even if that duct isn't live, those buckets shouldn't be that close to the furnace in general. Dec 24, 2021 at 20:21
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    If you can cover it with fitting to attach a large hose to it and then have the hose make a loop going up before coming down, might help. An upside down P-trap shape. Cold air likes to sink down, not go up.
    – crip659
    Dec 24, 2021 at 22:05
  • Would try to also add a wind baffle on the outside. Something to stop the wind blowing inwards.
    – crip659
    Dec 25, 2021 at 13:24
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    Depending on type of furnace and water heater there are code requirements for how many square inches of vent that is required.
    – Ed Beal
    Dec 25, 2021 at 16:59
  • It appears you may have some exhaust fans running or warm air leaking from your home. This is made up with the air coming in somewhere such as your utility room vent. Since there is no indication of high efficiency hot water or furnace the combustion air they need is also coming in that tube.
    – Gil
    Jan 26, 2022 at 1:16

1 Answer 1


If the outside vent is sized properly, then you can change the slatted door to a solid door, maybe add weatherstripping. That would keep the outside air from reaching the rest of the basement.

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