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Community and Q&A

Wall-mounted bath fan in an uninsulated brick wall

Sean Lewkiw | Posted in Mechanicals on

Hi, I live in a 100 year-old row home in Montreal, (where it can easily go down to -20 in the winter). The walls are double brick with no insulation, luckily most walls are abutted by an adjoining home. There are a few exposed walls in bump-outs though. One of those walls is our master bathroom, which has no fan. I want to install one.

I understand that ideally it would go through the roof. However, we have a flat roof with about two feet of attic space, and no access to the attic. (Frankly, what’s up in that two-foot space is a total mystery.) In a few years time we will have to re-do the roof, but until then I have no interest in messing with it by making a giant hole through it.

So, I’m thinking of installing a wall-mount fan. My question is, will this just be a massive source of heat loss due to the fact that there will only be about six inches of duct between the inlet and outlet? I can’t imagine a bath fan damper being a great insulator. Is there another approach we should consider?

Thanks in advance for any help!

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  1. GBA Editor
    Martin Holladay | | #1

    Wall-mounted exhaust fans do, indeed, have more customer complaints about air leakage than ceiling-mounted fans that are vented through the roof.

    I don't think the fact that your brick wall is uninsulated is relevant -- it will not change the air leakage situation for better or worse.

    Whether or not the air leakage will irk you depends on many factors: the prevailing winds, whether the wall is sheltered, the strength of your heating system, and your personal sensitivities.

  2. Sean Lewkiw | | #2

    Thanks Martin. I guess I confused the issue by mentioning the lack of insulation... I was thinking the short length of ductwork would be the biggest issue, because any glancing wind will have a more direct route into the home, (ignoring the benefit of a duct flap). But as you said, that will be an issue, but how much of an issue depends on a lot of things. Thanks very much for your feedback.

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