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Community and Q&A

Musty smell

eunsek522 | Posted in General Questions on

Hi I just moved into an older home built in 1928.  When I turn on the AC, there’s musty smell coming from the vent.  Even when I don’t have the AC on, the musty smell from the basement comes through the floor vents. The basement is dry and I don’t see water spots. I’m not sure what the issue is and not sure who I should reach out to find out what’s causing the musty smell. 

Only thing I know is when home was inspected, the crawl space had mold, so it’s been mitigated and repaired.  The Crawal space entrance is through the outside under deck and the door does not seem to close all the way. 

Base on this information whom should I contact?

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  1. User avatar
    Dana Dorsett | | #1

    Have you checked the HVAC filters?

    Are the ducts tight? Are they reasonably well balanced?

    Where are you located (by US DOE climate zone)? Summertime "musty basement smell" in the "-A" climate zones is almost always a symptom of excessive outdoor air volumes infiltrating into the basement. Unbalanced duct systems can drive infiltration rates well in excess of "natural" stack effect drives. Band joists & foundation sills often leak more air than all of the window & door crackage in the rest of the house combined, and open flues for atmosheric drafted furnaces/boilers/water heaters as well as dryer vents with insufficient backflow prevention can all contribute to that outdoor air infiltration. It's worth finding and fixing as many air leaks into the basement and crawlspace that you can. (Fixing the door that doesn't fully close and weatherstripping it would be a good start.)

    Many basements will require mechanical dehumidification for at least part of the cooling season to keep the indoor basement humidity in check. The relative humidity need not be super low to work- 60% RH would be sufficient for most.

  2. Akos | | #2

    Whats the interior finish in the basement? Any flooring on the ground? Is your crawlspace enclosed or vented?

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