It is acceptable to vent a bathroom exhaust fan into a crawlspace?
The crawlspace in question is uninsulated, has a dirt floor, and varies in height between 5' and 7'.
The vent would enter roughly in the middle of about 1000 sq ft or floor area.
The furnace and water heater (both gas) are located fairly close.

  • your furnace and water heater are in your dirt floor crawlspace?
    – DA01
    Nov 9, 2017 at 19:08
  • @DA01 - Well, the furnace is sitting on a small concrete pad and the water heater on blocks, but that's it.
    – brhans
    Nov 9, 2017 at 19:11
  • Interesting. Perhaps that's a regional thing.
    – DA01
    Nov 9, 2017 at 19:14

1 Answer 1


No, at least not under the international residential code (IRC):

M1501.1 Outdoor Discharge

The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.3. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

And more specifically:

M1507.2 Recirculation of Air

Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.

The reasoning is simple: the exhausted air is likely to contain a lot of moisture, and will therefore result in mold growth in your crawlspace. Your local codes may differ depending on where you live, but it's still not a good idea.

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