I am wondering whether it is ok to vent the hot air from a portable air conditioner to the same duct where the bathroom air vent is in an apartment considering that the apartment block removes the supposedly humid air from all the bathrooms using a HVAC system in the building?

  • Aside from any question regarding legality, consider the air flow from the portable AC vs. the draft in the bathroom vent. See inspectapedia.com/aircond/Air_Flow_Rates.php . My hunch is that the AC puts out vastly more air than the bathroom vent can remove. Commented Jun 16, 2023 at 18:35
  • Do you mean a single-hose floor-standing portable A/C ? That might work, very poorly, if you locate the hose NEAR the vent but do not seal it to the vent. That way the vent ingests as much air as it was designed for, mostly the warm humid air from your machine but you're not forcing air into your neighbors' apartments. Whether that will have any cooling effect on the bathroom IDK. It may mostly produce noise, and consume electricity and it may even net net heat the room!
    – jay613
    Commented Jun 16, 2023 at 19:15
  • I don't mean blowing air near the bathroom vent but rather running a duct hose to the same duct behind the drywall on the ceiling where the bathroom ventilator is blowing air into. The other end of the duct hose will be run to a convenient location coming out of the drywall where it can be connected to the portable AC.
    – ld_pvl
    Commented Jun 16, 2023 at 19:25
  • Sounds like it might work, at least about as well as those awful portable A/C units ever 'work'.
    – KMJ
    Commented Jun 16, 2023 at 19:44
  • Is it a large building with shared ventilation ducts and an exhaust on the roof, or does each unit have its own ducts that exit via some nearby wall? If the latter it might work. Maybe. If the former, it is probably illegal, it certainly should be.
    – jay613
    Commented Jun 16, 2023 at 19:55

1 Answer 1


Sounds like great idea.

Probably should verify that the bathroom exhaust is exhausting directly to the outside.

Look up the AC output in CFM, vs the duct size, vs the exhaust fan size.

It sounds more complicated than it is to verify before proceeding.

Technically it should work, but esthetics of it (having a ugly pipe going to the ceiling) probably stoped others from doing it

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