This is a very different question than venting a bathroom fan or clothes dryer to the attic (moist air), as the heat pump takes humidity out of the air (routes it to a condensation drain). The advantage of the heat pump is that it draws heat from the atmosphere, but the problem is that the exhaust from the heat pump is cold and in the winter months we don't need (or want) cold air in our laundry room where the water heater is.

The manufacturer (Rheem) gives a room size that is supposed to be large enough to absorb the cold exhaust air and otherwise recommends venting it out. They are generally silent on where "out" is, but I've seen posts on other sites where it's been vented to the attic.

Since it cools the air and removes humidity (through condensation on the pump), this would be an advantage to vent to the attic as it would both dry the air and provide cooling in the summer, yes? My only concern is that (historically) I would never vent anything to the attic, for somewhat obvious reasons, and now I'm faced with a potential advantage and an easier job since the attic is only 3 feet away.

  • I doubt that the humidity of the exhaust is zero. Do you have any reason to think you know what it actually is?
    – isherwood
    Commented Jan 30, 2020 at 18:34
  • No, you are correct about "zero", but I do have a small thermostat/humidity gauge that I could put next to the exhaust and compare with the existing humity (before any venting is installed).
    – GMisenar
    Commented Jan 30, 2020 at 18:37
  • I'd do that, but it's still not a great idea to be blowing air around. You could create vortexes that disturb insulation or potentially return dangerous gases to your living space. It almost certainly violates code and manufacturer guidelines.
    – isherwood
    Commented Jan 30, 2020 at 18:39
  • One other comment, I would install two vents, one is an intake from the attic and the other is an exhaust to the attic. They would be far enough apart that the air wouldn't just be cycled from one to the other.
    – GMisenar
    Commented Jan 30, 2020 at 18:39
  • 1
    I think pulling cold air from the attic in the winter would make the heater much less efficient. Heat pumps work by moving energy across a temperature differential, so they suffer when that is lacking (warm air from the room against the cold evaporator).
    – JPhi1618
    Commented Jan 30, 2020 at 18:59

1 Answer 1


The cold is just air cooled in the home and it has no more moisture than the house air in-fact it is dryer than the house air. I have vented 2 into Areas that are not conditioned , I think the attic is a good option as in the summer it will help cool that space. If you have plumbing in the attic I would choose a different location as this can help the pipes to freeze. I vented mine outside but that was a convenient location for me. You still need a drain for the moisture that builds up on the exchanger, also if a tight house you will need some makeup air allowed in normally at the furnace, my 1930’s home did not need additional vents but a Check needs to be done, the efficiency gain is reduced if inside the home so in my opinion it is a crock to require them.

  • Pardon my ignorance. What is a Chechen?
    – peinal
    Commented Jan 30, 2020 at 23:00
  • 1
    Looks like spell check took over check
    – Ed Beal
    Commented Jan 30, 2020 at 23:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.