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Heat Pump Hot Water Heater Ventilation Requirements

I am interested in installing a Heat Pump Hot Water Heater but it would need to go into a "closet" in the basement. The closet itself is 88 cubic feat but it has double louver doors to the main area of the room. The room in total with the closet is about 862 cubic feat. Additionally, the closet has a partially obscured 12x12" open "window" to a crawl space on the other side of the house. Because I living in the Northeast, I plan to install a damper controlled duct that would allow me to switch between exhausting the cold air to the exterior in the winter and switch it to the internal space in the summer.

1. Is 862 cubic feet sufficient?
2. Is the Louver door (and the "window to the crawl space") enough to allow for air exchange to the HPWH or should I add a dedicated input vent from the main area to the input of the HPWH?
3. Has anyone played with 3D printed vent kits from Rheem? The ones the sell are absurdly expensive (for molded plastic) and only exhaust in one direction.

Attached are photos of the doors, the crawl space window (it looks like it is just a screen to a wall of dirt but that is just a trick of the photo...the stuff behind it is at an angle), and the top of the current HW).


  • pecmsg
    pecmsg Member Posts: 4,895
    I highly doubt thats enough "Free Air" to operate that unit without the closet getting cold.

    Contact the manufacture.
  • JakeCK
    JakeCK Member Posts: 1,360
    You're going to have to duct it. You might be able to get away with just ducting the intake and letting it exhaust into the closet. Yes the closet will be cold, around 50F, but the supply air to the hx will be much warmer.

    Also I wouldn't worry about ducting the exhaust outside, it won't affect the temperature of the whole basement much. I speak from experience.
  • ethicalpaul
    ethicalpaul Member Posts: 5,740
    I agree with @JakeCK don't even bother trying to duct it outside. It takes so little heat from the room to heat your water, it's kind of surprising. Winter or summer, I don't notice any difference at all in the basement.

    Honestly I would try it with just the louvered doors, they might be fine. You can always leave a door open until you add a duct if it actually is a problem.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,338
    Hi, I'd do everything you can to keep inlet and output air-flows separated when in a small room. I've had experience where the cold output was getting sucked into the input, greatly reducing the efficiency of the units. This could mean ducting to the louvered door and gasketing where it meets the door. This prevents the dreaded mixing. >:)

    Yours, Larry