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I am working with an HVAC contractor to replace my current gas-power water heater tank with a heat pump water heater. It will be located in an unconditioned utility closet with a door connected to the outside (see photos below). I plan to replace the door also.

The closet itself is quite small, so I need some air ventilation. I wanted to get some other opinions about what sort of door or vent I can get that will be sufficient. Will a door with a small louver work? How big does the louver need to be and where should it be located? Could I just use a vent instead and have a solid door? Any suggestions would be welcomed, thanks.

Outdoor utility closet door Outdoor utility closet with gas water heater

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    The heat pump water heater manual will have the details on space needed, vent sizes, etc.
    – Armand
    Commented Mar 29 at 23:58
  • 2x200 cfm louvers should work one at the top one at the bottom of the door. The problem will be the bugs can come in
    – DIY75
    Commented Mar 30 at 0:21
  • why do you need air ventilation?
    – Tiger Guy
    Commented Mar 30 at 4:37
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    @TigerGuy HPWHs need airflow to warm their evaporator (air-side) coils or else they'll just frost up and stop working
    – ThreePhaseEel
    Commented Mar 30 at 4:48

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Presumably you are in a location where it does not get too cold outside?

The HPWHs I looked at had vent kits available for intake and exhaust. IIRC that one used 8" vent pipe, but yours might vary. My area is too cold to use outside air for intake, at least on the HPWHs I looked at. I think they require 37°F minimum for intake air temperature.

If you wanted you could get by with just door vents, or a door vent for intake and connecting the cold output air to a vent pipe for better efficiency (not mixing the cold exhaust with the intake air in the closet.) Fully ducted intake and exhaust is also reasonable, particularly if you have something like a hot attic space to draw the intake air from.

I'd be replacing that flex duct for the dryer with rigid, too.

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    We are in the Bay area of California, so not too cold.
    – Duncan Rager
    Commented Mar 30 at 15:13

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