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Heat pump water heater and pantry with long duct run

mjezzi | Posted in General Questions on

I’m building a home that’s roughly 60’x25’. I have my heat pump water heater located on the second floor and my 4’x2’ kitchen pantry on the opposite side of the main floor. I’d like to run a long insulated duct  channeling the heat pump’s cold exhaust air to the pantry. It would be a straight shot 60’ run. Over the 60’, I can slope the duct down by a foot. 

I realize that the temp will not be consistent, but even if it cools the room at all, it can only help. The pantry will have dry herbs for the most part.

Is there any chance that this would  work?

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  1. GBA Editor
    Martin Holladay | | #1

    Did you see the article on this topic that was published here on GBA a few hours ago? Here is the link: "Attaching Ducts to a Heat-Pump Water Heater."

    1. mjezzi | | #2

      Yes, that’s what made me think of the question. I’ve been thinking about this for a while. I just don’t understand thermodynamics and static pressure enough to know if the cold air will make it to the pantry.

  2. Aedi | | #3

    It would not work. 60 feet is a long run. A heat pump water heater runs intermittently, so the duct will warm to room temperature between each cycle. The cool air then needs to cool the inside of the duct before it even has a chance to cool the pantry, and by the time it does the cycle will probably be over. Considering how meager the cooling effect would be even if the HPWH was placed inside the pantry, buying nearly 100 dollars of duct is certainly not worthwhile. And that's ignoring all the pressure issues and how effective the insulation would have to be.

    1. mjezzi | | #4

      Thanks Aedi. That’s exactly what I needed to hear. I’ll officially nix the idea of using a HPWH to cool a pantry.

      1. charlie_sullivan | | #5

        Just to add to Aedi's reply--you could solve the static pressure issue by using a giant large-diameter duct. But then you'd guarantee that you'd only be cooling the giant volume of the duct, and not the pantry.

        If you want low-energy pantry cooling and an engineering project, you could run your incoming cold water supply to a heat exchanger in the pantry before it goes to the water heater and the rest of the house. That's probably not worthwhile either but it's closer to being worthwhile.

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