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Are there tankless heat pump water heaters?

BlueSolar | Posted in Green Products and Materials on

Hi all — Are there tankless heat pump water heaters? If so, where can I find them? Web searches haven’t borne fruit.

If they don’t exist, is it something about the way heat pump water heaters work that makes tankless models infeasible?

Thanks.

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Replies

  1. DCContrarian | | #1

    I can't say definitively that they don't exist, but they're not a good application. Domestic hot water consumes BTU's at a pretty hefty rate, but typically it is only used sporadically throughout the day. Just to throw out some numbers, let's say your shower uses two gallons per minute of water, which entered the house at 50F and comes out of the shower at 100F. That's an instantaneous rate of 48,000 BTU per hour or 14,000 watts.

    However, let's say you only use 100 gallons of hot water per day. You would only be heating water at that rate for 50 minutes a day, the other 23 hours and 10 minutes your heater sits idle. With a tank you can heat that water slowly and save it up for when you need it, you'd only need a heater with a capacity of 1667 BTU/hr or slightly under 500 watts.

    Heat pumps are better suited to continuous, constant loads.

  2. Expert Member
    Akos | | #2

    Its a question of BTUs. It takes A LOT of btu to bring water from cold up to shower temperature at a reasonable flowrate, most tankless units are around 150k to 200k btu. In comparison your average heat pump water heater has a 4k btu heat pump (15 to 20 times smaller).

    The physical size of the required heat pump would be about the size of a small room, never mind the cost.

    Then there is the question of where this heat would be pumped from. Running a 200kbtu air source heat pump inside your basement would cool it down to freezing temperatures in seconds. You would need a fairly large thermal mass like a big water tank.

    Now you have a room sized heat pump connected to a large closet sized water tank. Not the most compact water heater.

    I think the existing tank heat pump water heaters are a pretty good compromise. It would be nice if they would put out a bit more BTU and handled lower temperatures so you could steal a bit of output for space heat.

  3. GBA Editor
    Brian Pontolilo | | #3

    I've heard nothing of tankless heat pump water heaters, and as the first two posts point out, they seem unlikely. Even tank-style heat pump water heaters are not gaining a whole lot of traction in the industry. One emerging technology is gas-powered heat pump water heaters, which are expected to be hitting the market in the next few years. Check out this article for more on the most efficient water heaters and what manufacturers are currently developing: Choosing an Efficient Water Heater

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