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Community and Q&A

Best electric water heater for Warmboard radiant floors (and DHW)?

Emily Griffen | Posted in Energy Efficiency and Durability on

I am building a 2000 square foot, well-insulated (but not super-insulated) house in coastal Northern California, which is a mild, heat-only climate. We are using Warmboard radiant floors (it is already installed, so no need to try to talk me out of it).
We do not have access to natural gas, would rather not use propane, and have a solar PV system we’d like to use to its full capacity. As a result, I’d like to use the most efficient electric water heater solution for both the Warmboard and DHW. We have a large, insulated attached garage that seems perfect for a heat pump water heater (it rarely drops much below 40 degrees outside, and the garage likely would not), but some of the threads I’ve read here suggest that it would not work well for Warmboard, and our plumber is concerned about an 80 gallon heat pump water heater being sufficient both for Warmboard space heating and DHW (for a three-bedroom, 3-person household).
Any advice on what type of electric water heater or heaters to use, and whether to attempt to use one water heater for both Warmboard and DHW (an indirect system with a heat exchanger) or to get a separate heater for each (and if so, what)?
Many thanks in advance.

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  1. GBA Editor
    Martin Holladay | | #1

    The only device I know to meet your needs is the Daikin Altherma air-to-water heat pump. It is frightfully expensive. Expect to pay between $20,000 and $26,000 for this system.

    You would be much better off heating your home with a couple of ductless minisplit units.

    Air-source heat pumps are a poor match for radiant floor heat distribution, for a variety of reasons. Your two goals are somewhat incompatible: using an air-source heat pump for space heating, and using hydronic distribution.

    The moral of the story: you need to settle these issues before construction begins.

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