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Is a heat-pump water heater in Zone 7 worth it?

matthewberger94 | Posted in Energy Efficiency and Durability on

I’m currently designing a highly efficient 2 bedroom 1080 sqft house. Right now I am wondering if a heat pump water heater would pay itself off before it needs to be replaced. Also, the mechanical room would only be 3’6″ x 7’6″, not big enough size for manufactures recommendations of 10’x10’x10′

My question is how could I run the numbers to see if buying one is a good investment?

Why aren’t there any systems that have an outdoor unit and an indoor unit like HVAC air-source heat pumps? HVAC systems maintain a COP of 2.0 even during -5*F weather? Would the COP of a water heating system be less than 1.0 during winter months due to the delta-T in-comparison to an HVAC system? Say from -15*F to 70*F = 85*F delta-T for the HVAC system and -15*F to 120*F = 135*F delta-T for the water heating system?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Matt,
    The limiting factor in your case is the size of the mechanical room. It's too small, so I would eliminate a conventional heat-pump water heater from your wish list.

    If you decided to make your house and your mechanical room a little bigger, you would probably find that the incremental cost of the heat-pump water heater was a good investment, but the answer depends on how much hot water your family uses (large volume users see a faster payback) and your local electric rates (payback is faster in areas where electricity is expensive).

    If you want to purchase a split-system heat-pump water heater, you probably can. Here is a link to an article about the Sanden heat pump water heater: Split-System Heat-Pump Water Heaters. It's not a cheap product, however -- the cost is about $3,700, so expect the payback period to be very long.

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