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Community and Q&A

Best water heater for Hawaii?

user-7264467 | Posted in General Questions on

Is it more cost-efficient to install a heat-pump hot water heater or thermal solar in Hawaii? Our energy costs exceed $0.30 per kilowatt hour, and significant rebates are available from the state and feds making the solar cost around $2,000 after tax credits. Any help appreciated many thanks.

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  1. canada_deck | | #1

    Questions that will help:
    - How many people in the household?
    - How big is your current water heater and is it big enough for your needs?
    - What kind of roof do you have?
    - Is natural gas an option?

  2. user-7264467 | | #2

    Three people, sometimes four. We do run out of hot water with our current electric heater from time to time if folks shower back-to-back or run washer/dishwasher concurrently.

    Have a Whirlpool 50 gal electric water heater from 2001. We have a three-story pole house, so the heater is located on the bottom floor in a carport that we intend to turn into storage in the next year. All the living space is on the second and third floors.

    We have a comp roof. We plan to reroof with metal and install PV in the future and would rather not install thermal solar on the roof.

    Yes, natural gas is an option, but we only get propane here in the islands. Hawaii Energy, a government program to help you save energy, recommends the solar hot water.

    Thanks for your help!

    1. this_page_left_blank | | #5

      Just FYI, natural gas and propane are two different things. Natural gas is generally piped direct to your house and also generally way cheaper than propane.

  3. tommay | | #3

    Get yourself a couple rolls or more of 1" black poly water service pipe, 100' per roll, lay it out in the sun for either an outside shower or preheat for your HW heater. A lot cheaper than conventional solar HW panels especially since you don't have to worry about freezing.

  4. FourForHome | | #4

    The Rheem Hybrid (heat pump) water heater at Home Depot has a COP of 3.7 (1kW of power delivers 3.7kW worth of hot water.
    If most of your hot water use is during sunshine hours, solar panels + HPWH would be efficient. It wouldn't be cost effective to power a standard water heater (COP of 0.93) with solar panels - it would take 4 times the number panels to heat the same amount of water.
    Additionally, if you brought the HPWH into the conditioned space, it would provide essentially free space cooling while it is running (and deliver hot water quicker when it's near the faucets.)
    I think the experts here will tell you that solar panels beat out solar hot water cost/benefit-wise several years ago.

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