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  1. #1
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    Considering replacing a gas furnace with a heat pump

    Hi,
    We're considering replacing our old gas furnace and A/C unit with a heat pump.
    We're in Contra Costa Co., Calif., (climate zone 3, I believe).

    Wondering if there's a way to estimate the power consumption of the HP when heating so that we can compare the operating cost to what we're paying now for gas (we assume that a HP will be better than our existing A/C in cooling mode, so not too worried about that).

    Thanks for any advice.

  2. #2
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    Whats your current electric rate, and your current natural gas rate.
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  3. #3
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    Jan 2014
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    Food for thought only...Guessing you have a uncomplicated 80% furnace? and it has been troublefree for the many years being used only minimally during the year. Heat Pumps are much more complicated and run many more month during the year, to heat and cool. May or may not want to consider auxiliary heat if and when your HP is down for a period of time during your mild heating season?

    Certainly a modern energy efficient HP will use less amprege than an older system of the same tonnage if you decide to replace size for size and skip a load calculation. Even more so if you actually need a smaller system.

  4. #4
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    Guessing you have a uncomplicated 80% furnace? and it was troublefree for many years being used only minimally during the year. Heat Pumps are much more complicated and run many more month during the year. May or may not want to consider auxiliary heat if and when your HP is down for a period of time during your mild heating season?

  5. #5
    Join Date
    Mar 2019
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    Thread Starter
    Thanks for the reply.

    Our current gas rate is $1.63/therm.
    Current electric average (we have TOU) is $.28 kWh.
    We run the furnace about 16 hours/day during our heating season, Nov. - April.
    We use about 350 therms total during the season for the furnace.

    Cheers.

  6. #6
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    Okay, at the rates you posted, and the therms you posted.

    An 80% efficient nat gas furnace would be providing you 28,000,000 BTUs of heat for the season. At a cost of $570.50

    A heat pump would need to have a COP of 4.02 to be as cheap as a nat gas furnace. So it would only be cheaper to use when it was 60F or warmer outside.

    It takes 12.5 therms for a 80% gas furnace to output 1,000,000 BTUs of heat. It takes 293 KWHs of electric for resistance heat to output 1,000,000 BTUs of heat.

    12.5 times $1.63=$20.375
    293 times $0.28=$82.04
    $82.04 divided by $20.375=4.02 COP
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  7. #7
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    Thread Starter
    Thanks much. This is very helpful.

    I assume that if we replace our 80% efficiency furnace with one of 95% efficiency, the gas usage will decline by 15%?

  8. #8
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    Quote Originally Posted by East Bay Steve View Post
    Thanks much. This is very helpful.

    I assume that if we replace our 80% efficiency furnace with one of 95% efficiency, the gas usage will decline by 15%?
    If its sized right, it should, maybe even 20%.
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