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  1. #1
    Join Date
    Jun 2008
    Posts
    13

    How do I calculate heat pump savings?

    I need to replace my AC and am thinking about going with a heat pump system. How do I go about calculating the savings from a heat pump?

    Currently, I use about 1500 therms per year to heat the house and about 6400 kwh for AC. I live near Washington DC. where we get about 4000+ Heating degree days and about 1500 cooling degree days. Average lows in January are in the 20 degree range. Average lows in April/October in the 40s.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,320
    This will give you an idea.
    http://www.hvacopcost.com/
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  3. #3
    Join Date
    Jun 2008
    Posts
    13
    Quote Originally Posted by beenthere View Post
    This will give you an idea.
    http://www.hvacopcost.com/

    That is a great calculator, and it implies I would save about $1,000 per year. However, I would like to be able to do the calculations myself, because I tend not to trust other people's calculations. (And yes, I do have an engineering background ). Are there any good reference sites which would show me how to do the calculations?
    Last edited by jza29970; 06-25-2008 at 12:33 PM. Reason: add clarity

  4. #4
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by jza29970 View Post
    That is a great calculator, and it implies I would save about $1,000 per year. However, I would like to be able to do the calculations myself, because I tend not to trust other people's calculations. (And yes, I do have an engineering background ). Are there any good reference sites which would show me how to do the calculations?
    You can figure the price of 1 million btu's among different fuels and compare them for a percentage of savings.

    Example:

    Cost of 1 million btu's for natural gas at $1.20 per 100 cubic feet, 80% efficient furnace:
    (1,000,000 btu / 103,000 btu per ccf) x $1.20 / .8
    = $14.56

    Cost of 1 million btu's for heat pump with electricity at 12 cents per kw-hr, COP = 3.25 at 35F ambient:
    (1,000,000 / 3413) x .12 / 3.25
    = $10.82

    Cost savings from using heat pump = 25.7%.

    Note that below the balance point of the house (32F or so), auxillary heat will be required for the heat pump. This is not included in the calc, neither is the aux heat required for when the heat pump goes into a defrost cycle.

    Take care.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,320
    There are no sites that are set up to do an accurate(in depth) operating cost comparison.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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