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  1. #1
    Join Date
    Jun 2007
    Location
    louisville ky
    Posts
    107

    price to run gas vs heatpump

    hi i have a 95% gas furnace and a 14 seer 8.2 HSPF heatpump. i was looking at my gas and Electricity website. it looks like this winter it will be cheaper to run the gas furnace can that be true. i live in louisville ky. where is the website http://www.eon-us.com/rsc/lge/res_heating_costs.asp if i run the heatpump should i set my switch over temp to 40?

  2. #2
    Join Date
    Sep 2002
    Location
    I don't know
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    2,897
    Compare gas + electricity rates and efficiency.

    Your heatpump is capable of providing 3+ units of heat for every unit of energy consumed. The info on that website applies to heatpumps will electric backup as opposed to dual fuel systems.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  3. #3
    Join Date
    Jun 2007
    Location
    louisville ky
    Posts
    107
    is there a website i can put my info in and see what will be cheaper?

  4. #4
    Join Date
    Sep 2002
    Location
    I don't know
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    2,897
    Not that I know of.

    Relative operating costs at different outdoor temps can be calculated manually or with a spread sheet.

    Chances are that your heatpump will start losing ground far before it becomes more expensive to operate than the furnace.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,774
    By the rates from that site.

    As long as your heat pumps COP is at or above 2.6, the heat pump is cheaper.
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  6. #6
    Join Date
    Sep 2006
    Posts
    1,253
    Quote Originally Posted by chrism9232 View Post
    is there a website i can put my info in and see what will be cheaper?
    Determine your total cost of each energy source by dividing the actual cost on the invoice (which includes all taxes, surcharges, and other add-on expenses not included in the quoted rate) by the amount of energy delivered.

    Use a COP for the heat pump in a range of 2.5 to 3.0 when inputting your energy cost at this site: http://www.warmair.com/html/fuel_cost_comparisons.htm

  7. #7
    Join Date
    Jun 2007
    Location
    louisville ky
    Posts
    107
    if i did it right it looks like any time my heatpump is above 3.0 cop it will be cheaper

  8. #8
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Here's the math.

    Compare the cost of 1 million btu's of heat.

    Gas furnace w/gas at $.633 per ccf, 95% AFUE:
    (1,000,000 / 100,000 btu per ccf) x .633 / .95
    = $6.66

    Heat pump w/electricity at $.064 per kw-hr delivered price, COP = 3.25 at 35F:
    (1,000,000 / 3414 btu per kw-hr) x .064 / 3.25
    = $5.76

    The heat pump is 13.4% cheaper than the gas furnace for the same 1 million btu's at 35F ambient with COP = 3.25.

    As the ambient temps increase from the 35F example, COP increases, and the heat pump is even cheaper to run.

    Take care.

  9. #9
    Join Date
    Jun 2007
    Location
    louisville ky
    Posts
    107
    is that counting defrost? my heatpump defrost every 60 min and the gas is on first stage when the heatpump is defrosting.

  10. #10
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by chrism9232 View Post
    is that counting defrost? my heatpump defrost every 60 min and the gas is on first stage when the heatpump is defrosting.
    No. Does not include the cost to defrost.

  11. #11
    Join Date
    Jul 2003
    Location
    Philadelphia Pa.
    Posts
    461
    Quote Originally Posted by gary_g View Post
    Here's the math.

    Compare the cost of 1 million btu's of heat.

    Gas furnace w/gas at $.633 per ccf, 95% AFUE:
    (1,000,000 / 100,000 btu per ccf) x .633 / .95
    = $6.66

    Heat pump w/electricity at $.064 per kw-hr delivered price, COP = 3.25 at 35F:
    (1,000,000 / 3414 btu per kw-hr) x .064 / 3.25
    = $5.76

    The heat pump is 13.4% cheaper than the gas furnace for the same 1 million btu's at 35F ambient with COP = 3.25.

    As the ambient temps increase from the 35F example, COP increases, and the heat pump is even cheaper to run.

    Take care.
    Hmm I just plugged in my gas and electric rates into these formulas. I guess I did it correctly. Is there a chart or formula to use that will show how the COP changes as the temperature drops?

  12. #12
    Join Date
    Sep 2002
    Location
    I don't know
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    2,897
    No.

    Performance greatly varies between different models and manufacturers.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  13. #13
    Join Date
    Oct 2005
    Location
    Pacific Northwest
    Posts
    2,261
    Quote Originally Posted by gary_g View Post
    No. Does not include the cost to defrost.
    That's a big deal with systems that don't utilize a demand defrost control.

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