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Thread: Cost comparison

  1. #1
    Join Date
    Aug 2006
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    Central MN
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    Cost comparison

    Which would be more efficient to operate. An air source heat pump or an electric plenum heater?

  2. #2
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    Jun 2005
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    The Gray Northwest
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    When you say "electric plenum heater" do you mean forced air w/resistance heat? If so, the heat pump wins.

  3. #3
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    We are looking at developing a duel fuel system.
    We would have a back-up propane furnace with an electric plenum heater in the duct work or an air source heat pump as primary heat
    I'm looking for which of the two primary heat source would be the most cost effective to operate

  4. #4
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    Jan 2004
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    Lancaster PA
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    Most heat pumps will provide more BTU's for the dollar then electric resistance heat, down to about -10*F.
    But, the actual BTU's per hour drop off as the OD temp gets lower.
    So, you will still need aux heat in most applications.

    Running a heat pump and the aux electric heat at the same time, is cheaper then electric resistance only heat.
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  5. #5
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    Electric resistance as the primary will cost you more then a heat pump as the primary.

    What is your electric rate, and how much does your propane cost per gal.
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  6. #6
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    Central MN
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    Beenthere,
    That is what I was looking for.

    Our current rates are:
    #2 fuel oil 3.689/gal
    Propane 2.169/gal
    Standard electric .072/kw
    Duel fuel .037/kw

    There is talk electric rate may increase

  7. #7
    Join Date
    Jun 2007
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    Quote Originally Posted by drift buster View Post
    Beenthere,
    That is what I was looking for.

    Our current rates are:
    #2 fuel oil 3.689/gal
    Propane 2.169/gal
    Standard electric .072/kw
    Duel fuel .037/kw

    There is talk electric rate may increase
    Cost for 1 milllion btus:

    Fuel oil (80% efficient furnace)
    (1,000,000 / 139,000 btu per gallon)($3.689) / .8
    = $33.17

    Propane (80% efficient furnace)
    (1,000,000 / 86,000 btu per gallon)($2.169) / .8
    = $31.53

    Standard electric (Heat pump, 35F outside temp, COP = 3)
    (1,000,000 / 3413 btu per kw-hr)($.072) / 3
    = $7.03

    Standard electric (Resistance heating)
    (1,000,000 / 3413)($.072)
    = $21.10

    At outdoor temps less than the balance point of the house (approx 30F), the heat pump will need aux heat which is not included in the above numbers.

    Not sure why the electric rate for "dual fuel" is half of the standard electric rate.

    What area of the country are you in?

    Best to you.

  8. #8
    Join Date
    Aug 2006
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    Central MN
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    Quote Originally Posted by gary_g View Post
    Cost for 1 milllion btus:

    Fuel oil (80% efficient furnace)
    (1,000,000 / 139,000 btu per gallon)($3.689) / .8
    = $33.17

    Propane (80% efficient furnace)
    (1,000,000 / 86,000 btu per gallon)($2.169) / .8
    = $31.53

    Standard electric (Heat pump, 35F outside temp, COP = 3)
    (1,000,000 / 3413 btu per kw-hr)($.072) / 3
    = $7.03

    Standard electric (Resistance heating)
    (1,000,000 / 3413)($.072)
    = $21.10

    At outdoor temps less than the balance point of the house (approx 30F), the heat pump will need aux heat which is not included in the above numbers.

    Not sure why the electric rate for "dual fuel" is half of the standard electric rate.

    What area of the country are you in?

    Best to you.
    Minnesota.
    The program the electic company has is if your primary heat source is electric and you have a back up other than electric they will reduce the electric rate.
    With this program they can interupt at any time during large electric demands up to 1/3 the heating season.

  9. #9
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    Jan 2004
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    Lancaster PA
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    You will still be saving over propane or oil, the other 2/3s of the winter.
    Most likely, the interuptions, will be during the colder months when your using the aux heat more oftern anyways.
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  10. #10
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    Mar 2008
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    Baltimore MD and Ridgebury PA
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    Quote Originally Posted by gary_g View Post
    Cost for 1 milllion btus:

    Fuel oil (80% efficient furnace)
    (1,000,000 / 139,000 btu per gallon)($3.689) / .8
    = $33.17

    Propane (80% efficient furnace)
    (1,000,000 / 86,000 btu per gallon)($2.169) / .8
    = $31.53

    Standard electric (Heat pump, 35F outside temp, COP = 3)
    (1,000,000 / 3413 btu per kw-hr)($.072) / 3
    = $7.03

    Standard electric (Resistance heating)
    (1,000,000 / 3413)($.072)
    = $21.10
    How do you figure on 86,000 BTUs per gallon for propane? The Dept. of Energy says 91,330. The American Gas Association says 91,600. It's not a huge difference but in the interests of accuracy it is important

    Propane (80%) should be:
    (1,000,000 / 91,000 btu per gallon)($2.169) / .8
    = $30.13
    Propane (90%) would be:
    (1,000,000 / 91,000 btu per gallon)($2.169) / .9
    = $26.45

    It's a tough call. Depends partly on the electric company maintaining the program you mentioned and to a large extent on future energy prices (relative to one another) which is a crap shoot However, you would save all through the summer and, as previously mentioned, when it cycles your compressor off during the winter you will likely be on the fossil fuel anyway due to temperatures. The propane is very close in price to the electric resistance heat provided you get a 90+ furnace. Also, you could operate the propane furnace during a power outage with a small generator... much less likely with the HP and almost certainly not with the electric resistance.

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
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    Talking > 1

    Quote Originally Posted by drift buster View Post
    Beenthere, That is what I was looking for.

    Our current rates are:
    #2 fuel oil 3.689/gal Propane 2.169/gal
    Standard electric .072/kw

    Dual dual $0.037/kw
    With such a huge operating co$t advantage,
    I would want to buy more than one heat pump.

    The Economic balance point becomes much lower than the Heat Transfer balance point. So, the cross-over set point should be in the low to mid 20's.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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