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  1. #1

    Confused heat pump vs. heat strips in air handler

    Can someone explain why it is more efficient to heat with a heat pump than to heat simply with electric heat strips in the air handler?

    We'd like to put in an AC unit, a gas furnace, and to use electric heat strips in the air handler in place of a heat pump. This way we can still heat most of the time with electricity, but we'll do it through the heat strips - not the heat pump. Everyone says this is not efficient, but why is this so technically?

    Thanks.

  2. #2
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    ok first of all looks like you have too many components to your system (unless you have multiple systems)

    ok in short the reason why a heat pump is cheaper to operate is it moves heat from outside to inside and it takes 1/3 or less power to do it verses spinning your meter to make heat out of electric resistance coils

  3. #3
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    One electric heat strip will pull more power than the entire heat pump.

  4. #4
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    Quote Originally Posted by bonyadlou View Post
    Can someone explain why it is more efficient to heat with a heat pump than to heat simply with electric heat strips in the air handler?

    We'd like to put in an AC unit, a gas furnace, and to use electric heat strips in the air handler in place of a heat pump. This way we can still heat most of the time with electricity, but we'll do it through the heat strips - not the heat pump. Everyone says this is not efficient, but why is this so technically?

    Thanks.
    You will get approximately 3 BTU of heat for every Kilowatt of electricity used on a heat pump, but only 1 BTU for each KW used on electric heat. It will take at least 3 times as much power/money to heat with strip heat as a heat pump. This calculation will also depend on the efficiency of the heat pump.
    If you have a gas furnace why do you want to use the a heat pump. I'd prefere the gas system over the heat pump.
    [FONT="Comic Sans MS"]merken1[/FONT]

  5. #5
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    Quote Originally Posted by merken1 View Post
    You will get approximately 3 BTU of heat for every Kilowatt of electricity used on a heat pump, but only 1 BTU for each KW used on electric heat. It will take at least 3 times as much power/money to heat with strip heat as a heat pump. This calculation will also depend on the efficiency of the heat pump.
    If you have a gas furnace why do you want to use the a heat pump. I'd prefere the gas system over the heat pump.

    You sure about those btu's? Last I checked a kilowatt was equal to 3,413 btu's did I miss something?


    I agree with the 3 times as much heat moved with the heat pump as opposed to resistance heaters though.

  6. #6

    WHY is this so?

    Thanks for everyone's replies. But WHY do the heat strips pull 3 times as much power as the heat pump? How is it possible if the unit is outside and the heat gets cooled as it comes into the house? The heat strips are already in the air handler iand also have no extra components that use electricity. It seems contradictory.

    Also, how much more efficient is a gas furnace over the heat strips? We live in southern Virginia.

    Thanks.

  7. #7
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    Because you use actual wattage to "make" heat. In a heat pump it uses a median (refrigerant) to transfer heat. It only rquires a 1/3 of the power (or close because it varies) to operate the "pump". However when your heat strip comes on it converts electricity into heat which comes out to 3.413 btu per watt.


    I use the word make because your not actually making heat but converting electricity into usable heat.


    How much more efficient depends on your kw/hr charges. And the cost of natural gas and what size it is and what temp. you like to keep the house at. The general rule is if your power is dirt cheap then heat pumps can be an option. However this varies from state to state and the operating conditions the heat pump would be in. Wouldn't really be practical if your average outside temps were 17ºF but if your closer to 32º or so on average then it's an option to at least look at. When the heat pump goes into defrost and has a electric heat strip the outside unit will cut the fan off and go into cooling mode to melt the ice that has built up. During that time in defrost mode your electric strips will come on to help keep you warm instead of blowing ice cold air for the time it takes to melt the ice.

  8. #8
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    Quote Originally Posted by bonyadlou View Post
    Thanks for everyone's replies. But WHY do the heat strips pull 3 times as much power as the heat pump? How is it possible if the unit is outside and the heat gets cooled as it comes into the house? The heat strips are already in the air handler iand also have no extra components that use electricity. It seems contradictory.

    Also, how much more efficient is a gas furnace over the heat strips? We live in southern Virginia.

    Thanks.
    It is much more efficient to convert electricity into mechanical energy than heat energy. In a heat pump, the properties of mechanical refrigeration allow us to remove heat from a cold place(essentially cooling the outside air further) and deposit it into a warm place (essentially warming the inside air further).

    Mechanical refrigeration depends on the fact that if you raise the pressure of a gas... any gas... you automatically raise the temperature as well. Most people know that there is a compressor in air conditioning and/or refrigeration... that is the purpose of the compressor: to raise the pressure/temperature of the gas... Now it is only a case of controlling where it goes and what it does, including using the same system for air conditioning just by controlling the flow.
    Is this a Fabreze moment? C.Y.D. I'm voting white elephant. 2.
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  9. #9
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    Big juju, much magic.
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  10. #10
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    Quote Originally Posted by bonyadlou View Post
    Thanks for everyone's replies. But WHY do the heat strips pull 3 times as much power as the heat pump? How is it possible if the unit is outside and the heat gets cooled as it comes into the house? The heat strips are already in the air handler iand also have no extra components that use electricity. It seems contradictory.

    Also, how much more efficient is a gas furnace over the heat strips? We live in southern Virginia.

    Thanks.
    The 3 times per KW is the way the power is used in the application of the equipment. It is more efficient to run a heat pump (motor) than it it is to heat with electricity( strip heat), but that is based on the outdoor temperture.
    If you live in Virginia you are on the border line for the efficiency level for a heat pump. The efficiency rating on a heat pump is based on a 55 degree Out Door air tempertature. As the out door temperture drops the efficiency levels of the unit also drop. The temperature where the heat pump and the strips are equal are around 40 degrees. Under that temperature the heat pump will actually use more than 1 KW to produce one BTU. You will also have to add in the defrost cycle as at that temperature the outdoor coil tends to freeze up fairly quick.
    All told because of the complexity of the systems if gas is available I would use it in lieu of a heat pump. I'm probably opening a can of worms here , but that is my personnel opinion.
    [FONT="Comic Sans MS"]merken1[/FONT]

  11. #11
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    Quote Originally Posted by BigJon3475 View Post
    You sure about those btu's? Last I checked a kilowatt was equal to 3,413 btu's did I miss something?


    I agree with the 3 times as much heat moved with the heat pump as opposed to resistance heaters though.
    You are correct in that a BTU is equal to 3,413. If a heat pump uses 1 KW it will produce approximately 3 BTU (10,239). If a strip heater uses 1 KW it will produce 3,413 BTU.
    On the heat pump this is based generally on a 55/60 ODA degree temperture because as the ODA temp decreases the efficiency level drops. This is where the COP, SEER, etc rating are developed.
    [FONT="Comic Sans MS"]merken1[/FONT]

  12. #12
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    If you are in a mild winter climate with low electric rates, the heat strips can be a better option IMO. I state this because a heatpump's life expectancy is alot lower than a straight a/c with heatstrips, and there a more things that can go wrong with a heatpump over the course of it's life. In a mild winter climate, I'd opt for the highest seer a/c I could afford with heat strips. JMO.
    If everything was always done "by the book"....the book would never change.

  13. #13
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    Hmm

    Heating with a heat pump takes gettin use to they are sized most the time for cooling so when they are in the heat mode they will only match one third of your heating requiment.
    There are many different manufactures with offer's and modifications avalible to increase the effency's of there heat pump units I like to At 27 degrees at nighttime get ready for some supplemental heat(gas or electric)
    Around 18 dgrees the heatpump will defrost every 20min an you will lose what you gained.
    But they cost less than a high effency airconditioner an you can use the unit to save on some of your heat cost

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