Why is auxiliary heat less efficient?

Discussion in 'The Okie Corral' started by Harper, Feb 16, 2013.

  1. Harper

    Harper

    Messages:
    2,610
    Likes Received:
    15
    Joined:
    Aug 10, 2010
    Why is auxiliary heat considered less efficient? Usually when we hear about efficiency it has to do with the amount of energy not lost to heat. So in this case the aux heater must be doing more work for the amount of energy used, but wouldn't that technically be more efficient?
     
  2. kf4zra

    kf4zra I miss ya Murph

    Messages:
    1,872
    Likes Received:
    56
    Joined:
    Aug 15, 2002
    Location:
    Tampa, FL
    if you are talking about a heat pump, then my understanding of it goes like this.

    The heating side of the heat pump basically acts like an AC system in reverse. It takes the heat from the outside air and transfers it to the inside air by means of a change from liquid to gas of a refrigerant.

    When the temperature gets too cold to make this work well, then you select aux heat to turn on electric coils. The coils work based on resistance, which is inherently inefficient energy wise.

    I am sure others can go into it more in depth, thats just the 2 second version of it.
     

  3. Harper

    Harper

    Messages:
    2,610
    Likes Received:
    15
    Joined:
    Aug 10, 2010
    Sorry, yes I'm talking about a heat pump.
     
  4. RenoF250

    RenoF250

    Messages:
    12,214
    Likes Received:
    9,068
    Joined:
    Feb 23, 2008
    This is correct. It is more efficient to move the heat from outside to inside than make heat from electricity.
     
  5. Harper

    Harper

    Messages:
    2,610
    Likes Received:
    15
    Joined:
    Aug 10, 2010
    I guess I didn't realize the heat pump actually works like the A/C in reverse.
     
  6. jdeere_man

    jdeere_man CLM

    Messages:
    2,755
    Likes Received:
    130
    Joined:
    Feb 25, 2007
    Location:
    MO
    right and "auxiliary heat" is just the same as using electric heat or an electric furnace because that's what it is.

    That is a typical situation. There is a possibility you could have an alternative form of "alternative heat" as a backup to a heat pump or geothermal system though.
     
    Last edited: Feb 17, 2013
  7. HarleyGuy

    HarleyGuy

    Messages:
    3,577
    Likes Received:
    285
    Joined:
    Mar 29, 2008
    Energy costs can vary in different parts of the country and anyone considering any heating and/or cooling system should do a lot of checking prior to making such a large investment.

    I have no experience with a heat pump but several years ago, I had a geothermal system installed (which I believe is an underground system that is similar in operation to a heat pump). I did so due to the rising cost of LP (liquid propane) gas, and for Michigan, geothermal is the most efficient way to heat and cool a home even though an auxiliary heat source may be needed in extremely cold weather.
    I have what's called a "split system" and I can use my LP as the auxiliary heat if needed but I will be replacing the LP with natural gas this summer.

    It's always nice to have some auxiliary heat in the event of a power outage and everyone should be prepared just in case.
     
  8. podwich

    podwich

    Messages:
    4,807
    Likes Received:
    577
    Joined:
    Sep 7, 2000
    Location:
    MI
    Electric heat is extremely efficient at converting the source energy into the used heat. However, the cost of that energy isn't all that cheap.

    A heat pump uses electricity to transfer heat from the ground and into your house. Thus, you're only paying to move heat, not make it.

    So, instead of looking at efficiency as the percent of energy converted into heat, look at it as the cost you pay to heat your house-- in the case of the heat pump, the heat is free. You just have to move it.
     
  9. jdeere_man

    jdeere_man CLM

    Messages:
    2,755
    Likes Received:
    130
    Joined:
    Feb 25, 2007
    Location:
    MO
    We also have geothermal loop. In our case we have auxiliary electric heat because it was convient I guess. Never have we switched to aux heat. If we had a heatpump we prob would though. I'm not a fan of heat pumps, but I like the geothermal. If we ever loose grid power we have enough generator to cover the geo system.
     
  10. Harper

    Harper

    Messages:
    2,610
    Likes Received:
    15
    Joined:
    Aug 10, 2010
    I got that once I realized what a heat pump actually was.
     
  11. jdeere_man

    jdeere_man CLM

    Messages:
    2,755
    Likes Received:
    130
    Joined:
    Feb 25, 2007
    Location:
    MO
    when most people refer to a heat pump they think of an "air source heat pump" from a technical standpoint that of course isn't the only form, but it is the most common in terms of reference to "heat pump" I think.

    I've always called "ground source heat pumps" geothermal systems, not even calling them heat pumps, which they technically are.

    We have geothermal here, but a lot of people (city dwellers) dont have room for ground loops unless they're lucky enough to have the excess property
     
  12. JBG30

    JBG30

    Messages:
    830
    Likes Received:
    8
    Joined:
    Apr 16, 2001
    Location:
    Pittsburgh, PA
    In an air to air heat pump you are taking the heat from outside and transferring it inside with the added heat from compression.

    Electric heat is 100% efficient in theory. Every watt gives you 3.41 btu's. However, when running electric heat you mess with the heat pumps COP (coefficient of performance). Simply put, the heating output divided by the electrical input.

    Basically the electric heat has a COP of 1. The compressor may have a COP of 3, or 3 times the heat for the money. Add them together, and the returns diminish for the price.