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  1. #1
    Join Date
    Dec 2006
    Rochester, NY


    I recently had a new furnace installed in my house in Western NY State. The furnace is an Amana AMV90704, a 96% efficiency furnace with variable speed ECM blower. My wife and I are very happy with the choice and we look forward to saving on our utility bills versus the 20 year old 80% efficiency furnace it replaced. I have a question regarding my new furnace and using it with an auto setback thermostat.

    We had a couple of contractors in to look over what we had, see the furnaces that they had to offer and so on, and we heard a couple of different opinions regarding whether or not to actually use the auto setback function on the thermostat with the variable speed ECM blower condensing furnace.

    One contractor told us that this furnace would use less electric/gas in the long run if we left the thermostat set at a constant temperature, so that it would run all day at, what he said would be, about 40% capacity. He suggested that it would use less fuel this way as compared with turning the heat down, say 5 degrees, overnight and while we were at work during the day, and forcing the furnace to fire at full capacity in order to heat the house back up again at the end of that cycle.

    Another contractor we asked, and everything that I've found on the internet, indicated that we'd save more money by utilizing the auto setback function of the thermostat, turning the heat down 5 degrees while we're asleep, and while we are at work.

    I would love to hear what you know on this topic: whether we'll pay less in utilies (gas & electric) by keeping the temperature steady, or by turning the heat down 5 degrees at night. If you are aware of any research that compares the energy use of these two scenarios, please direct me to where we could read up on the topic, particularly if the conclusion is the first option (keeping the temperature steady). If you need more specifics on the furnace that I'm referring to, please let me know, and I'll see what I can come up with.

    Thanks in advance for your help. I look forward to hearing your responses.

  2. #2
    Join Date
    May 2006
    east central indiana
    I would use the setback.

  3. #3
    Join Date
    Jul 2000
    Northern Wisconsin
    Plug your numbers into this calculator and find out.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    Mar 2005
    burlington county n.j.
    i would use the setback, i like sleeping in a colder area anyway. every house is different depending on insulation, ductwork, furniture layout etc. try it both ways and see what works for you.

  5. #5
    8-10F degrees setback at work and overnight for max savings...

    like t527ed said, try both and see what you like.

  6. #6
    Join Date
    Feb 2006
    DC Metro
    For heat pump set back is ideal for temperature above 37 degree. What i have noticed with my heat pump(XL14i VS) is that you cannot recover from even a one degree set back, without using Aux heat at temperature below 35 degree. My advise only set back at temperature above 40 degree

  7. #7
    Join Date
    Jan 2003
    City, he doesnt have a heat pump.

    I would use the set-back. Staging does not effect the effciecy of the furnace.

  8. #8
    Join Date
    Oct 2004
    I would also use the set back.

  9. #9
    Join Date
    Nov 2006
    I agree...Use the setback.

    What would make it even better is if your thermostat has an Intelligent Recovery feature that raises the temperature a little at a time so that the second stage doesn't have to fire. That way, everything gets heated evenly instead of just the actual air temperature rising rapidly and possibly creating a need for the funace to cycle continuously.


  10. #10
    Interesting question.
    If you have a 1 stage heat 1 stage cool programable tstat you could be in trouble using the set back. With 1 stage heat your furnace will operate on low fire (1st stage) for 10-15 minutes before it shifts to high fire (2nd stage). During recovery from set back you may be uncomfortable until you reach set point temperature or the furnace shifts to high fire.
    If you have a 2 stage heat 1 stage cool programable tstat the recovery time should be much shorter as the 2nd stage heat should fire almost immediately.
    I like to sleep in a cool house so I'd use the programable tstat but it's got to be the right one.

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