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  1. #14
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    Apr 2004
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    Remember burner efficiency is not the issue, its input versus output and ultimately there is very little difference. The 2 stage, as we all agree, is for comfort, and we would then have to ask what value you put on additional comfort.

  2. #15
    Join Date
    Jul 2002
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    962
    They will both burn the same amount of fuel.

    Now, if you compare a 90 two-stage and a 90 single stage, which one is more effient?

  3. #16
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    Jul 2002
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    I agree that the two stage is for comfort, since the manufacturers only rate the two stage, one or two points higher than single stage.

  4. #17
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    Nov 2004
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    I think 2 stage is more efficient.(or i wouldnt butt in here)
    Longer run times throughout the entire heating season ,and not just on design days, are one reason.

    Or am I thinking weird?

  5. #18
    Join Date
    Apr 2004
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    Yes, you are thinking weird, that would be a comfort issue not an efficiency thing. Your system, regardless of stage will provide the correct amount of heat by burning the same amount of gas over the course of time. Its a matter of burning a candle at one end or both, either way the same amount of wax gets burnt when the candle is gone.

    Now, one could argue that longer run times require the blower and inducer to operate more and therefore a slight cost increase for running motors could be considered. Again the difference here is in comfort or ability to stay at set point versus cycling using and having swings between a call for heat and the end of a cycle.

  6. #19
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    Nov 2004
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    /

    [Edited by jacob perkins on 10-19-2005 at 09:46 PM]

  7. #20
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    Nov 2004
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    2,927
    Originally posted by docholiday
    Again the difference here is in comfort or ability to stay at set point versus cycling using and having swings between a call for heat and the end of a cycle.
    that was my point,cycling is less efficient.
    ignoring electric.

    in a region like new mexico ,texas ,or tennessee where winter temps are wildly unpredictable,with the issue of cycling and (oversizing for a few days of the year)the two stage is more efficient for the reason you stated.

  8. #21
    Join Date
    Feb 2005
    Posts
    655

    Different Opinions

    If you think both 90% units would consume the same amount of natural gas (single stage and two stage)in the same season even if the two stage ran 80% of the time on low fire,
    than using that analogy the 35/50 input would consume
    the same amount of fuel to heat the home for a season as
    a 75,000 btu 90% single stage unit right? "WRONG"

  9. #22
    Join Date
    Jul 2004
    Posts
    322
    I like the 2 stage because it is much quieter on low stage, and runs on that stage most of the time.

  10. #23
    Join Date
    Apr 2002
    Posts
    11,808
    The inducers are not two speed?

    Longer run times would save energy, each ignition cycle wastes energy as it warms up to steady state.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  11. #24
    Join Date
    Mar 2004
    Posts
    1,042
    Originally posted by Carnak
    The inducers are not two speed?

    Longer run times would save energy, each ignition cycle wastes energy as it warms up to steady state.
    All that stuff is already considered in AFUE. It is a "big picture" rating.

  12. #25
    Join Date
    Mar 2001
    Posts
    715
    The Inducer fans ARE two speed, or at least the one on my Lennox furnace is. I can tell you that comfort is a major reason to go with two stage units. I have had mine for several heating seasons and am very happy with it. Insist on a two stage thermostat, don't let someone tell you the built in timer in the furnace will take the place of a good two stage stat!!

  13. #26
    Join Date
    Jul 2002
    Posts
    962

    Re: Different Opinions

    Originally posted by wallynut
    If you think both 90% units would consume the same amount of natural gas (single stage and two stage)in the same season even if the two stage ran 80% of the time on low fire,
    than using that analogy the 35/50 input would consume
    the same amount of fuel to heat the home for a season as
    a 75,000 btu 90% single stage unit right? "WRONG"
    Is the 75,000 over sized or undersized? Why compare such an un-realistic situation?

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