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  1. #1
    Join Date
    Jan 2001
    Posts
    201

    2 stage or single stage heat exchanger

    Where do you draw the line in installing/recommending the 2 stage? Customer request to save money? Old uninsulated home versus new tighter home?

    Or because of their efficiency you recommend all of the time?

  2. #2
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,222
    Perhaps in cold climates where the system runs 6+ months per year would be the best for 2 stage. Otherwise just properly size a single stage. 2 stage is for comfort, not energy savings.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,109
    What he said. They are for comfort. Some would say they are less efficient on low. Certainly something to offer every customer along with a good 2 stage stat. And then if they choose single stage, at least they had the choice. Usually if you give a good, better, best, the average person tends to choose in the middle. If you offer 2 choices, often they choose the lower.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,935
    They make 2 stage 80% furnaces. I offer them for comfort, not for savings.
    Contractor locator map

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    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Aug 2008
    Posts
    416
    I have a question??

    OP specifically said 2 stage heat EXCHANGER (as in high efficiency furnace) and then asks about efficiency.

    The * answers seem to be about 2-stage heat (i.e. low fire and high fire)

    Are these the same???

    I thought high EFFICIENCY furnaces have a secondary heat exchanger, but they are not always 2 stage heat???

    Clarification appreciated.

  6. #6
    Join Date
    May 2004
    Posts
    534
    Correct. You can have a single stage or a dual stage furnace.

    The single burns at the furnace rating. i.e. 80,000 BTU's
    The dual stage furnace burns on low fire, say 36,000 BTU's and high fire 80,000 BTUs

    It requires different t-stat too, as when the temp is less then 1 of the t-stat setting the furnace will burn in 2nd stage or high fire.

    They might talk about having a secondary stainless steel heat exchanger in the high efficiency furnaces, but that just pulls that extra 10%+ heat out of the flue gases to help get a higher AFUE rating on the furnace.

    I always recommend a 90+ single stage furnace, when cost is a big factor. If comfort is a bigger issue. i.e they complain about the previous unit, then getting 2 stage with a variable speed blower is a better option.

    Note: They make 2 stage furnaces without the variable speed motor, but the variable speed motor saves on energy and provides better comfort. i.e you will feel more comfortable with the system going on and off all day long.

  7. #7
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,015
    Quote Originally Posted by r-290 View Post

    It requires different t-stat too, as when the temp is less then 1 of the t-stat setting the furnace will burn in 2nd stage or high fire.
    Agreed, except for that part.

    Not all 2 stage furnaces REQUIRE a new stat, all though it is highly suggested.

    Without a 2-stage stat, it's based on previous runtimes, instead of actual heat needed in the home.
    Or, a simple time delay.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  8. #8
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,109
    No they don't require a 2 stage stat. But if comfort is desired they should have one. Timers, even those based on past cycles, won't allow long run times on gentle low fire. They time up, shut down, start up, time up, shut down..... I'm getting tired of typing but that's what they do! 2 stage stats don't.

  9. #9
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,222
    If you aren't going to spring for the 2 stage stat, why spring for a 2 stage furnace?

  10. #10
    Join Date
    May 2004
    Posts
    534
    all true.

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