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  1. #14
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    Jan 2004
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    I think the only time you would have a condensation problem in first stage and not second stage is.
    A. You pulled out a 120,000 and replaced it with a 60,000, and didn't set it up for proper temp rise. (of course applies to situation that its not set up right)
    B. The customer sets the stat to 50 when they go to work.

    JMO
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  2. #15
    Join Date
    Aug 2003
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    466
    Quote Originally Posted by BaldLoonie View Post
    My 2 stage has run on low 98% of the time due to being oversized. I have no condensation issues in the heat exchanger nor the flue pipe. Not finding issues on our customers units who are more appropriately installed.

    The Goodman/Amana units are the only 2 stage units on the market that cannot have a 2 stage stat. I agree that an algorithm beats a fixed timer but still, the unit will time to high in 16 minutes eliminating the best feature of a 2+ stage furnace, long run periods on low in bitter weather. If they are doing this to keep 1st stage run cycles short intentionally then why does the variable speed models encourage the purchase of a 2 stage stat?
    I really thought that I had been told that the Carrier familiy of furnaces had the same type of control available for some of their two stage furnaces. It seems odd that Goodman Manufacturing would have an exclusive control feature. Goodman usually follows trend rather then being the innovator of technology.

  3. #16
    Join Date
    Aug 2003
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    A condensation issue would only occur under certain conditions. Obvously there would need to be moisture, which LP gas usage would provide in the fuel itself. Corrosives in the combustion air would also promote condensate issues. The industry has been seeing burnouts on the first bend of heat exchangers which can be attributed to moisture causing hot spots during initial low fire start ups.

    With everything else aside, having the control board determine the furnaces function based on heat loss calculations rather then responding only to stimuli local to the thermostat will be better for many home heating situations. Just think how well the Rheem controls do for comfort. Rheem has been an innovator of multistaged furnaces having had a two stage natural draft furnace available in the 1970s.

  4. #17
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    The Rheem mod uses a varying DC control voltage through the stats V terminal.

    The York mod is strictly throught the board.
    using both time and algorythm based on last heat calls, and current run time.
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  5. #18
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    Aug 2003
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    Quote Originally Posted by beenthere View Post
    The Rheem mod uses a varying DC control voltage through the stats V terminal.
    Which is still gathering information accumulated over a period of time, which is why this "V" terminal cannot be interrupted. This is why a standard zoning system cannot be used with the Rheem mod furnace, or at least didn't used to be able to be used and still keep the modulating feature.

  6. #19
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    Baldie can correct me if I'm wrong.
    But if the voltage from the V terminal in teh mod stat increases. The furnace firing rate increases, reguardless of how long its been running.
    The stat increases or decreases the voltage based on room temp, not run time.
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  7. #20
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    Quote Originally Posted by beenthere View Post
    Baldie can correct me if I'm wrong.
    But if the voltage from the V terminal in teh mod stat increases. The furnace firing rate increases, reguardless of how long its been running.
    The stat increases or decreases the voltage based on room temp, not run time.
    I'll need to go back and reread my literature on the Enerstat setup for this system then. It just seems that if the stat only reacts to localized temperature, there would be no need for continuous power to be supplied to the "V" terminal. Originally this control function was referred to as using fuzzy logic which the way I am reading it functions the same as algorythmic controls.

  8. #21
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    Would fuzzy logic be needed to determine how much to increase or decrease input rate by how quick the temp is rising, or how much temp is being lost at current firing rate.

    So that when it is gaining, it doesn't prematurely lower firing rate and lose temp.
    Or raise firing rate too fast and shut off too quicj defeating the purpose of mod.
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  9. #22
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    May 2000
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    Indianapolis, IN, USA
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    Quote Originally Posted by everythingair View Post
    I really thought that I had been told that the Carrier familiy of furnaces had the same type of control available for some of their two stage furnaces. It seems odd that Goodman Manufacturing would have an exclusive control feature. Goodman usually follows trend rather then being the innovator of technology.
    Carrier has had this technology for YEARS. With one exception that I've found, they have always allowed the use of a 2 stage stat as well. Goodman on the H models doesn't.

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