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  1. #1
    Join Date
    May 2007
    Posts
    42

    Question Single Stage vs. 2 Stage T-stat

    Hello, all. I am a newbie here, but I have been reading posts for a year or so. Excellent site, very helpful. I just installed a Bryant Evolution Plus furnace
    (80%, 2 stage, VS fan), a Bryant single stage A/C condenser, and a W-R single stage touchscreen t-stat. I'm very happy with the install, good installer (Factory Certified, NATE, etc.). I read on here that a 2 stage furnace should always have a 2 stage t-stat. I spec'd a 2 stage t-stat for this job, but the installer vehemently insisted on a single stage t-stat. He said that the Evolution has its own board that controls the 2 stage logic/algorithms, etc. so there is no need for the t-stat to do that with a 2 stage t-stat, and that if I had a cheaper unit without the board, only then would I need a 2 stage t-stat the run the logic/algorithms, etc. He also mentioned that the condenser was only a single stage. Is the installer correct? If not, was he trying to keep the job within budget (is a 2 stage t-stat much more $ than a single stage t-stat?), or was he trying to avoid pulling new wires (the wire path in my house to the t-stat is a bit convoluted, perhaps the installer recognized this and was trying to avoid more labor cost on the budget? Does a 2 stage t-stat require more wires than what was on the 1960's vintage system that was replaced?) I'm trying to decide if I should go back to the installer now, while the system is very new, and request a swap-out to a 2 stage t-stat. The posts here say that you get better "comfort" with a 2 stage t-stat. My system seems very comfortable so far. "Comfort" is a bit vague. What specifically am I missing without a 2 stage t-stat? Your thoughts, input, and opinions would be most appreciated and thanks for reading!

  2. #2
    Join Date
    Aug 2004
    Location
    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia
    Posts
    318
    I am not familiar with that particular furnace. As a rule though, yes a 2 stage stat would be your better bet. The furnace is manufactured to provide multiple installation variables. It (the furnace board) doesn't know if you have a multiple zoned system, air flow characteristics of the stat location, etc. Unless the literature with the furnace specifically requires a single stage stat, I'd use one. And yes, there needs to be another wire for the 2 stages of heat.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  3. #3
    Join Date
    May 2007
    Posts
    42
    Hi, Ira, thanks for the response. Since the condenser is still only single stage, and if I usually run heating on "Auto" rather than on the "Fan On" setting, would a 2 stage t-stat really be cost-effective in terms of the cost to upgrade to the new t-stat, and the labor cost for pulling the new wire? Or am I really running a "tweener" system that is functioning more like a single stage system, so that a single stage t-stat isn't so bad? Thanks! mrbee

  4. #4
    Join Date
    Jan 2006
    Location
    indy
    Posts
    56
    A 2 stage t-stat will help with heating will call for 2nd stage quicker than the control board on furnace. you need 2 stage heat 1 stage cool you will save money.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,761
    The 2 stage stat will still provide better comfort then the boards logic.

    As far as pulling more wires, he can use the Honeywell IAQ, it only needs 3 wires to the stat. It is more expensive, but saves teh labor of pulling new stat wires.


    The furnace board will force second stage after the furnace runs for so long.
    The stat will keep it in first stage as long as the temp is not dropping.
    If it really didn't work better with a 2 stage stat, why would it have terminals for a 2 stage heat stat.
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  6. #6
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    Quote Originally Posted by mrbee View Post
    I usually run heating on "Auto" rather than on the "Fan On" setting, would a 2 stage t-stat really be cost-effective in terms of the cost to upgrade to the new t-stat, and the labor cost for pulling the new wire?
    Since you got a nice variable speed system, I'd suggest turning on the fan in the winter to move the air. It'll make the house more even in temps.

    I'd go and put in the IAQ t-stat, they only need 3 wires, where most other two stage t-stat will need 5 or 6 wires.

  7. #7
    Join Date
    May 2007
    Posts
    42
    Hello, all, and thank you for all of the helpful and informative responses. You are all true professionals. I will study the IAQ unit and post how this issue turns out and resolves itself. A great weekend to all! mrbee

  8. #8
    Join Date
    Jan 2007
    Posts
    5

    Single Stage vs. 2 Stage T-stat

    This subject turns up in this group every few days. Why? Do the HVAC professionals have something against the manufacturers who design and build 2 stage furnaces. For me, as a consumer, if the manufacturer recommends a 2 stage thermostat, it should be installed. I had a Trane XV90 installed last month and frankly had to argue with the installer to have a 2 stage T installed. He thinks I'm crazy, spending extra monies for the 2 stage T. For 2 weeks before he installed the 2 stage T, the furnace ran on the timer and it ran often. Ten minutes on low then on high. Since installing the 2 stage thermostat, I find the furnace runs on low the majority of time and the temperature on the 'stat never varies. Simply put, would all you HVAC experts install what the manufacturers call for. I'm sure that most consumers who order a 2 stage furnace, would absorb the extra cost for the 2 stage stat.

  9. #9
    Join Date
    May 2007
    Posts
    42
    Cmore, I went around and around the horn with the installer on this issue while the install was in progress. It started to get a bit ugly and I backed off to the 1 stage t-stat. I couldn't figure out why there was an issue here, I thought maybe it was me being picky or something, it's been bothering me ever since the install, so I decided to post it up here. It looks like I have only 3 wires, previous posts indicated the IAQ only needs 3 wires. I have a W-R now, it's fine (except for 1 stage), does W-R make a 2 stage 3 wire t-stat like the IAQ? Again, thanks to all who responded.

  10. #10
    Join Date
    May 2007
    Posts
    42
    Hello all, again. I've been doing some homework (nothing else to do- home ill for 1 week!!). The current single stage t-stat is a W-R 90 Series #1F97-1271.
    The 2 stage W-R t-stat I could switch to (it might be easier for the installer to swap me out to another W-R unit instead of a different brand i.e. Honeywell IAQ) is a W-R 90 Series #1F95-1277. Does this 2 stage W-R require more wire(s) to be pulled, or can it use the same amount of wires as the single stage W-R?? I tried to figure this out on the manufacturer's pdf wiring diagrams, but this is way beyond my expertise, the diagrams look like a foreign language to me and it's not just because I am ill! Your input and thoughts would be most appreciated once again, and many thanks

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,761
    It will need more wires then the IAQ.
    Currently, teh IAQ is the only stat that only needs 3 wires to the wall stat and can still control 2 stage equipment.
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  12. #12
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    White Rodger is going to need 5 or 7 wires.

    Power
    Heat 1
    Heat 2
    Cool
    Fan
    Common (If not used, then battery must be used)
    Dehumid (I am not sure if this t-stat has it or not)

    IAQ

    COM 1
    COM 2
    COM 3


    3 wires goes down to an Equipment Interface Module, then it ties to the furnace.



  13. #13
    Join Date
    May 2007
    Posts
    42
    Thanks for the wiring info, this answers many questions I had!

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