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  1. #1
    Join Date
    Oct 2019
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    7
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    2 stage heating / variable speed blower

    Hello,

    I recently had a 2 stage heating/variable speed ECM blower furnace installed - G8MVL0701716B, along with a new outdoor A/C unit. With this setup, I'm using a Nest gen 3 learning thermostat.

    I'm the curious type and wondered how the variable speed blower functions. Being unsure if it's control board or thermostat driven, I jumped in on some research and found a lot of info, but I'm not 100% sure I currently am setup to use this system to its greatest potential.

    Can anyone confirm that short of using an Observer thermostat, the variable speed blower motor is going to be driven by the furnace's control board and NOT the Nest thermostat? I don't think the Nest or any 3rd party is capable of "intelligently" controlling the air speed.

    Also, this is supposedly a 2-stage heating furnace. I checked just now in my Nest app to see how the wiring is currently setup (I originally installed this thermostat on my previous 1-stage, 1 speed furnace), and only the W wire is connected for heat; the W1/aux is not connected to anything. Shouldn't this be connected to make use of the 2-stage heating functionality? I live in a generally warm climate with fairly mild, but generally cold, winters. I think I'd get a lot of benefit out of the 2-stage heating this system was supposedly designed for.

    I can contact the original installer, but I wanted to check with you guys first before I bother them with my amateur HVAC ambitions.

    Thanks

  2. #2
    Join Date
    Jan 2004
    Location
    PA
    Posts
    78,011
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    Always better comfort if the thermostat is controlling staging.
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  3. #3
    Join Date
    Oct 2019
    Posts
    7
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    Thread Starter
    Are you saying I should get an Observer, or that I should hook that W2 wire up?

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
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    Doubt you really need the Observer, but myself I would set it up to use the thermostat to control staging .
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  5. #5
    Join Date
    Oct 2019
    Posts
    7
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    Thread Starter
    Simple as hooking the W2 wire up on the nest and on the control board? Do you know if any jumper settings need to be altered on that furnace?

  6. #6
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
    Posts
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    I would suggest throwing the Nest out, it has a well earned reputation of causing erratic operation and causing failure to electrical components, like the control board. There are tstats out there that do all the things the Nest does and more and wont break your system. Your right about needing the observer to control fan on speed and for dehumidification mode. Your installers either hooked the furnace up as single stage or it's on a timer that will go to high stage after X amount of run time in low stage.

  7. #7
    Join Date
    Oct 2019
    Posts
    7
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    Thread Starter
    So I’m noticing that on here, about the Nest. After more research, it looks like those issues are attributable to systems that aren’t using a C wire. Mine is. So it doesn’t need to ‘steal’ voltage to get its job done.

    My wife has asthma and is constantly complaining about the HVAC blowing too hard (the old one). When I bought this variable speed one, I was under the impression that:

    A) the fan would run slower, more often
    B) the above causing additional filtration through the 5” filter

    Both of these things hopefully leading to an improvement in air quality, and thus her asthma.

    I’m not sure I have what I need to accomplish this. Sounds like the system may be programmed to ramp up but that’s about it? I’d need a communicating stat to achieve the true comfort of the variable speed fan?

  8. #8
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
    Posts
    1,351
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    I think most of the Nests I've disposed of had a C wire as well, it's just a crap design with really good PR. A 2 stage furnace in low heat is putting out 65% of the btu capacity and airflow of high stage heat so it will run longer and leaving the fan switch to on will run it at half the A/C fan speed, constantly stirring the air and filtering it. Right now, my guess would be that it's only running in high stage heat all the time, as that's what I see installers do around here, even when they have enough wires at the tstat. Blowing to hard is a common complaint on oversized equipment connected to undersized ducting, were improvements made to the ducting or was the system capacity reduced?


    .

  9. #9
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    24,367
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  10. #10
    Join Date
    Oct 2019
    Posts
    7
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    Thread Starter
    Nothing changed with the ducting. I believe they just swapped it out with similar sized equipment, but used a variable speed furnace instead of single speed. And apparently didn’t hook it up to use the lower stage heat.

  11. #11
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    2,133
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    If you are concerned with controlling fan speed for circulation, as well as, enhanced dehumidification, the Observer is the best option for that furnace. As mentioned you at least need the 2nd stage connected to the thermostat so heat staging is controlled by temperature.
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  12. #12
    Join Date
    Aug 2002
    Posts
    2,422
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    Ask for the ION. It is the same as the infinity/evolution.

    It also enhances the cooling functions more than your nest could even think about doing. Not to mention the better staging and enhanced diagnostics for the furnace.

    And yes the ION is WiFi capable.

  13. #13
    Join Date
    Oct 2019
    Posts
    7
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    Thread Starter
    Thank you for your responses everyone. I’m in contact with the installer now.

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