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High-efficiency furnace modes

Bryan56 | Posted in General Questions on

This might not be the best forum for this question but here it goes…..I just got a high efficiency dual stage furnace installed (LENNOX EL296E Series Dual-Stage 96% Efficient Gas Furnace). I don’t think the blower is variable but comes with a consistent torque motor. It also came with a Nest thermostat. My questions is how does the system know what stage the furnace should run in and what speed the blower should be at? Does the furnace make this determination or is the Nest thermostat telling it what mode to operate in?

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Replies

  1. Reid Baldwin | | #1

    There is probably a setting for the furnace that indicates whether it is hooked up to a single stage thermostat or a two stage thermostat. If the setting is set to two stage thermostat, the furnace will let the thermostat decide whether to run on high stage or low stage. If the setting is set to single stage thermostat, the furnace will use its own algorithm. Most commonly, the furnace will run for 10-12 minutes on low stage and the switch to high stage for the remainder of the call for heat. The thermostat may also have a setting to indicate whether the furnace is single stage or two stage. If you are counting on the thermostat to decide staging, it needs to be set to two stage.

    You didn't mention multiple zones. If you have multiple zones, then there is a zone controller between your multiple thermostats and the furnace. In that case, the staging logic could be in the furnace or the zone controller.

  2. Bryan56 | | #2

    Thanks for the quick response. The furnace is hooked to a 3rd gen Nest thermostat. I just checked the wiring and I see W1(heat), G(fan), C(common) and Rh(Power). The Nest website says there should be a W2 for second stage heat. Does this sound right?

    This is only for 1 zone.

  3. Jamie B | | #3

    I am not even close to an HVAC tech.

    Generally speaking from me looking at lennox wiring diagrams:
    W1 is stage one heat, W2 is stage two heat.
    Y1 is stage one cool, Y2 is stage two cool.

    The thermostat makes the determination of stage 1 or 2 blower speeds. And energizes the appropriate wire above to the furnace to tell it which speed to use.

    I beleive the furnace will have Dip switches that will change the timing parameters of when stage 1 and 2 is called for. You can read these in the EL296E installation manual.

  4. Bryan56 | | #4

    Thank you. I was able to pull up the install manual and check the specs. Looks like everything is setup correctly but wont be able to test until the cold weather starts.

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