We have 2 single stage AC/NG gas furnaces serving a common area. We would like to set them up for 2 stage operation on a common programable smart thermostat. Should I combine the R and C wire from each air handler and connect them together at the R and C terminal on the thermostat? Are there phasing or capacity considerations? Both units get power from the same circuit breaker.

  • Why do you have two furnaces serving the same area? Can you post the make and model of the thermostat and of the furnaces involved? – ThreePhaseEel Nov 10 '19 at 23:31

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