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Hot and cold at the same time?

Switching my Goodman GPH14H from a single zone to a 2 zone with NEST thermostats, each activating its own damper. I would assume I could connect both Y's together and both W's together and feed that to the Y and W terminal of the Goodman.
My question: what happens if one thermostat tells the system to cool and the other tells the system to heat?
I assume the system would default to a priority heat mode or do nothing. Anybody that could confirm this?

I guess that the right answer is to use a 2 zone relay station. I just don't like to complicate the system with a zone relay station. I don't care what the Goodman does as long as it doesn't go up in smoke or requires a manual reset.
Any help would be highly appreciated.


  • unclejohn
    unclejohn Member Posts: 1,833
    You have a heat pump. Do you have any back up heat.
  • Jamie Hall
    Jamie Hall Member Posts: 23,430
    The most likely result is that something will fry. You might get lucky and have it be a fuse. Might be one or the other or both of the Nests. Might be something else. Without looking in some detail at the actual wiring of the various units -- internal wiring -- one couldn't say.

    I'd use a relay to isolate things.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT Member Posts: 5,861
    edited December 2017
    With the dampers, you need to install a zone damper control board. I would also put in a barometric bypass. In the old days there was a master thermostat and slave thermostats so you couldn't have one in heat and one in cool. The master controlled the mode. Maybe we were more dumberer then.
    Or you could ditch everything and put in a Mitsubishi City Multi system. You can run heat and cool to different zones at the same time. They're major bucks though.
    EBEBRATT-Ed Member Posts: 15,614
    In short you can't do what your trying to do without more hardware and more wiring. Options are:

    Keep it 1 zone and balance it

    Install two dampers with a zone panel and a bypass damper as @HVACNUT correctly mentioned
  • ratio
    ratio Member Posts: 3,649
    There are a number of residential zoning solutions available, we typically use a Honeywell TrueZONE panel. You really should install a bypass damper, as noted above.

    Be aware that if the system isn't performing good now, it probably isn't going to perform much (any?) better after zoning. Sizing, both the unit & the ductwork, is critical for good operation, both single zone and multi-zone. The odds of an incorrectly sized single zone system just happening to be sized correctly for multi-zone operation is ...well, you spends your money and you takes your chances. :disappointed: