I have another identical thermostat in the bedroom that controls my heat pump (not the gas furnace) and noted that the white wire is also wired to the GH terminal (Fan Hi) on the thermostat. There is a second red wire at this location that is wired to the W terminal (furnace) which I'm assuming is the heat pump. There is no second green wire or gray wire at this location. In both locations it looks like the white wire is plumbed to the GH terminal.

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