A:Answer No way for me to know for sure, of course, but given that you already have three thermostats, I suspect they connect to a zone control board in your HVAC system. That board, then, likely controls which ducts air can and cannot move through, and also determines fan state and calls for heating or cooling. IF that is true, your zone board needs input from each of your thermostats. One Ecobee, in that case, will not replace all three thermostats. The Ecobee remote sensors provide for a sort of "virtual zoning" and do not directly integrate with a hard-wired zoned system you might have installed. For full effect, you would have to replace all three thermostats with an Ecobee.
