A:Answer You would need one thermostat per zone. As far as I know, none of the smart thermostats support multiple zones off of the remote sensors. There's no reason they can't, I just don't know of any that support this yet. I had to replace both of mine. Typically you have a thermostat per zone, but you also typically only have one zone per floor, so you might check if your current setup is 2 or three zone. The T9 has some additional limitations that the Ecobee doesn't. I decided to go with the Ecobee because of those features. The Verge gives a good review of the T9 and it's pros/cons.