We have been shopping for a new thermostat that will integrate with SmartThings, but continue to use the efficiencies of our Trance XV90 furnace. The furnace is a two-stage, variable speed blower (Single stage cooling). I contacted EcoBee and they indicated their thermostats will only act as an off/on sensor, so the variable speed will not work.
For some reason I thought the speed was determined by the furnace, but would like to hear other peoples recommendations or experiences.