I have a standard gas furnace, but recently installed an electric radiant floor in one room. I have a transformer at the electric floor and a regular low voltage thermostat wire to my Nest thermostat.
I can wire the floor wire into the Nest as an 'auxilary' heat, and specify that it is electric radiant, and both heat sources work as expected. However, what I really want is for the floor to kick-in when not at a higher temperature than the gas furnace does, so the floor can be warm even if the gas furnace is not required to heat above its separate temperature.
I believe this is the entire purpose of a heat-pump (to turn on and heat at moderately low outside temperatures, but use additional heat sources when required). The Nest supports wiring for heat-pumps. What if I just wired the electric floor as a heat-pump and told the Nest that's what it was? Are the signaling voltages any different?