Does a programmable thermostat for an in-floor electric radiant heat system add efficiency, or is it faux efficiency?
My electrician installed in-floor electric heat in a second floor bathroom remodel I recently completed, and he used a non-programmable therm. I asked him to change it, and he pushed back that there is little efficiency gain because the thermal mass of the mud bed and tile create a long cycle time to raise the temperature. Better to leave the temperature set, and have short cycles throughout the day to maintain it, he argued. He admitted this was merely his opinion.
I have looked for studies on this and found little information so far.
The particulars of this project are that the home was built in the 20's, but it has blown-in cellulose (probably R-10) throughout the house and approx. R-40 in the attic, which is above the bathroom. In the bathroom, I removed the plaster, cleared out the cellulose to below the floor joists, then used closed-cell spray foam in the bathroom to achieve R-20 in the walls and rim cavities (balloon framing allowed access). The house's primary heat is radiant, with the bathroom above the kitchen. There is no radiator in the bathroom, but since this is Minneapolis, I installed an electric baseboard heater on a programmable thermostat in the room-- as a fail safe. The homeowners set their home to 65 while away or asleep, and 70 while active in the house.
My opinion is that the floor only needs to cycle up 10-15 degrees, and that through experimentation, the homeowners can start that cycle early enough in the morning to have desired temperature when they start to use the room. I also think the floor could cycle off in the middle of the evening and retain a comfortable temperature until past bedtime.
The in-floor electric is supplemental and primarily about comfort, of course, but I think it can still be operated in a more efficient manner through programming.
I'd love some data that supports or refutes my thinking.