What thermostats do people recommend for radiant installations in low energy houses for both low mass and medium mass floors?

This house will have electric radiant heat in 2" slab in the bathrooms and entry. The rest of the house is a low mass hydronic 5/8" PAP in heat transfer plates with plywood sleepers under 1/2" engineered hardwood. The basement is baseboard heating.

The current plan is to use a electric hot water tanks as the hot water source at 90F. These would be only used for radiant heating, a separate tank is used for domestic. Delta T is 15F. Grufundos alpha pump. Zone controls.

2700 HDD
16,500 BTU heat load (calc via ManualJ)
10,000 (hydronic inc backloss), 6500 (baseboard/ele radiant)
3500 heated square feet


I assume that in this setup the best is floor sensor and air sensor. The low mass floors will respond quickly to the application of heat so a floor sensor alone would possibly cause the system to cycle on/off very frequently where the air temp was working against the floor temp. A air sensor alone will not allow the floors to be set to a decent temperature.

All comments appreciated.

Love my Ecobee. Took out overshoot in my house.

A low mass HR emitter shouldn’t have any controllability issues unless you have a very bad HR design/installation. It is the high mass HR emitters that need a little more controllability care to perform well. Your lack of a heat source using outdoor temperature feedback to continually and properly change the supply temperature (i.e., Outdoor Reset) puts you at a controllability disadvantage. Not being able to continually and properly decrease/increase the supply temperature when it is warmer/colder outside can result in the HR emitter providing too much/little heat gain given the lower/higher building heat loss at the warmer/colder outdoor temperature. A thermostat with both indoor air and slab temperature feedback can also significantly improve controllability. We commonly use the Uponor Setpoint 501S and the Tekmar 552 for our high mass HR emitters and they work very well. Again, having a proper HR design/installation does more to promote great controllability than the thermostat.