Radiant floor heating systems require that you consider the effect of  radiant on the thermostat. Most thermostats simply measure the air temperature, although the air temperature is some what related to personal comfort. Floor radiant does present some unique differences.
   One problem that floor radiant can present is solar surge. This is caused when a large amount of south facing glass allows a large amount of solar energy to enter the house after a cold night. This causes a rapid rise in temperature. The sooner that the thermostat can respond to this problem the less effect it will have on your comfort.
   Two things are required to help prevent this problem. Place the thermostat so that it will heat up from this solar gain and respond quickly. 
   This applies only to rooms where solar gain is a problem.
    In other areas place the thermostat between 4 1/2 to 5 foot high, on the inside walls, and away from outside doors and heat sources. Do not place a thermostat in a hallway to control the bed room or on a upstairs area that is open to the downstairs.

It is not recommended to use a
set-back thermostat on a radiant heat system. Radiant heating systems do not respond as well as a convection type heating system, because a radiant floor heat system uses the mass of the
building to store heat and release it as needed.

CAUTION; Never put a stat on an outside wall. Be sure the hole in the wall behind the thermostat is closed. Cold air in the wall will cause the stat to give a false reading. Holes for electrical wiring or plumbing in the studs in the wall can direct cold air to the back of the thermostat.