Thermostats
Our thermostats are easy to read, electronic, very sensitive, and use no mercury.
Radiant floor heating systems should be operated with thermostats that can maintain at least 1 degree differential.
All thermostats have a differential, that is the difference between the temperature the thermostat is satisfied and the temperature that it calls for heat. The setting that you set is only the temperature that the thermostat is satisfied. If it has a four degree differential and you set it for 70 degrees that means it will be 66 degrees before the heating system will begin to respond. Most radiant systems will drop another 2 degrees before they start catching up, now the air temperature is at 64 degrees. Because you notice the coolness you will set the thermostat higher, not because 70 degrees is not warm enough but because your thermostat allows the room to get to cold before it calls for heat.
Most people are setting their thermostats four degrees higher than they need to. Simply because their thermostat is to insensitive.
Number of thermostats needed
It is not practical to put a thermostat in every room for radiant heat. Lets start with the basement, if you have a small basement, one thermostat will probably work. If the basement is very large or is used for two proposes, such as sleeping and a recreation room or garage you will need two thermostats. Next is the garage, you will need one thermostat. Next is the main floor, smaller homes will need one for the living area and one for the sleeping area if the sleeping areas are not in the same area of the house you will need to add one. Most large homes will use three or four thermostats for the main floor area. Areas that are open to each other use only one thermostat. Small upstairs areas normally use only one thermostat, such as two or three bedrooms and a bath or two. Larger upstairs will require two thermostats or more. Do not put heat or thermostats in areas open to the downstairs.
Radiant systems need to be designed to respond quickly.
Radiant floor heating systems can be designed to respond relatively fast to heating demands. Operating a radiant floor heating system with a low water temperature or a modulating temperature control does not allow the system to respond quickly to demands. With the proper water temperature you can adapt to demands fairly rapidly.
As an example if your water temperature is 100° and you need to raise the room temperature 5° it could take two or three hours. But if you water temperature is 140° the room will gain 5° in less than one hour.