Efficient design

The performance of the insulation layer

The performance of a radiant system depends particularly on the layer of thermal insulation used to limit heat loss between the tubes and the space behind them. Standard UNI EN 1264-4 sets out limit values of thermal resistance for systems that work as both heaters and coolers, and recommends them for systems dedicated to cooling only.

The amount of thermal resistance, indicated by the letter R, depends on the material (on the thermal conductivity) and on thickness, temperature and humidity. The designer can use the thermal resistance value obtained from the thermal conductivity data declared (λd) by the manufacturer (which refers to precise standard values of temperature and humidity), or can correct the value on the basis of real-use conditions , defining a design thermal conductivity for the project (λp) (in accordance with UNI EN 10456).

The limit values of thermal resistance depend on the temperature of the room adjacent or below, as shown in the following table:

Room adjacent or below

Insulation resistance [m2K/W]



Not heated


Heated but not continuously


Directly on the ground


Design external temperature ϑe > 0°C


Design external temperature -5°C <ϑe < 0°C


Design external temperature -15°C <ϑe < -5°C