A thermal block is any layer of insulating material that is placed on top of an underfloor heating system that prevents the heat from leaving the floor. Thermal blocks include obvious items such as large beanbag furniture or a futon with no air gap beneath it but also include less obvious items such as rubber backed rugs or even a pile of newspapers.
By preventing the heat from escaping the thermal block causes the floor beneath it to keep on heating up above it’s normal temperature and, unless the floor temperature sensor happens to be located beneath the thermal block, the heating system will not realise the heat is building up and will keep heating the floor. In extreme circumstances this can lead to the floor covering being damaged.
In-screed heating systems and cables covered in levelling compound or tiles do not suffer seriously from thermal blocks as the heat is conducted away from the area by the covering. Heat Mat’s underlaminate system is designed to help the heat work it’s way around the block through the aluminium heat dissipation layer however carbon films and heating ribbons can suffer very seriously with thermal blocks and with these systems it is vital to ensure you do not place anything on top of your floor that could prevent the heat from escaping.