In general, it is prescribed that prefabricated slotted boards do not require filling, while for other modules, such as mushroom boards, filling is required. Doing backfill work can protect the floor heating module and floor heating pipeline against ground pressure on the one hand, and store heat and even heat on the other hand, making the floor heating experience more comfortable.
During construction, the gap between cement and sand is very large. Without backfilling, underfloor heating not only increases heat transfer downwards due to the reduced thickness of the modules used below, but also increases the heat generated by the cement mortar above. Too much space between the cement and sand will hinder the ability to dissipate heat upwards, resulting in a reduced heating effect.