There are some limitations on what furniture you can place atop underfloor heating.
You should avoid any furniture that has a wide base and no clearance. For example, don’t place a mattress directly on the floor. You should also avoid using rugs.
These types of objects can trap heat underneath them, reducing the efficiency of the system and in some cases damaging the floor.
Furniture with at least 2-3 inches of clearance is okay. That gives the hot air enough space to circulate properly.