Why do you recommend Insulation Boards on a concrete base?
Warmup Insulation Boards
The insulation boards are used to prevent heat escaping downwards to the subfloor, improving the efficiency of the system.
Insulation boards can reduce running costs by as much as 50% because they are a highly efficient thermal barrier to cold rising from the subfloor.
By reflecting the heat upwards instead of losing heat to the subfloor, the floor will be warm in approximately 20 minutes after the system comes on. Without insulation boards it could take several hours.
See here for further information on the Warmup insulation boards.