This paper reports that in uderfloor heating systems by using fix specific condition (temperature of supply water,design temperature of room, out temperature thickness of concrete on water tubes, coverage on the concrete, distance between water tubes,…) there is always an optimum convectional heat transfer of the air of the room that means when we have this convectional heat transfer in room we can get the maximum amount of energy from the supply water through concrete .we intruduce this parameter . We calculate the effect of thickness of concrete on the water tubes when using optimum convectional heat transfer coefficient that has effect on flux of energy obtained from the coverage (for example marbel) and claim that the less thickness of concrete, the more flux of energy we can get.