Buildings are one of the most important energy consumers in the world. High temperature gradients in heating systems can cause the increase of heat loss of the envelopes during the cold season and consequently increase the energy consumption. Floor heating systems has shown that they can generate lower temperature gradients in compare with other convective heating systems. In present study, the CFD simulation is done for a 3-D room and the required energy to achieve the thermal comfort in a room is calculated. The height of the room is changed and the energy loss of the room is calculated for both systems. Results showed that as the height doubles, the wall heat loss for radiator system almost doubles but for the floor heating system it was about 60 percent. This impressive result can recommend the floor heating systems for working areas with tall ceilings.