Energy is a phenomenon that leads to conflicts, internal conflicts, and antagonism in all areas of life. Considering that we are dependent on foreign countries in the field of energy, the conservation of energy is getting more and more important day by day. A large portion of the energy consumed in Turkey is used to heat houses. It is very important to maintain the heat and keep it on the field as well as to heat the house. It is seen that the best and economical way of keeping the heat is thermal insulation in the apartments. In this study, five apartments in Erzincan which is in the 4th grade climate zone, have been heat insulated by using the mantle system according to TS 825. The annual energy requirement is calculated in the case of heat losses which occur in case of heat insulation and without heat insulation. As a result, it has been determined that the energy efficiency will increase if the apartments are heat insulated. It is also stated that the workmanship is important in heat insulation.