One of the most important factors of users comfort inside building is air temperature. From the other side one of the most biggest position in home budget is price for heat. Mutually exclusive indices are the cause that the control of temperature task using the smallest amount of energy as it is possible is very difficult. In this paper is presented simple model of temperature changes inside building base on lumped capacity method. Using this method finally obtains mathematical model of temperature changes which model is equivalent in structure to electrical RC- network. The model is composed of linear differential equations. Based on this mathematical model the simple algorithm controlling of temperature inside room is proposed. In this article are also included numerical simulations of the proposed solutions.