"The COTIMO concept represents an Energy Efficiency technology which saves heating energy of buildings. It does its job through a unique intelligent control of the heating system. This technology can save easily 5 to 10% heating energy per year. The cost of implementation is cheap compared to other energy efficiency alternatives. The operation of the concept is described in this work. Measurements, simulations were done to get almost real saving data. These efforts let an insight to the performance of the concept. In 2013 the world's population consumes more than the earth can give. Sustainability questions arise again and again regarding energy, air, water. After years long study of different renewable energy solutions, one thing has to be told: using Renewable Energy always has to be the second step. Energy Efficiency comes first. The concept works best at buildings with low RC time constants and at low frequency occupancy changes. The simulations resulted saving values between 2% and 11%. This domain is lower than other papers declare in the literature. It is not recommended to install the system in case of high frequency occupancy changes. In such cases the building's heat consumption may be higher than without the system. Cinemas, conference centres, weekend houses, university auditoriums, schools, sport halls, churches are only a few examples where the concept may be successful."