The present paper describes a technical-economic analysis of thermomodernization works in multifamily buildings and public utility facilities constructed with the use of both traditional and industrialized technologies (prefabricated large-panel concrete, Zeranska brick), built before 1990. 1441 buildings located in 7 towns were analysed. The energy consumption indicator of the buildings undergoing the analysis was the indicator of heat load demand per cubic capacity, which was established on the basis of site inspections and technical documentation. The obtained results were used in analysing the cost-effectiveness of the suggested thermomodernization works. The following were adopted as criteria of the investment effectiveness: the ‘Simple Pay Back Time’ (SPBT), reducing the amounts of particulate matter and sulphur dioxide polluting the air, and heat load saving (amounting to a few or even several megawatts, which, in the case of a small town, is often sufficient to cover a prospective increase in heat load demand).