Abstract The main aim of the thermomodernization of historic churches was to reduce energy consumption for heating and improve air quality by reducing the amount of pollutants emitted into the atmosphere. Calculation methodology was adopted in accordance with the Decree of the Minister of Infrastructure on the detailed scope and form of an energy audit [4] , [5] and based on the fuel indexes (WO) and CO2 emission (EC) for reporting under the Community Emissions Trading [13] . We have achieved a significant reduction of the annual heat demand and the reduction of emissions: SO2, NOx, CO2 and dust as a result of the modernization, with the exception of the Church in Chlopkow (No. 1). The results of the energy and environmental analysis show the validity of the religious buildings thermomodernization and upgrading their heat sources. These effects are necessarily connected with the economic effects. Practical application of this paper was to show the possibility of carrying out thermomodernization upgrades for reducing demand for heating, for thermal power and protecting the environment.