The article contains reviews the method of optimization of gas supply of CHP sources of energy - the method of calculation of permissible IRR. It is effective for analyzing the projects of CHP plants’ gasification (also in reconstruction of existing boiler houses). IRR is an effective criterion of profitability of gasification, if the forecast of the consumption of gas is precise. Using the method of calculation of permissible IRR it is possible to find the load limits in which CHP plant must work, so that the project of gasification be efficient.