For a variety of reasons, possibilities for reducing the use of expensive fossil fuel in central heat supply systems (CHSS) are currently being sought. One of the most effective solutions to this problem is the replacement of fossil fuels with cheaper renewable energy resources from local sources, in other words, diversifying energy resources in heat supply sources. The paper describes a mathematical model developed by the authors that can be used to compare and evaluate (from the economic and ecological perspectives) various alternatives for the diversification of fuels, thereby facilitating a quick and justified decision for the most advantageous solution. Approbation of the method developed by the authors has been carried out on the boiler house in the village of Ādaži, Latvia.