About 55% of over 14 million Polish households live in multi-family buildings. Cooperative or housing association buildings have a large share in this group. The heat is supplied from the district heating network or from local sources. With respect to facilities fed from gas boiler rooms, the signing and execution of fuel supply contracts is required. From October 1, 2017, the obligation to submit tariffs for gas trading set for all final customers (except for individual gas consumers in households) for approval to the President of the Energy Regulatory Office was lifted. Decisions regarding the choice of the supplier and the content of the concluded contract are made by the authorized bodies of the cooperative or housing association. The consequences of such decisions are borne by the owners and users of residential premises. Ensuring the continuity of a contract for the supply of gaseous fuel essentially comes down to establishing prices and rates in force for a given period. The right decision on the moment of signing the contract or the amendment, termination of the existing contract and signing a new one, or negotiation efficiency will result in financial profits for all users. The costs of heating and domestic hot water preparation are a significant component of the overall cost of the maintenance of flats in Poland. Therefore, it is even more important that the prices and rates agreed upon with the gas supplier are as favorable as possible to users. The high costs of heat are not only expenses for apartment owners. The attractiveness of flat on the rental market is also decreasing. The business activity carried out in facilities located in such buildings is also less competitive. The authors of the article analyzed gas prices on the Polish market over the last 3 years and presented the results of simulations of the effects of specific prices and rates set in the contract for the supply of fuel at the cost of heating from the point of view of a single apartment. As these are not large amounts per year, they do not motivate to optimize the terms of the gas purchase contract in this respect. The dynamics of changes in gas prices in Poland, although slightly different from world trends, is high. This makes it difficult for those responsible to make the decisions, and for residential users, it often means spending differences in subsequent years. One of the consequences of setting prices and rates significantly higher than obtainable may also be the reluctance of local communities to take measures to increase the energy efficiency of the heat supply system. From the point of view of heating costs, such decisions may distort the economic effect of thermo-modernization.