The objective to obtain the recommended (at least 50% by weight) level of recycled and reprocessed raw fractions of municipal waste in the perspective of 2020 might in turn contribute to the deterioration of the fuel properties of waste stream that is intended for incineration. In order to avoid oversizing heat recovery plants their construction should be based on well-defined properties of the waste fuel. The author carried out simulation calculations of the impact of changes in the composition of municipal waste on their energetic properties. The calculations of the calorific value of the waste fraction (so called combustible fraction) with the potential to be used as an alternative fuel were done.