The impact of energy conservation between 1978 and 2010 on the utilization of existing and future district-heat production for a Swedish district-heating system are analyzed employing an end-use approach. The energy-conservation potential for space and water heating is calculated to be 35-40% of the final energy use in buildings located in the geographical area of the district-heating system and constructed before 1978. Based on results between 1978 and 1987, the estimated ratio between implemented measures and the calculated conservation potential is 75%. Energy conservation increases the ratio between the annual produced district heat and the design heat load. The connection of additional buildings to the district-heating system will compensate for energy conservation and result in a constant district-heat load and nearly constant marginal operating costs with efficient utilization of existing and future district-heat production. Cogeneration with biomass and energy conservation will together strongly reduce CO2 emissions, compared with a production system based on fossil fuels and without energy conservation.