Low-grade heat is of rapidly increasing importance in Sweden and, therefore, so is the economic evaluation of such heat. The present heat cost is based on a detailed feasibility study of large-scale heated horticulture combined with electricity production from a Swedish boiling water reactor power plant. To estimate judiciously the cost of heat from a dual-purpose plant—such as a large-scale horticultural installation combined with and using low-grade waste heat from an electric power plant—is an almost classical problem; a measure of arbitrarity is unavoidable. The opportunity cost approach shown has presumably some new features. Incidentally, it results in an estimated cost of heat delivered from the turbine condenser heater in the power plant of 1.4 $/GJ (or 6.1 Swedish Crwn/GJ) in 1980, which is less than one-third of the cost of fuel only with conventional oil-fired heaters.