Abstract: The heating means of a greenhouse is combined with a source of waste heat. Preferably, the heating means is a surface heat exchanger placed in the flow path of air which is circulated in the greenhouse while the waste heat source is a mixing condenser of a steam turbine power plant. The condensate from the mixing condenser is cooled down in the surface heat exchanger which warms up the air in the greenhouse. If it has water spray means associated with it which is operated dependent on the moisture content of circulating air, cooling of the condensate and warming up as well as moistening of circulated air is effected by the same system at the expense of waste heat.