If a transition to heat supply takes place within a rental property in existing tenancies, e.g. by a contractor, Section 556c of the German Civil Code (BGB) and the associated Heat Supply Ordinance (Wärmelieferverordnung) have applied since July 1, 2013.
If, according to Section 556c I BGB, the tenant has to bear the operating costs for heat or hot water and if the landlord converts the supply from self-supply to independent commercial supply by a heat supplier (heat supply), the tenant has to bear the costs of the heat supply as operating costs if
1.the heat is supplied with improved efficiency either from a new plant constructed by the heat supplier or from a heat network, and
2.the costs of heat supply do not exceed the operating costs for the previous own supply of heat or hot water.