Under the current legal situation, companies that place certain energy sources on the market have to pay a certain carbon dioxide price, which they regularly pass on to their customers. Under the previously applicable legal situation, a landlord could pass on the carbon dioxide costs included in the heating costs in full to the tenant if there was a corresponding contractual agreement. Effective as of 1 January 2023, the Carbon Dioxide Cost Allocation Act (Kohlendioxidkostenaufteilungsgesetz – CO2KostAufG) came into force, the purpose of which is to allocate these carbon dioxide costs between landlord and tenant. In the case of rented rooms in buildings that are predominantly used for residential purposes (residential buildings), the maximum carbon dioxide costs to be borne by the tenant are to be determined according to a graduated model, which is essentially based on the carbon dioxide emissions of the rented property. For rooms in non-residential buildings, the landlord must bear at least half of the carbon dioxide costs. It is expected that in 2025, the legislator will also introduce a graduated model for rented rooms in non-residential buildings. When concluding lease agreements, the regulations of the CO2KostAufG should be taken into account by including appropriate clauses in the lease agreement.