This supplement to the guideline VDI 2077 applies to the consumption-based billing for heating systems in which, for design-inherent reasons, a considerable amount of the heat to be supplied to the consumer units is lost through pipes, but usually remains unaccounted-for. Such heating systems are, in particular, vertical single-pipe heating systems with non-insulated trunk lines and, e.g. , horizontal single-pipe heating systems of the Rietschel- Henneberg type (non-insulated ring line, see Bibliography). It is irrelevant, from the technical point of view, if the piping in question is exposed or inwall. The heat loss through these pipes may have a significant impact on the accuracy of heat cost allocation. This guideline gives recommendations for reducing the heat loss through pipes and specifies methods for considering the heat loss through pipes in heating-costs billing so as to avoid cost distortions.