7531 Heat distribution systems - Steam and condensate (2) Piped systems, using steam as the heating medium, distributed to heat-using plant or equipment and returning condensate to the steam generating equipment 7532 Direct steam systems (0) Piped distribution systems providing a steam supply for direct uses and process requirements, complete with condensate return 7533 High temperature high pressure hot water heat distribution systems (0) Piped systems, using high temperature high pressure hot water as the heating medium, distributed to heat-using plant or equipment 7534 Medium temperature hot water heat distribution systems (4) Piped systems, distributing medium temperature hot water to user points 7535 Low temperature hot water heat distribution systems (6) Piped systems, distributing low temperature hot water to user points 7536 Hot oil heat distribution systems (0) Piped systems distributing hot oil to user points