Risers are the pipes that pass from the lower floor to the upper floors and to which the radiators are connected by short pipes or nipples. These connections must allow for expansion, and it is advisable to put a valve into the lower end of every riser. By taking the steam from the top of the main, less water enters the riser.

Returns are the pipes that receive the water of condensation from the coils and conduct it back to the boiler room.