This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Fig.. 49, 50 and 51 show the common methods of making the connections between the supply pipes and the radiators. Fig. 49 shows a two-pipe connection with a riser; the return is carried down to the main below. Fig. 50 shows a single pipe connection with a basement main and Fig. 51 a single connection with a riser.
Care must always be taken to make the horizontal part of the piping between the radiator and riser as short as possible and to give it a good pitch toward the riser. There are various ways of making these connections especially suited to different conditions, but the examples given serve to show the general principle to be followed.