This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
It is advisable then, and then only, to use the lower arrangement. Radiators connected to a branch circulation-pipe are often on the one-pipe system, as shown in Fig. 539. A great saving of pipe can thus be effected, upon what would be required if both the flow and return pipes were carried along side by side, and the connections made as in Fig. 538.
Fig. 538 - Method of connecting Radiators to flow and Returns pipes.
Another arrangement of pipes is illustrated in Fig. 540, where each floor is shown to be warmed by a separate circuit. This arrangement is usually adopted in large buildings. Each floor can then readily be shut off, and means can be provided for emptying each of the mains separately at the points cc. It will be necessary to provide air-cocks at the highest point of each of the horizontal runs. It is often somewhat difficult to arrange a method of carrying horizontal pipes on upper floors; doors may be so placed that it is impossible to carry the pipes above the floor, and it may be very difficult to form a suitable channel in the floor itself.
For the heating of a ground-floor, the position of the pipes may be just below the basement ceiling, as shown in Fig. 533. This illustration shows the main pipe of wrought-iron 1½ inches in diameter, carried in the basement just below the ceiling, and from it arc taken off the branch How and return pipes to the radiator. The radiator should preferably be placed in a window recess, or, if the reveals of the window are not carried down to the floor, it should be plaeed as close to the wall as possible. An upward current of betted air is then created, which prevents cold draughts from pass-ing direct from the window into the room. Such radiators may be arranged to ventilate the room as well as warm it by direct radiation, if a suitable grating be arranged in the outer wall, and suitable baffle-plates inside; details of these have already been given in figs. 530 and 531. For the hall, a radiator of the type illustrated in Fig. 541 may be used.
Fig. 539.- Radiators on Branch Circulation-pipe.
In heating the rooms on the first-floor the same plan cannot be adopted, as of course the main pipe could not be carried through the best rooms on the ground-floor. One plan, therefore, is to prepare a special pipe-channel behind the skirting-board, as shown in Fig. 527, page 124, but even this is not always possible on account of doorways. The pipes, may, however, sometimes be carried between the joists, but should in all such cases be covered to prevent radiation of heat
Fig. 540. - Elevation of Low-pretaure Hot-water Apparatus, with Separate Circuit for Each Floor.
Fig. 541. - View of circular Radiator for Hall.
Another arrangement of pipes may be adopted, which consists in currying a main of suitable size entirely around the basement, just below the ceiling, and taking vertical flow and return pipes from this, as shown in Fig. 542. In the part lettered a, each radiator has a special flow and return; there is, therefore, nothing whatever to interfere with a good and efficient circulation. The only objection to the system is the number of pipes required. In part B another system is shown, in which there is only one vertical flow and one vertical return; the sixes might be 1 ¼ inches to the first branch, 1 inch thence to the second branch, and ¾ inch to the top radiator. It would be well to have a stop-cock close to the main, in both flow and return pipes, and if an outlet be arranged at c the whole of the loop can be emptied, except the short flow-pipe as far as the first branch. The disadvantage of such an arrangement as that shown, is that the water may flow past the ends of the branches without entering them. There is not the slightest risk about the top radiator, as that is sure to heat well, but there is always a danger that the ground-floor radiator may not get satisfactorily hot. In most of the illustrations, the flow and return pipes are shown to be connected with the same main-pipe, but in some cases, where there is a very long run of branch-pipe before it returns to the main, it is desirable to take the return-pipe back into the return-main, as shown in Fig. 539, page 132, as the two last radiators would receive water at too low a temperature to work efficiently, if the long loop were connected up to the flow-pipe only.
Fig 542 - Elevation of pipes for low-pressure Heating, showing two Arrangement* of Vertical Flow and Return Pipes for Radiators.
Another plan, which has been widely adopted in the United States, and generally referred to as the "Mills" system of piping, is to take the flow-pipe direct to the top of the building, and thence to take a number of pipes down as returns to the boiler, as shown in Fig. 543. Here the flow-pipe is carried up to the top floor, and feeds a ring-main carried round the building; from this ring descend vertical pipes to a similar ring in the basement, and from the latter ring is taken the return-pipe (or pipes) to the boiler. This gives a very satisfactory result, but if it be considered unwise to depend upon a single flow-pipe, it is easy to take a flow up to the top for each loop. This arrangement is well adapted for use in tall houses of four or five floors; it is, however, open to the objection that the hot water may pass the branches to the radiators without entering them, although it must be said that there is less chance of this in the present case than in that illustrated in Fig. 542. When only one flow-pipe is employed, it should have an area approximately equivalent to that of all the return-pipes taken together.
Fig. 543.-Diagrammatic View of the " Mills System of Piping for Low pressure Hot-water Apparatus. B, boiler; R R, radiator*: ap, air pipe; XT, expansion tank.