STEAM RADIATORS AND COILS Direct Radiators. The commonest forms of radiators to-day are the cast iron vertical loop varieties, types of which are shown m Figs. 2 and 13 in Part I (Heating and Ventilation). These are made up with slip:nipple or screw-nipple connections, the standard height being about 36 to 38 inches.
It is, of course, advisable to use radiators of standard height when possible, since they are cheaper than the lower radiators, which must be used when placed below window sills (see Fig. 10). Single-column radiators are more effective than those having a greater number of vertical loops, since in the latter the air flow is retarded and the cuter loops cut off the radiant heat from the inner ones. Radiators with four or more columns are generally used where the length of the space in which they must be placed is limited.
Wall radiators (see Fig. 4, Part I, Heating and Ventilation) have become very popular because of their neat appearance and the small distance they project into the room. They are very effective heaters, and, although more expensive than cer tain other types of cast-iron radia tors, less surface is required, which tends to offset the increased cost. These radiators are made up in such a variety of forms that they can be adapted to almost any location.
Concealed Radiators. A favorite method of concealing radiators is to place them below window-sills, with a grating or register face in front of and above them, as shown in Fig. 11. By this arrangement, the radiant heat is to a great extent cut off. The gratings must have ample area to permit the free circulation of air, and should have not less than 2 or 21- square inches of free area to each square foot of radiating surface, for inlets and outlets respectively. It is advisable to increase these allowances slightly when possible.
The same rule applies to radiators placed below seats. A radia tor designed specially for this purpose, for use without gratings, is shown in Fig. 12.
coils rest on hook plates (Fig. 13); the short pipes near the corner, on expansion plates (Fig. 14), on which the pipes are free to move when the long pipes expand. Such coils are very effective when placed below the windows of a factory, in which class of buildings they find their widest application.
Miter Coils. Miter coils, as shown in Fig. 15, are used for over head heating, the coils being suspended about 8 to 10 feet from the floor, and 3 to 4 feet from the walls.
A good type of hanger is shown in Fig. 16. The same type of coil, when placed alongside a wall, is known in certain sections as a harp coil (see Fig. 17), and may be used where long runs must be made along a wall, but where it is impossible to install the type of coil shown in Fig. 39, Part I (Heating and Ventilation), owing to doorways or other ob structions. Two harp coils could be used along a wall, for example, avoiding a doorway; and the expan sion of the pipes would be pro vided for by the short vertical lines.
Return-Bend Coils. Return bend coils, known in some parts of the country as trombone coils, are shown in Fig. 40, Part I (Heating and Ventilation). These are suit able only for rather short runs, since the steam must pass through the several horizontal pipes successively, and, if the radiating surface is greater than the capacity of the upper line of pipe to supply it properly, the steam is condensed before reach ing the lower lines. With the harp or other coils having headers or branch tees, sufficient steam can enter to fill all the pipes at once, pass ing through the parallel lines at the same time.