The coil may be arranged on a flat wall-surface so as to form a mitre branch-tee coil as in Fig. 93, lower part, or with both branch-tees at one end and elbows and nipples at the opposite end; the fittings at ends being connected by pipes having the proper pitch. Such a construction is called a return branch-tee coil, see upper part Fig. 93. The coil may be arranged on two sides of a room with the elbows placed in the intervening corner, in which case it is called a corner coil.

The various types of branch-tee or manifold coils as described present small frictional resistance to the flow of steam or water and give satisfactory service for either steam or hotwater heating.

FIG. 93.-BRANCH-TEE MITRE COIL AND RETURN-COIL.

If two connections are used the steam should be supplied at the highest point of the coil, and the return taken off at the lowest; if one connection, steam is to be supplied at the lowest point. The horizontal portion should be given a

pitch of one inch in ten or twelve feet, and an air valve or cock should be connected to each coil. When several return-bend coils are grouped together, as in Fig. 94, the construction is termed a box coil. This has all the faults in an aggravated manner that were ascribed to the return-bend coil, and in addition causes a loss of efficiency due to close grouping of surface.

The pipe coils, Figs. 92 to 94, will do equally well for steam or hot-water circulation.

65. Vertical Pipe Steam-radiators. These were at one time used extensively, and were made by screwing short pieces of vertical pipe into a cast-iron base and connecting the pipes in pairs at the top with return-bends, which were usually screwed but sometimes pressed on. One form still in extensive use was made by screwing pipes, having the upper end closed and provided with an internal diaphragm, into a cast-iron base. The diaphragm being so placed as to produce the same circulation in one pipe that was obtained in two pipes with the other form.

The pipes are arranged in two or more rows as necessary to secure the desired radiating surface. In early radiators of this class the base was provided with a diaphragm, and each return-pipe was trapped by a cavity filled with water so as to insure a continuous circulation of the steam through each pipe. In some of the recent radiators the return-pipes are trapped

as explained above; but in nearly every case the base is entirely open and arranged so that it will drain freely, no attempt being made to force circulation in any direction. In some of the recent radiators of this type the base, instead of being in one piece, is made up of sections connected by nipples, so that

it can be lengthened

or shortened at pleasure. An air-valve must always be provided with these radiators, the best location for which is at about one third the height of the radiator, and on the end opposite the admission.

The wrought iron radiator is constructed in nearly every case of one-inch pipe, taken of such length that there is one square foot of exposed radiating surface for each

pipe in the radiator. The form being quite regular its surface can be accurately measured.

66. Cast-iron Steam-radiators.-Cast-iron radiators are now mostly used in direct heating.

Those principally used have vertical radiating surfaces, and are made either by screwing loops or sections into a hollow base provided with the requisite openings, or by connecting at the bottom a series of parallel vertical sections by nipples screwed from the outside or inside of the base. The first form of radiators, having a base of fixed dimensions, is often called the standard form; the latter, which can be increased or diminished in length by adding or taking off sections, is called a sectional radiator.

The radiator is in some instances provided with a flat top which is held in place by screws, but the greater portion of

those of recent design have a highly ornamented surface and

are used without top or screen of any description. The illustrations, Figs. 93 to 106, give a very fair idea of the appearance of those in use. They are painted in various colors, enamelled or bronzed, as may be required by the house owners or architects.

The efficiency of direct radiation is somewhat increased by painting or bronzing, but is lessened by varnishing or enamelling: but that of indirect is not so affected.

These radiators are made in great variety of forms, and can be had of such shape as to surround columns, or fit in corners; and of almost any height desired. Some of the radiators are fitted with warming closets.

FIG. 96.

STANDARD CORNER RADIATOR.

(See Fig. 98, frontispiece, for illustration of styles in use.)

*With permission from Heating and Ventilation.

4

The sectional radiators are in many cases built in such a manner as to form flues for the passage of air from the bottom to the top of the radiator for the purpose of increasing the airheating capacity. Such radiators are termed flue radiators (Fig. 99).

Radiators are sometimes built with projecting fins or ornaments of cast iron for the purpose of greatly extending the surface in contact with the air. Such a radiator is termed an extended surface radiator, and is now little used for direct heating (Fig. 100).

The radiators in principal use are constructed as described, but radiators have been built by many other methods and in many other shapes. They have been constructed of one solid. casting, and by uniting sections of various forms by bolts and packed joints.

67. Hot-water Radiators.-Hot-water radiators differ essentially from the steam-radiators in having a horizontal. passage at the top as well as at the bottom. This construction is necessary in order to draw off the air which gathers at the top of each loop or section. Aside from this the construction may be the same in every particular as that for steam-radiators; in