109. It is common practice to place radiators, hot-air registers, and stoves near the inner end or corner of a room. This proceeding is wrong in principle; the only advantage that can be gained by such an arrangement is that the heating apparatus is thereby concentrated near the center of the building, and consequently the amount of horizontal piping required is less than it would be if they were placed near the outer walls. A small economy in first cost is thus secured, but the efficiency of the apparatus is sacrificed.

The main objection to placing hot-air registers and ducts in the outer walls of a building is that the hot air is likely to be chilled and thus the circulation impaired. This may be prevented, however, by providing the duct with a proper covering' of non-conducting material upon the outer side. The heat which escapes from the inner side passes into the room and does useful work.

Direct radiators should always be located near the outer walls, or where the cooling influence is greatest.

Direct-indirect radiators are necessarily placed against the outer walls, and therefore are usually located properly.

Indirect radiators should always be located at a sufficient distance below the hot-air register to cause the air to pass through them at a proper velocity.

In factories and workshops, pipe coils are often placed overhead, suspended horizontally at a distance of not less than 4 feet above the heads of the workmen, and not less than 1 foot below the ceiling. The machinery, and the belting which drives it, will carry the heated air downwards towards the floor, and will usually diffuse it throughout the apartment in a satisfactory manner. Overhead heating, however, is not satisfactory when the air is not in perceptible motion.