What has been said as to plumbing is particularly true of the steam heating. The radiator in a room is the only outward evidence we can see of the heating apparatus in apartments. The size of the radiator and the quality of the air, and the controlling valves, may be considered; also the radiator should be placed in front of a window, or as near a window as possible, so as to give the greatest amount of efficiency with the least amount of heat consumption. Radiators are often ill placed for the sake of saving rising lines to connect them, or to overcome the expense of running long lines of branches.

Horizontal tubular boilers, or upright sectional boilers, are most commonly used for heating apartment houses and business buildings. High pressure heating plants are used where power is required, or where a great deal of heat is necessary, and in such cases the boilers are made to carry a minimum pressure of 80 lbs. of steam and upward. In low pressure plants the minimum pressure necessary to obtain results may be only two or three pounds of steam, the maximum not more than ten pounds. A sectional boiler is rarely or never employed for high pressure work. It is less satisfactory, although cheaper than the horizontal boiler.

Large or small sizes of coal may be used by adapting the style and size of the grates to the kind of coal desired. The small sizes of coal, known as "steam sizes," burn more rapidly, and are particularly adapted for high pressure plants, but require more constant "firing" than the larger sizes.