160. Hot-water Heating.—In hot-water heating a furnace arranged for heating water is placed in the basement. (See Fig. 142.) Attached to the top of the heater are pipes leading to the radiators in the various rooms; other pipes connect the radiators to the bottom of the boiler. The heater, pipes, and radiators are all filled with water before the fire is started. When the water is warmed, it expands and is pushed up through the pipes by the colder water in the return pipe. The circulation continuing brings hot water to the radiator while the cooled water returns to the heater, the hot radiators heating the several rooms.
161. Steam Heating.—In steam heating a steam boiler is connected to radiators by pipes. (See Fig. 143.) The steam drives the air out of the pipes and radiators and serves as an efficient source of heat. Heating by steam is quicker than heating with hot water. It is therefore preferred where quick, efficient heating is required. Hot water is less intense and more economical in mild weather and is often used in private homes.
Fig. 144.—Heating by an indirect radiator with side-wall register.
162. Direct and Indirect Heating.—In heating by direct radiation (Figs. 142, 143), the steam or hot-water radiators are placed in the rooms to be heated. With direct radiation, ventilation must be provided by special means, such as opening windows, doors, and ventilators. Sometimes radiators are placed in a box or room in the basement. Air from out of doors is then driven by a fan over and about the hot radiators. The air thus heated is conducted by pipes to the several rooms. This arrangement is called indirect heating. (See Fig. 144.) The latter method, it may be observed, provides both heat and ventilation, and hence is often used in schools, churches, court houses, and stores. Since heated air, especially in cold weather, has a low relative humidity some means of moistening the air of living rooms should be provided. Air when too dry is injurious to the health and also to furniture and wood work. The excessive drying of wood and glue in a piece of furniture often causes it to fall apart.
Fig. 145.—An automatic air valve.
Fig. 146.—An automatic vacuum valve.