METHODS OF HEATING 



343 



to heat a home it is necessary to have a stove in each room. 

 A large furnace in the cellar overcomes these drawbacks, and 

 is consequently used in most houses. From the furnace, hot 

 air is distributed through ducts to 

 the different rooms. Such a fur- 

 nace draws in fresh outside air 

 and passes it into a dome over 

 and around the hot coal. As the 

 air becomes hot, it expands, and 

 thus makes its way to the several 

 rooms. 



Steam radiates its heat with 

 ease, and also condenses very 

 rapidly. Heat given off by a 

 furnace is called steam 



FIG. 172. Heating by Stove. 



steam 



heat and may be provided direct- 

 ly or indirectly. Direct heat is given off by radiators in the 

 room to be warmed, while indirect heat is supplied by dis- 

 tributing throughout the building air that has been warmed 

 by passing over radiators in the basement. 



Wood and coal stoves, gas heaters, steam and hot-water 

 radiators, coils of heated pipe, and electric resistance heaters 

 are all examples of direct radiation. The air in a room is 

 heated over and over again, and fresh air is admitted usually 

 only by leakage around doors and windows or by the opening 

 of one or the other. 



384. Steam Heating. Steam for heating (Fig. 173) is 

 obtained from a boiler fitted with coils of pipe. As the steam 

 passes through the radiator it gives off its heat and is con- 

 densed into water. This water flows back into the boiler, 

 either through another return pipe or through the same pipe. 



