330 



VENTILATION 



vitiated, inside air out at the top of the window. In this man- 

 ner the vitiated air is being constantly diluted. 



When the dwelling is heated by means of a furnace, the 

 fresh air is admitted by means of a fresh-air flue, or intake, 

 entering the base of the furnace (Fig. 91). The circulation is 

 maintained by convection currents (Chap. I, Sec. IX). It is 

 evident that an outlet must be provided for the foul air. The 

 most efficient outlet is provided by an open grate, or fireplace, 

 especially if a fire is maintained in it. Explain why this is so. 



FIG. 233. Indirect radiation. 



When a dwelling is heated by steam or hot water, either of 

 two systems of ventilation may be employed. They are 

 known as the (1) INDIRECT RADIATION SYSTEM, and (2) the 



DIRECT-INDIRECT SYSTEM OF RADIATION. In the INDIRECT 



RADIATION SYSTEM the radiator is placed in a box-like compart- 

 ment beneath the floor. Fresh air is admitted through the 

 fresh air duct as shown in Fig. 233. It is heated as it passes 

 through the box surrounding the radiator and then passes 

 through the register into the room above. 



When the DIRECT-INDIRECT SYSTEM .is used the radiator 



