VENTILATION 



175 



window and the window-sill, and allow the air to enter from the 

 open window behind the board. Fresh air will enter and be deflected 

 upward toward the ceil- 

 ing; it then gradually 

 sinks and spreads through- 

 out the room. 



A piece of cloth 

 stretched on a frame and 

 fitted into the open 

 window makes another 

 type of ventilator which 

 is quite practical and 

 inexpensive. 



A wood or grate fire 

 is an excellent ventilator. 

 A heating system which 

 introduces warmed new 

 air is far better than a 

 heating system which 

 depends on direct radia- 

 tion. 



Difficulty of Ventila- 

 tion by Windows. We 

 have learned that fresh 

 air from outside will rush 

 into the room if the air 

 inside is lighter than the 

 air outside. This is usu- 

 ally the case during the 

 winter months. It does 

 happen in some climates 

 that the outside temper- 

 ature is the same or 

 nearly the same as the 

 inside temperature. 

 Windows may be opened in the morning, producing a satis- 

 factory amount of ventilation, but as the day gets warmer it is 



FIG. 138. Air circulating about a jacketed stove. 

 Fresh air is taken from out doors. 



