VENTILATION 



157 



waist ; the humidity must be kept low and the air must be in 

 constant circulation, to facilitate the removal of moisture. 



189. Circulation of air. Natural ventilation will often suffice 

 in dwellings that have large rooms and windows, with not 

 too many occupants. But when many 

 people have to be in a room, as in 

 schools and workshops (especially in the 

 winter, when artificial heating is neces- 

 sary), there is likely to be a need of 

 special attention to ventilation. So long 

 as the weather permits it, ventilation 

 should be by means of windows, open 

 top and bottom for the freest possible 

 circulation of air. A window board may 

 be placed under the lower sash, as shown 

 in Fig. 52, to prevent a direct draft ; this 

 will allow circulation of air between the 

 sashes and at the top. 



With closer occupation of rooms, 

 forced ventilation becomes necessary. 

 Several systems have been tried, in 

 thousands of buildings. In some the 

 air is pumped into the rooms ; in others 

 the air is drawn off. 



Fig. 52. Window venti- 

 lation in cold weather 



A board placed edgewise 

 under the lower sash pre- 

 vents drafts. The upper 

 sash is pulled down a few 

 inches, permitting fresh air 

 to come in between the 

 panes and permitting warm 

 expired air to pass out, as 

 shown by the arrows 



Experts are not agreed as to which is 

 better, and it is probable that neither is 

 altogether superior to the other. Which- 

 ever system is used, it can be combined 

 with a plan to filter the dust from the air 



that comes into the rooms, with a device for adding suitable quantities 

 of moisture, and with the heating plant for regulating the temperature. 



In artificially heated houses there is often the danger of having 

 the air too dry. In steam-heated rooms the moisture may be 

 maintained by having a dish of water on each radiator. 



