HOUSE HEATING 417 



Power ventilation systems arc used in large public build- 

 ings, but they cannot be economically installed or operated 

 in the residence, small school, or public meeting place. 

 There are many simple methods of securing an influx of 

 fresh air and at the same time preventing draughts and zones 

 which are distinctly lower in temperature than the air in 

 other parts of the room. Among these may be mentioned 

 a deflection board or baffle set in front of a slightly raised 

 window, a muslin-covered frame inserted instead of or in 

 conjunction with the baffle, a hinged pane of glass where 

 the windows are made up of a number of small lights, and 

 where double windows are used the outer hung to open at 

 the bottom and the inner to open at the top. Transoms over 

 doors leading to the halls aid materially in the movement 

 of air, especially in a building of more than one story. An 

 open stairway acts as a flue, and the movement of air is 

 distinctly upward through it. 



Automatic controls. To obviate the necessity for watch- 

 ing the temperature of the house, simple devices, known 

 as thermostats, have been invented which will open or 

 close dampers and drafts with changes in temperature. 

 These devices involve the old principle of expansion and 

 contraction of metals and liquids with changes of tem- 

 perature. They are simple and require little adjustment 

 or attention. With the most common type two or three 

 dry cells once a year are needed. 



FUELS 



Coal. Fuels vary in actual value as much as wheat, 

 potatoes, butter, or any other article of commerce. Coal 

 is graded and priced, however, according to size instead of 

 quality. The finer the coal, the larger the percentage of 

 dirt, rock, and slate. Coal measuring from He of an inch 

 in diameter to % 6 is called buckwheat; that from %§ to % 

 of an inch, pea; that from 14 of an inch to ij4 inches, nut; 

 that from i}4 to 1^ inches, stove; and that from i$i 



