1 8 HEAT 



As the air is heated by the fire it expands, and is pushed up 

 the chimney by the cold air which is constantly entering through 

 loose windows and doors. Open fireplaces are very healthful 

 because the air which is driven out is impure, while the air 

 which rushes in is fresh and brings oxygen to the human being. 



But open fireplaces, while pleasant to look at, are not effi- 

 cient for either heating or cooking. The possibilities for the 

 latter are especially limited, and the invention of stoves was a 

 great advance in efficiency, economy, and comfort. A stove is 

 a receptacle for fire, provided with a definite inlet for air and a 

 definite outlet for smoke, and able to radiate into the room most 

 of the heat produced from the fire which burns within. 

 The inlet, or draft, admits enough air to cause the fire to burn 

 brightly or slowly as the case may be. If we wish a hot fire, 

 the draft is opened wide and enough air enters to produce a 

 strong glow. If we wish a low fire, the inlet is only partially 

 opened, and just enough air enters to keep the fuel smol- 

 dering. 



When the fire is started, the damper should be opened 

 wide in order to allow the escape of smoke ; but after the 

 fire is well started there is less smoke, and the damper may 

 be partly closed. If the damper is kept open, coal is rapidly 

 consumed, and the additional heat passes out through the 

 chimney, and is lost to use. 



9. Furnaces. HoJ Air. The labor involved in the care of 

 numerous stoves is considerable, and hence the advent of a 

 central heating stove, or furnace, was a great saving in 

 strength and fuel. A furnace is a stove arranged as in 

 Figure 13. The stove 5, like all other stoves, has an inlet 

 for air and an outlet C for smoke ; but in addition, it has 

 built around it a chamber in which air circulates and is 

 warmed. The air warmed by the stove is forced upward by 

 cold air which enters from outside. For example, cold air 



