124 



THE PRODUCTION AND USE OF HEAT 



the house. This practice is a saving of fuel, for none of the air 

 within the house is very cold at any time. A common practice, 

 which can be made to meet the wishes of all, is so to construct 

 the COLD AIR DUCT, as it is called, that the air may be taken 

 either from within the house or from the outside as is desired 

 'Fig. 91). 



FIG. 91. Furnace and air supply. 



143. Placing the Registers and Risers. The pipes which 

 lead up from the furnace open into the rooms by means of 

 REGISTERS, open frameworks of iron. The pipes leading from 

 the furnace to the second floor or higher are made of tin, 

 are rectangular in shape and usually about 3J^ in. by 12 in. 

 so as to be easily placed within a 4-in. wall. These hot air 

 pipes are called RISERS, or STACKS. 



One general rule should be followed: All heating pipes 

 should be as short as possible; all risers should be placed in 

 inside walls; and all registers should be placed as far as possible 



