HEATING AND VENTILATION. 141 



no special provision for the escape of foul air, there is ordi- 

 narily sufficient renewal of the air. But in public buildings 

 there should be escape flues for foul air. 



Frequently in later years a large foul-air shaft is built in 

 some central part of the building, and a small stove placed in 

 it to create a sufficient up-current. 



In many public buildings the currents created -by heat are 

 insufficient to renew the air properly. Fans are used, which 

 force the air, properly heated, into the room. 



In heating by steam or hot water, if the radiators are 

 placed in the room they give direct, or radiant heat. This 

 system is called " Direct Heating." In itself it has no provis- 

 ion for renewing the air. It gives direct heat, and produces 

 air currents within the room ; and any change in the air is 

 wholly incidental, from escape of heated air in the upper 

 parts of the room and corresponding suction of outside air 

 through such openings as the carpenters have left below. 



In " Indirect " heating, coils of steam or hot-water pipes 

 are placed in air shafts which lead up to the rooms above, and 

 also have ducts to the outside. As the air is heated by the 

 heat of the pipes, it is forced into the rooms above, by fresh, 

 cold air pressing in through the ducts, to be, in turn, heated 

 and sent up. If there is at the same time a proper escape for 

 the foul air, this makes an excellent system. In many situa- 

 tions the direct and indirect may be advantageously combined. 

 Where there is a grate in a room it serves very well as a foul- 

 air shaft, especially when there is a fire in the grate. It is 

 well to have the flue from the grate in the same chimney with 

 that from the smoke-pipe, as then the heat from the smoke 

 will cause a constant up-draft in the grate flue, whether there 

 is a fire going in the grate or not. 



With a grate, in private houses, there is ordinarily no need 

 of other foul-air shaft for any room. But it is very desirable 



