302 WAEMING AND VENTILATING OCCUPIED BUILDINGS. 



be less unhealthful, beeause the hot air which it furnishes is always at 

 au excessively high temperature. 



The removal of the foul air of the room, also, is rather diminished 

 than increased, since the temperature of the escaped gases is less. 



19. Stoves with circulation of air made on the model devised by the late 

 Rene Duvoir and the General Gas-Light Company. — These stoves, with 

 which some schools in Paris are provided, and which are recommended 

 to the public by the General Gas-Light Company for coke-burning stoves, 

 utilize 67 per cent, of the heat produced by the fuel. 



The escaping products of combustion often have at 13 feet from the 

 fire a temperature of 750° or more. The warm air which passes into 

 the room is as high as 392°, and its volume is only 800 cubic feet for 

 each pound of coal burned, because the passages provided for it are 

 much too small. Those of the usual proportions only produce a change 

 of air of about 2,119 cubic feet an hour, or 352 cubic feet to the pound 

 of coal. They are consequently unhealthful, and do not merit the name 

 of ventilating stoves, which some makers give to them. In order 

 to make them cheap, most stoves of this kind are made with the 

 total heating-surface scarcely equal to twenty times that of the grate, 

 while it should be at least three or four times as much. The surface of 

 the hot-air passages is scarcely equal to that of the grate. This should 

 also be three or four times as much, to increase the amount of air 

 introduced and to reduce the temperature. 



The chimney has an area equal to 18 per cent, of that of the stove. 

 It would be well to double it to secure at least a more rapid chauge of 

 air ; but then the heating-eftect of the apparatus would be materially 

 reduced. 



20. Portable heaters — Ghaussenofs and similar models. — (Fig. 13.) — 

 This builder has made, for large rooms, hall-ways, &c., stoves with hot- 

 air circulation, which are true heaters, because, before escaping into 

 the air, the products of combustion pass through many pipes, and a 

 considerable amount of warm air may be obtained, drawn, if necessary, 

 from the outside of the building. Their heating effect is as much as 

 93 per cent, of the heat i^roduced by the fuel. They are capable of in- 

 troducing into the places to be warmed about 2,551 cubic feet of air for 

 each pound of coal consumed, but the temperature of the air is as high 

 as 266"°, or even more, which shows that the passages are not sufflciently 

 large. With their present proportions, they only remove 91 cubic feet 

 of foul air for each pound of coal burned. They are, consequently, un- 

 healthful, and are only suitable for warming passages, such as vestibules, 

 stairways, &c., where the external air enters and mixes freely with the 

 warmed air. In a stove of this kind experimented upon at the conserva- 

 tory, the total heating-surface is more than one hundred times the grate- 

 surface, which is a good and large ratio. The surface of the air-passa- 

 ges is equal to three times the grate- surface, which is not quite enough. 



The chimney has an area equal to 47 per cent, of the grate-surface. 



