WAEMING AND VENTILATING OCCUPIED BUILDINGS. 295 



Dear a large fire-place in which a strong fire is burning. It is especially 

 in the large rooms of country-houses that these effects are most appar- 

 ent and unpleasant.* 



In other and frequent cases — especially In Paris, owing to the con- 

 fined kitchens, the proximity of water-closets, and the application of 

 ' weather-strips to the joints of doors and windows — the draught of a 

 chimney in which a strong fire is burning is supplied in part by the air 

 which has passed through those places, thus introducing into the living- 

 rooms unpleasant and unwholesome odors. 



5. Heating-effect of ordinary fire-places. — The hot air from the fire 

 passes out of the chimney at a temperature often at 140°, 175°, 212°, or 

 more. It carries with it and diffuses in space, without useful effect, the 

 greater part of the heat given out by the fuel.t This loss is as great 

 as sis-sevenths, seven-eighths, and more, of the heat produced, so that 

 what can be called the heating-effect of an ordinary fire-place scarcely 

 exceeds 12 or 14 per cent, of the total amount of heat produced by the 

 fuel. It is necessary then, while retaining the advantage of a quick 

 change of air, to restrict the amount and the temperature of the escaping 

 air to that necessarj^ to maintain the healthful condition of the room 

 and the force of the draught. 



6. Froportions necessary to secure change of air and draught. — A com- 

 mon chimney of the proportions usually adopted at present in Paris 

 removes in an hour on an average an amount, which equals and often 

 exceeds five times the capacity of the room it is intended to warm, and 

 this change of air will be suflBcient in rooms of the usual size to secure 

 a ventilation of over 1,000 cubic feet of air an hour for each person, 

 supposing there be more than one for everj- 10 square feet of floor-room. 



Again, in order that the draught should be sufQciently strong and 

 unaffected by the wind, it is only necessarj^ that the products of conibus- 

 tion should escape with a velocity of 10 feet a second in the case of a 

 fire of average intensity; but it is unnecessary, and even injurious, to 

 have so great a velocity in the main flue, where it should be only from 3 

 to 7 feet in a second, which is secured by making the flue sufficiently 

 large. 



The theoretical discussion of the conditions of the motion of air in 

 chimneys, and the results of experiment, lead to the following rules for 

 the proper i)roportions for chimneys in dwelling-houses.t 



7. Proportions of flues and shafts for private houses-. — For dwelling- 

 houses in the city or in the country, only a few stories high, where the- 

 walls that the flues are built in are of sufficient thickness, the chimneys 

 may be made of common bricks, and then the proper dimensions for the 

 flues as well as for the shafts at the top, according to the size of the 

 room, may be determined by the table given on the next page. 



* Essais i)olitiques, 6coiioniiques et philrsopbiques dn comte de Eumford, t, ler, p. DL. 

 t JEtudes sur hi ventUatiou, tome ler, cliap. 5, pp. 295 et suivants. 



