TJic Principles of Ventilation. 



221 



the building when necessary, according to the third requirement of 

 perfect ventilation. 



The most common, because the cheapest and most easily managed, 

 apparatus on the indirect radiation plan, is the hot-air furnace. That 

 tiiere may be real ventilation with the use of this system, there are 

 necessary — although commonly omitted — appropriate ducts for the 

 removal of vitiated air. As applied in the majority of cases, this fur- 

 nace has a cold-air duct, of rectangular cross section, measuring fifteen 

 inches by six inches, or ninety square inclies ; hot air ducts, circular 

 or elliptical in section, leading to the various rooms, and no means for 

 tile heated air to escape, save through cracks or opened windows. The 

 cold-air ducts frequently terminate too near the ground, and in places 

 where boys at play may throw things into them. There are cases in this 

 city where, incredible as it sounds, the cold-air duct is omitted and the 

 air supply taken from the basement, at the floor level. Comment on 

 this procedure is unnecessary. It is not difficult to understand the 

 reason for such faulty arrangements. With suitable inlet and outlets, 

 more coal must be burned to maintain a comfortable temperature. It 

 seems proper to say here, that no one can expect to ventilate his house 

 without cost, any more tlian he can heat his hoifse without paying for 

 it. The relative cost of heating, merely, and heating with ventila- 

 tion is shown in the following extract from a paper by Eobert Briggs, 

 C. E., published in the third annual report of the Connecticut State 

 Board of Health. 



A certain school-room, when the outside thermometer stands at 

 zero, may be kept at the temperature of 70° by introducing 150 cubic 

 feet of air heated to 250° each minute. There is thus dispersed in 

 lieating 180° temperature that has been abstracted or taken away 

 from 150 cubic feet each minute, or 27000° cubic feet. If we suppose 

 in place of 150 cubic feet tiiere is given for ventilation 1000 cubic 

 feet each minute (50 scholars and 20 cubic feet each minute), it then 

 liappens that only 27° excess of tempci'aturc is demanded, and the 

 heat of the influent air becomes 97° in place of 250°. But there is 

 wasted each minute, in tlie one case, 150 cubic feet of air at 70"", 

 wliich has been heated up from zero, ^ 10500^ cubic feet, and in 

 the other, 1000 cubic feet at 70° = 70000^" cubic feet, or six and two- 

 third times as much heat in case of ventilating as in the case of 

 simple heating." 



The above comparison is made between hot air furnaces for the 

 heating and steam apparatus for ventilating. When the comparison 

 is made between steam heated hot currents and steam heated ventilat- 

 ing: currents, the numbers are 48000 and 97000, and these numbers 

 represent ^' the ratio of heating surface, boiler surface and fuel 

 consumed." 



