690 KANSAS CITY REVIEW OF SCIENCE. 
more than one) should be about one-sixth of a square foot for every pound of 
coal estimated to be burned hourly, in cold weather, and to prevent, in a meas- 
ure, the inconvenience of one hot-air pipe drawing from another, the collective 
area of the hot-air pipes should not be more than one-sixth greater than the area 
of the cold-air inlet. These proportions will admit the hot air at a temperature 
of about 120°, when at zero outside, and the velocity through the registers will 
not exceed five feet per second. 
A large heatin?; surface of the furnace is a well-recognized condition of both 
economy and efficiency. As a rule, there should be ten square feet of heating 
surface to every pound of coal consumed per hour, when in active combustion ; 
and the grate area should be about one-fiftieth of that of the heating surface. 
For the deficiency of heat, or the failure of some of the hot-air pipes of hot-air 
furnaces in certain winds and weathers in large houses or especially exposed 
rooms, the best addendum is an open fire-grate. With this provision in north- 
erly rooms, to be used occasionally, hot-air furnaces may be made to produce 
all the advantages of steam-heat in even the largest dwelling houses. 
Steam-heat may well be compared with stove- and furnace-heat : stove-heat 
corresponds to direct radiation by steam, and furnace-heat to indirect. The 
supply of fresh air from the outside to and over the hot-air furnace, and through 
hot-air flues into the rooms through registers, is virtually the same as when it is 
conveyed by means of steam-heated flues in the walls. Exhaust flues, for get- 
ting rid of foul air, are equally essential. The stove, as representing direct radia- 
tion in the same manner as the steam coil, or plate, in the room, has the advantage 
over the latter of some exhaust of foul air, however little, even when the smoke- 
pipe is not jacketed, for the steam-heat has none. In comparison with open 
stove-heat, steam heat is at still greater disadvantage ; for open stoves supply all 
the qualities of complete radiation — the introduction of fresh air and the escape 
of foul — to a degree wholly unattainable by steam-heat whether direct or indi- 
rect, or by hot-air furnaces, which always require special provision for the escape 
of foul air. 
The advantage of stove and furnace heat over steam may be summed up 
thus : It is more economical, more uniform, more easy of management, more 
suitable for small areas to be warmed, and is free from the noises and dangers of 
steam. Irregularities of the fire in steam-heating are a constant source of incon- 
venience, and sometimes of danger. The going down of the fire during the 
night-time, or its neglect for a few hours at any time, is followed by condensa- 
tion of the steam. On the addition of fuel and increase of heat, steam again 
flows quickly into the pipes where a partial vacuum has formed, and here, on 
coming in contact with the condensed water, it drives the water violently and 
creates such shocks as sometimes occasion explosions; or, at least, produces 
very disagreeable noises and general uneasiness, and frequently causes cracks 
and leaks. Hence direct steam heat, which for warming purposes alone is alto- 
gether superior to indirect, has been well-nigh abandoned. Indirect steam-heat 
places the leaks out of sight, but they commonly lead to mischief, and require 
special and expensive provision for access and repair. — North American Review. 
