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If the lower opening, under the stove, is fed by air from the room, the effect is to consume rapidly the cold air near the floor and equalize the temperature in all parts of the room. A constant circulation is secured, and the warm air from the upper portion of the room is necessarily drawn down near the floor, to take the place of the air that is carried up through the stove.
Since the improved stoves I have described can be procured at a moderate increase of expense above the cost of common stoves, and since they combine most of the substantial advantages of steam and hotwater apparatus, and of hot-air furnaces, their limited use can only be accounted for by the fact that their advantages are not generally known.
The construction and arrangement of ventiducts is a question of vital importance, in connection with the heating of school-rooms.
Since the essential element of all ventilation consists in the ingress and egress of air, the subject would seem at first view exceedingly simple; but in practice it has been found one of the most difficult of all the questions that have tasked the ingenuity of educators and philanthropists.
The first ventilator of which the author has any recollection, was made about twenty-five years ago, and used in connection with one of Orr's air-tight stoves. It opened directly into a smoke-flue, and was placed at the bottom of a room, the lower part
being even with the floor. This secured a strong and certain action, and removed the air from the bottom of the room where it is coldest.
In many of our modern houses the ventilating registers are placed at the top of the rooms instead of the bottom. If a school-room is properly heated, that is, heated by the injection of a constant supply of fresh warm air, a ventilator placed at the top carries off the warmest and purest air of the room. The heated air conducted into the room rises directly to the top, and if it there finds a register opening into the ventiducts, it will of course pass directly off without being used at all. But if, on the other hand, the ventilating registers are placed either in the floor or in the bottom of the wall, the heated air sent into the room will first rise to the top, and then as the impure air near the floor is removed by the ventilators, the warm air above will pass down to take its place, and after being used and vitiated will pass off in the same way. The principal ventilators should not only be placed at the bottom of the room, but at the greatest distance from the inlet of the warm air.
A very excellent heating furnace, patented by Mr. Sawyer, is based on the principle of securing active ventilation from the lowest portion of the room. His ventilating registers are placed in the floor, and the impure air is conducted by tubes under the floor to the smoke-flues. This not only takes the coldest and most impure air from the room, but the ascending current in the smoke-flues necessarily secures a
strong and constant action of the ventilators. It is worthy of observation that this arrangement is substantially a reproduction of the ventilators used twenty-five years ago in connection with Orr's airtight stoves.
In constructing school-buildings, ventilating registers should generally be placed both at the top and the bottom of the rooms. In houses heated by common stoves, or by steam or hot-water pipes placed in the rooms, both the upper and the lower registers should ordinarily be kept open.
The foregoing remarks relate to the ventilation of school-rooms during the cold season. In the summer, when no artificial heat is required, the impure air from the lungs naturally ascends, and the upper registers should be constantly open.
It is not too much to say, that half the ventilators now found in our school-rooms are nearly useless. In rooms heated by steam with the pipes in the rooms, or by common stoves, it is very difficult to secure any but the most sluggish action, even when the ventiducts are properly constructed; and in most of the houses heated by the injection of warm air, the ventiducts are found to be either too small, or so badly obstructed as to be wholly inefficient. There are also hundreds of examples in which the ventiducts are made to terminate in close attics.
In a room intended for the accommodation of fifty or sixty pupils, the ventiduct should be not less than fifteen inches by eighteen, with a register having an equal amount of clear opening. In the construction
of ventiducts, care should be taken to give them a smooth surface, and to avoid all sudden turns or angles. The Emerson ventilating caps, placed at the outlets, are also important auxiliaries to the successful operation of ventilating flues.
If a smoke-pipe, or steam or hot-water pipe, can be made to pass through a ventiduct, its value will be greatly increased. When this is impracticable, the ventiduct should at least be carried up by the side of a smoke-flue. In one of the school-buildings of Chicago, a steam-pipe is carried through the length of each ventiduct. In the Philadelphia High School, the ventiducts all terminate in two ventilating chambers in the loft. In each of these is placed a large coal-stove, and from the top is a large cylindrical exit-tube. A large amount of heat may be generated by these stoves, at any season of the year, and an impetus given to the ascending current to any extent desired.*
When all other resources for ventilation fail, the teacher should resort to the windows. These can be opened freely before and after school, and at the
"The important points in the construction of a ventilator are, that it should, when possible, be a warm tube, and that it should open near the floor of the apartment to be ventilated. When warm, it constantly acts, from the mechanical tendency of a column of heated air to rise; whereas, if cold, it acts only when air is, by some means, forced into the room to be ventilated. In every other case, a cold ventilator is not to be relied on. A second point is, that its opening should be near the floor of the apartment, for it then carries off the stratum of air in contact with the floor, which is always the coldest, and usually the foulest in the room."--North American Review.
recesses; and they can be let down from the top, a few inches, during school hours, when the air of the room becomes unfit for use.
The following extract from a report prepared by a special committee of the New York Board of Edu cation, embodies a condensed summary of nearly all the valuable results that have yet been reached on the subject of heating and ventilation:
"That the building be warmed throughout (except the janitor's rooms, halls, and stairways) with fresh air, heated by contact with hot-water or steam pipes, or radiators, placed beneath the building; that the quantity of such radiating surface be at least one square foot to every fifty feet of the cubical content of the portion of the building to be heated; that if this do not amount to four square feet of radiating surface for each scholar to be accommodated in the building, then that amount be put in; that the boilers shall be capable of boiling the water, or of generating abundant steam in the coldest weather, and the smoke-pipe shall not in any case show a temperature of above 350°; that the draught of air into the furnace of the boiler, of water into the boiler, and of cold air into the stacks of pipes or radiators, be governed by automatic regulators; that the boilers shall not require replenishing with fuel oftener than once in every four hours; that the radiating surface be divided into separate stacks, one or more for each room, and that the ventilating flues be separate, with openings into the room both at the top and the bottom of the room, and equal in aggregate sectional area to the sectional area of the cold-air boxes, which shall not be less than one square foot for every hundred feet of radiating surface; that the contractor shall give security satisfactory to the Board of Education that he will keep the apparatus in repair for five years, and that it shall in all weathers heat every portion of the house to 70°, and furnish ventilation at the rate of ten cubic feet of air per minute to each scholar to be accommodated by the building, the air to be so introduced into the rooms as to produce no unpleasant draught."