286. The requirements for the successful ventilation of the various classes of buildings which are occupied by human beings are alike in principle in all cases, and have been fully considered in the preceding articles. The architect should bear in mind that ventilation is a sanitary necessity, and should realize that the physical health of those who occupy the premises depends in a large degree upon the skill and faithfulness with which the work is planned and executed.

Considering the matter from a sanitary standpoint, the problem of ventilating an ordinary dwelling, containing from four to eight rooms, must be regarded as the most important, because the vast majority of our people are housed in that kind of building, and are vitally affected by the conditions prevailing in them.

Schoolhouses come next in importance, being occupied by large numbers of children for from four to six hours per day. Children are much more susceptible than adults to insanitary influences, and must therefore be guarded with the utmost care.

Next in importance are the manufactories, containing large numbers of people engaged in labor for from eight to twelve hours per day. Public buildings, such as theaters, churches, audience rooms, and legislative halls, although they receive the greatest share of public attention, are really of less importance to the sanitarian, because they contain comparatively a smaller portion of the population, and are occupied only for short periods of time.

The chief impediment to good domestic ventilation is the expense of the apparatus. Much of the apparatus now on the market is needlessly complicated and costly, and is encumbered with numerous "attachments" which are more profitable to the vender than the purchaser.

287. It is impracticable to ventilate a dwelling in a proper manner while direct heaters of any kind are used for warming it. The heaters, whether stoves or radiators, must be converted into direct-indirect or indirect apparatus; and the foul air must be vented positively and continuously. The inlets and outlets of each room must be managed so that there will be no considerable difference of temperature in any part of it.

These results can be attained only by employing some system of aspiration, mechanical ventilation being assumed to be impracticable on account of expense. Foul-air ducts of suitable size, and having sufficient height to draw well, must be provided; they are, in fact, indispensable.

These ducts should be brought together and connected into a good chimney. The smoke pipe from the kitchen stove or the heating apparatus should extend up through this chimney such a distance that there will be no chance of having a poor draft for the fire. The pipe inside of the chimney should be made of cast iron, to withstand corrosion, and it should be braced so as to stand in the center of the flue rather than at one side. It is better to make one large flue, with a smoke pipe inside of it, than to build a pair of flues, one for foul air and the other for smoke. In all but the smallest dwellings, two such foul-air chimneys should be provided, one taking the smoke pipe from the kitchen range, and the other from the furnace or boiler. This permits the foul air to be disposed of with a minimum amount of piping.

The doors and windows should be made as nearly airtight as possible, so that cold air cannot enter the building except through the proper channel, that is, through the heating apparatus.

288. One of the chief difficulties to be found in securing a proper distribution of warm air in the several stories of a dwelling is the draft that always exists to a greater or less extent on the stairway. An upward current of considerable force prevails here at all times while the heating apparatus is in use, and if there is any mode of escape for air at the top, this draft will be so strong as to interfere with the proper suction of the foul-air flues. While this trouble may be avoided by enclosing the stairs and placing doors at the foot or head, this remedy is usually so objected to that it may be dismissed as impracticable.

If the hall is located in the middle of the building, so that it is warm on both sides, the stairway draft may be utilized to operate the ventilating system. The foul air may then be drawn out from each room into the hall through the space under the doors, these spaces being made of proper size to serve as foul-air exits.

At the top of the stairway the air should be discharged through an aspirating shaft, and not through a skylight or ventilator. If the skylight is used for this purpose, a current of cold air is likely to enter at one part of the opening, while warm air flows out of the remainder; thus, the cold air will pass down the stairs, making very unpleasant drafts.

When the hall is employed in this manner, all the larger rooms, especially those on the first floor, should be provided with additional foul-air outlets. An open fireplace serves excellently for this purpose, provided the opening into the chimney is not too large or too far above the floor. A fireplace, as explained on another page, is a poor contrivance for heating purposes, but it can be made a useful assistant to ventilation.

289. In dining rooms and parlors, where gas burners or oil lamps are used for illumination, it is a good plan to enclose the lights in glass, and provide them with a special draft tube connected to the foul-air flue. This arrangement not only disposes of the products of combustion, but it will, if properly constructed, add considerably to the brilliancy of the light. It also furnishes a local vent which serves admirably to clear the room of the fumes of cigars, etc.

290. A common method of ventilating sleeping rooms is to provide two openings into the hallway, the door being raised an inch or more above the floor, and the transom being opened above it. This device, however, is inoperative, because there is no force tending to drive the air either way through these openings. If any fresh air reaches the occupant of such a room, it will be by leakage through or around the window. If the window is open, and the weather is quiet, the air from the hall is likely to pass through the room and escape at the window, thus making the chamber a passageway for vitiated air.

291. The bathroom should be thoroughly ventilated and warmed. As usually constructed, in the smaller class of dwellings, the bathroom is but little larger than a closet; and when a warm bath is taken, the air is quickly vitiated, to a serious degree, by the combined effects of moisture, heat, gas burners, and respiration. Where no positive ventilation is provided, this bad air, in conjunction with a warm bath, is very exhausting. The practice of ventilating a kitchen into a bathroom is entirely wrong, and should not be allowed.

292. The water closet should be provided with a special ventilating flue, or local vent, and care should be taken to insure a draft in it that will never be reversed. This pipe should take air from under the seat, and should, if practicable, be run alongside of the kitchen chimney, and up to the top of the building, independently of all other pipes, and should also be provided with a gas burner or other artificial heat to secure a positive draft when the chimney is cold. Outlet registers in water-closet apartments should be set close to the water-closet seat.

293. All clothes closets should be ventilated, especially those which receive undergarments or soiled clothing. The openings from these closets should be protected with fine screens to keep out moth millers, etc.

294. The kitchen and laundry should be ventilated independently of the other parts of the house, and if there is any door opening directly from them into the hall or stairways, it should be made practically air-tight, otherwise the odors of cooking, etc. will pervade the halls and upper rooms.

295. The ventilation of the cellar is a matter of great importance to the health of the family, yet in the majority of dwellings no provision is made for it, and it is not even supposed to be necessary.

The necessary ventilation can be secured by running a flue from the highest point in the cellar, usually the top of the stairway, up to the roof, placing it in some interior wall where it will be reasonably warm. The proper size for this flue depends upon the character of the cellar-whether wet or dry-and the nature and quantity of materials stored in it. Ventilation is needed most when the place is both warm and moist, because fermentation then proceeds with the greatest freedom, and molds and fungi flourish vigorously. It is not advisable to merely make an opening into one of the chimneys for ventilating purposes, because it will probably spoil the draft of the stove or heating apparatus connected to it.

The presence of a furnace or boiler in a cellar helps to ventilate it, by passing a considerable quantity of air through the fire and up the chimney. The quantity thus removed, however, is quite insufficient unless the cellar be small, very clean, and unusually dry.

296. The first floor in a dwelling should be made gas-tight, in order to prevent the cellar air from passing through and mingling with the air in the living rooms. This is best done by laying the floor in two thicknesses, with a thick layer of tarred paper between them. Ordinary building paper is quite inferior to the tarred material for this purpose. This floor should extend to the outer walls of the building and be made air-tight around the edges, so that no air can possibly pass up from the cellar into the spaces between the studding or furring strips.

In the cheaper class of frame dwellings, it is a common practice to leave these spaces open, so that they form flues, up which the cellar air passes to the attic without restriction. The ventilation thus afforded, although quite unintentional, has probably saved the inmates of such dwellings, in a multitude of cases, from the sickening effects of bad cellars that otherwise would have been deadly. The existence of these flues or passages is highly objectionable on another account, namely, that they permit heat to escape through the walls with undue rapidity. All circulation of air within them should be prevented, either by putting in tight horizontal partitions at short intervals, or, better still, by filling the spaces with mineral wool or other non-conducting materials. Brick and mortar are not desirable for this purpose, because they absorb a great deal of moisture, and tend to rot the woodwork.