151. When a water closet is being used, an offensive smell is usually given off. This is partly taken away by the local vent (if any), and part of it will contaminate the air in the apartment. To remove the odor from the apartment, it is necessary to remove all the air in the apartment. The frequency with which the air in the apartment should be renewed will depend upon how often the closet is used. The air may be changed in various ways. The most common way is to simply open a window at top and bottom. This causes a circulation between the water-closet apartment and the outer atmosphere. This method of changing the air, however, is only suitable for mild weather.

A 4 or 6 inch bright tin or galvanized-iron pipe should be run from the ceiling just over the water closet or near it, to above the roof, where its orifice should be guarded by a properly designed ventilator cap or cowl. The orifice of the tube above the closet should be funnel mouthed to 12 or 14 inches in diameter.

The tube should, if possible, be run up alongside a hot chimney flue, so that the air within it may be rarified, and cause an upward draft. Advantage should be taken of the heat from burning gas jets in the apartment to facilitate the draft. This can be done by placing the light immediately under the funnel-mouthed inlet to the tube.

Dark water-closet apartments should in all cases be thoroughly ventilated, preferably, as explained above, by a tube with a gas jet burning within it or under it. The velocity with which the air travels up the tube will vary with the difference between the mean temperature of the air in the tube and the temperature of the outer atmosphere, also with the length of the tube and the number of bends, etc. in its length. In order to have the least resistance to the upward flow of the foul air, the pipe should be round or square in section, and should have as few elbows as possible.

When an exit is provided for foul air in the closet apartment, provision must also be made for an inlet of fresh air.

This is best done by having a space of 2 or 3 inches between the bottom of the door and the floor.

152. Latrines, or a number of single water closets in the same general apartment, are usually ventilated by one large ventilating tube run from the ceiling of the apartment. The closets are placed side by side with a 6 or 7 foot partition between. The door of each closet, being hinged about 6 inches above the floor, forms the fresh air-inlet for the small space enclosed. The foul air rising upwards discharges into the upper parts of the general apartment, and soon passes out through the ventilator.