The sanitary rooms of a building are those in which the foulest portions of the domestic and personal duties are performed, and yet less care is often bestowed on the ventilation of these rooms than of any other rooms in the house. In many towns the by-laws specifiy that an air-grate must be fixed in the external wall of every water-closet"; sometimes two are demanded, one near the floor and the other near the ceiling, the assumption being that the latter will act as an outlet and the former as an inlet. Unfortunately, this assumption is often proved to be erroneous, as both grates frequently act as inlets. The value of these air-grates has been much overrated. As a rule they serve as inlets, and if, as is generally the case, the rooms have no extract-shafts, the air, mixed perhaps with the foul air from the sanitary fittings, is drawn into the adjacent living rooms or bedrooms, whence it escapes by means of the fireplace flues. In other words, the "fresh-air" supply of the house is to a large extent obtained through the bathroom and water-closet. The air-grates have also the disadvantage of reducing the temperature of the rooms in winter and of increasing the risk of frozen pipes.

If proper extract-shafts are provided from these rooms there will be little danger of vitiated air being drawn into the rest of the building; the current of air will be in the opposite direction, i.e., from the main building to the sanitary room. In the scullery, bathroom, etc, the extractshaft may take the form of an open fireplace or of a flue formed in the chimney-breast by the side of the smoke-flue. These flues ought to be formed with fireclay tubes, thoroughly grouted around, so that the foul air cannot escape into the rooms above. In the water-closet, housemaid's closet, etc, it may be a flue of the kind just described, or a special sheet-metal shaft leading to an extracting cowl fixed on the roof.

A clever contrivance for ventilating water-closets and other rooms in which flushing cisterns are placed has been designed by Messrs. Kerrill & Hunter. It consists of a fan actuated by the water as it flows into the cistern. Consequently, every time the cistern is used the fan is automatically started and continues to run until the cistern is full again. The fan is said to be capable of extracting 200 cubic ft. of air per minute with a 60-lb. pressure of water. This contrivance will be of service in many cases where extract-flues cannot well be provided; it has the disadvantage of being spasmodic in its action, but this disadvantage is not very serious if the sanitary fittings and plumbing are such as to exclude all drain-air from the room.

Ranges of water-closets and urinals in clubs, hotels, and public buildings, cannot, in many cases, be properly ventilated except by mechanical means. An effective arrangement consists in fixing an extract fan in the ceiling of a small chamber conveniently placed with regard to the closets (that is to say, in the middle of a long range, or, in the angle formed by ranges on two sides of the room), and by carrying up from the fan an extract shaft to the top of the building. From each closet a horizontal shaft is carried under the ceiling to this chamber, so that the air from all the closets is extracted by the single fan. As a rule the urinals are placed in the room from which the closets are entered, and if suitable openings are made between this room and the closets, the urinals will also be properly ventilated. The fan may be driven by electricity or water, or in some other way, but as a rule an electric fan will be the most convenient.