A local or surface vent is a vent provided for the purpose of carrying off foul odors incident to the use of the water closet.

This pipe is also applied to the urinal and slop sink to good advantage. The local vent has no relation whatever to the drainage system or. to the back-venting system, and may be considered as a measure looking to the comfort of the people making use of the fixtures to which it is applied, rather than as a strictly sanitary measure.

Local ventilation differs in no way from any other form of ventilation.

Plate XVIII. Local Venting

Local Venting Plate 18.

of Water Closets

Local Venting 66

The system generally in use consists in connecting a pipe from the local vent spud on the water-closet bowl to a heated flue. A good feature of this form of ventilation is that it is accomplished without any expense of operation. As long as a sufficient difference in temperature between the air of the toilet room and the air of the flue exists, excellent results may be maintained by means of this system.

The heated air of the flue being lighter because of being expanded by the heat, rises through the flue, the tendency being to produce a vacuum behind the column of constantly rising hot air. A suction is thus caused on the air in the pipe connecting to the rim of the water closet, and this air is drawn into the flue and forced up and out of it by the current of heated air. The suction is often so strong that small pieces of paper thrown into the water-closet bowl will be forcibly drawn into the local vent pipe and into the flue. The only point against this form of ventilation is the fact that it cannot always be connected to a flue which is heated throughout the year. It is a form of vent which is used principally in dwellings, tenement houses, and other buildings in which the flue to which the local vents are connected is not likely to be heated during the warm months.

On larger work, such as public toilet rooms, other means are used for obtaining ventilation.

However, in most cases where the local vent is applied, no other ventilation would probably be made use of because of the expense of running the mechanical devices used in producing it, and it would therefore seem of much advantage to the inmates to be able to enjoy its comforts during those months when the flues are heated. There is this to be said concerning the months of the year when it might not produce results: the windows at such season of the year are generally wide open, and the need of artificial ventilation not so great as during the period when the local vent does its work thoroughly.

It is certainly true that the toilet room provided with the local vent is far more wholesome than the one which is without it. This vent, sometimes called a seat vent, opens into the water-closet bowl just back of and below the seat, and while the water closet is in use carries off all the odors incident to its use. In addition, when the cover of the closet is down, there is sufficient space for air to enter the bowl and pass into the vent between the seat and the crockery, which are kept apart by means of rubber bumpers on the seat. Therefore the local vent is at all times providing ventilation not only for the water closet itself, but for the entire toilet room.

In order to provide proper ventilation three factors are necessary. There must be an inward passage of fresh air and outward passage of foul air, and a force acting to produce the movement of air which results in the changing of the air. The first factor named is one most likely to be omitted in providing a system of ventilation. Foul air will not pass out of the toilet room unless other air is brought in to take its place. The demand for a supply of fresh air is very largely filled by natural means. Open windows, the entrance of air through window casings, etc., supply in general a considerable amount of fresh air. In addition, it is a fact that air passes through brick walls to a very considerable extent, and through the plastering as well.

Many plumbing ordinances do not make the use of local ventilation compulsory. Even though it is not compulsory to use the local vent in all toilet rooms, there are certain conditions under which it certainly should be used as a sanitary precaution.

In this connection the following requirement is a good one:

All water closets, slop sinks, and urinals should be provided with local vents when located in rooms which receive their light from light shafts, skylights, or courtyards, or when located in compartments not directly connected with the outside atmosphere and sunlight. The application of the local vent may be made more universal by providing artificial means of creating a draft when it is impossible to enter a heated flue or a flue which is always heated. Under such conditions an excellent method is to carry the local vents up to an airtight box or compartment heated by means of gas jets, the pipe from which should be carried 3 ft. or more above the roof, ending in an automatic ventilator. Another method of a similar nature is to provide a specially constructed device of the kind shown in Fig. C, Plate 18. This may be inserted in the main vertical line of local vent, and will be found to perform excellent service at only a slight cost for the consumption of gas.

Figs. A and B of Plate 18 show two different systems of local venting. Fig. A gives the separate system of vents, in which the vent from each water closet is carried separately to the point where entrance is made into the heated flue.

The system shown in Fig. B consists of a main vertical line, into which the local vent from each water closet is entered, and is probably more commonly in use than the system first mentioned. The system of separate vents of Fig. A has very decided advantages over the other system.