This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
A local vent is a pipe connected directly with a closet or urinal for carrying off any odor when in use. It has no connection with the soil pipe, unless the trap seal becomes broken, and is not provided for the purpose of carrying off gases from the sewer. A urinal provided with a local vent is shown in Fig. 73.
Sometimes a small register face back of the fixture, and connecting with a flue in the wall, is used in place of the regular local vent. In order for a vent flue of either form to be of any value, it must he warmed to insure a proper circulation of air through it. This is done in some cases by placing a gas-jet at the bottom of the flue, in others a steam or hot water pipe is run through a portion of the flue, and in still others the vent is carried up beside a chimney flue, from which it may receive sufficient warmth to assist the circulation to some extent.