Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: FRESH AIR INLET. What is a fresh air inlet and what is its use? The fresh air inlet is a line of pipe run from the house side of the main trap and opening into the outer air. The use of this pipe is to prevent air lock between the fixture traps and the main trap, to bring into the system a supply of fresh air, and to aid in creating a circulation of this air through the plumbing system. What should be the size of the fresh air inlet? It should never be less than four inches when the main soil pipe is four inches. In most cases this size is large enough even though the main pipe is larger. Why would it be wrong to take the fresh air inlet from the sewer side of the trap? Because it would not only fail to prevent air lock but would not create a circulation of air through the system, and would vent the sewer in a dangerous place. Where should the fresh air inlet enter the building? Through the cellar wall at a point as far removed as possible from windows, doors, and cold air box to the furnace. How far should the outer end of the fresh air inlet be carried from any door, window, or furnace box? Fifteen or twenty feet if possible. This frequently necessitates running out into the yard or lawn before coming up through the ground. Is the fresh air inlet used on systems having no main trap? It is not, for the reason that in such a case there is a circulation from the sewer through the roof, and no danger of air lock. Moreover, if used on systems having no main trap, it would ventilate the sewer in a dangerous place. Should drainage ever be entered into the fresh air inlet? Never. What effect does the fresh air inlet have upon the evaporation and cooling of the main trap seal? By bringing in air upon the seal it increases evaporation and ten...