January 30, 2025
From the 2024 UPC Illustrated Training Manual, Chapter 7 – SANITARY DRAINAGE
706.4 Vertical to Horizontal. Vertical drainage lines connecting with horizontal drainage lines shall enter through 45 degree (0.79 rad) wye branches, combination wye and one-eighth bend branches, or other approved fittings of equivalent sweep. Branches or offsets of 60 degrees (1.05 rad) shall be permitted to be used where installed in a true vertical position.
One of the most critical changes of direction from vertical to horizontal flows in the drainage system is at the base of a stack. As the vertical flow makes a forced entry into a horizontal pipe, the flow becomes violently turbulent and abruptly increases in depth downstream the vertical stack causing what is called a “hydraulic jump” (see also commentary in Section 901.2). This jump can cause backpressures upstream of the jump and affect trap seals in close proximity to the base of the stack. The proper transitional fitting with the proper sweep will reduce the affect of the hydraulic jump on the system. These fittings will be with 45-degree angles (wyes and combination wye and one-eighth bend) or sweeps (long and short). The short sweep fitting is not to be confused with a quarter bend fitting, which has a short ninety-degree radial bend. The short sweep radius approximates the radius of two one eighth bends put together.
From the 2024 UMC Illustrated Training Manual, Chapter 8 – CHIMNEYS AND VENTS
802.7.1 Cold Climate. Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99 percent winter design temperature is below 32°F (0°C). [NFPA 54:12.8.2]
The outdoor use of single-wall metal pipe in cold climates is restricted by Section 802.7.1 to prevent premature corrosion of the vent. In cold climates, the low ambient temperature can cool vent gases to the point at which water vapor condenses in the vent and causes corrosion. The code does not attempt to define a “cold climate” because the particular installation and local conditions often determine the acceptability of using single-wall metal pipe. One simple guideline is checking to see how often the replacement of single-wall metal pipe is required in the area in question. Table 803.2(7) and Table 803.2(9) quantify the effects of cold ambient temperatures on masonry chimneys. They cannot be used for single-wall metal pipe.
(This is not to be considered the official position of IAPMO, nor is it an official interpretation of the Codes.)
IAPMO
IAPMO develops and publishes the Uniform Plumbing Code®,the most widely recognized code of practice used by the plumbing industry worldwide; Uniform Mechanical Code®; Uniform Swimming Pool, Spa and Hot Tub Code®; and Uniform Solar Energy, Hydronics and Geothermal Code™ — the only plumbing, mechanical, solar energy and swimming pool codes designated by ANSI as American National Standards — and the Water Efficiency Standard (WE-Stand)™. IAPMO works with government, contractors, labor force, and manufacturers to produce product standards, technical manuals, personnel certification/educational programs and additional resources in order to meet the ever-evolving demands of the industry in protecting public health and safety.
Last modified: January 30, 2025