December 5, 2025
From the 2024 UPC Illustrated Training Manual, Chapter 9, VENTS
905.6 Common Vertical Pipe. Two fixtures shall be permitted to be served by a common vertical pipe where each such fixture wastes separately into an approved double fitting having inlet openings at the same level.
Fixtures may be set back-to-back or side by side and use a common vent sized by combining the drainage fixture units of both fixtures to obtain the correct vent pipe size. The fitting used must be a double fixture fitting (see Figure 905.6). The double fixture fitting provides an opening that directs the flow from the two trap arms down the fixture drain. A double sanitary tee does not have this feature and could allow the effluent from one fixture to flow into the trap arm of the other fixture. The double combination or double wye and one-eighth bend could not be used (except for water closets or similar fixtures) because the vent opening would be below the weir of the trap.
BACK-TO-BACK FIXTURES INSTALLED WITH DOUBLE FIXTURE FITTING
From the 2024 UMC Illustrated Training Manual, Chapter 9, INSTALLATION OF SPECIFIC APPLIANCES
911.2 Prohibited Installations. Decorative appliances for installation in vented fireplaces shall not be installed in bathrooms or bedrooms unless the bedroom or bathroom has the required volume in accordance with Section 701.4. [NFPA 54:10.6.2]
A decorative appliance is a “vented appliance” where the flames provide an aesthetic effect (see Section 224.0). A vented decorative appliance usually resembles a solid-fuel-burning fireplace in appearance. However, it is important to realize that it is a gas-burning appliance and is subject to all applicable installation standards. This type of appliance is usually not listed for use as a source of comfort heat.
Installation shall be prohibited in bathrooms or bedrooms unless listed for that purpose and if the room size complies with Section 701.4, Indoor Combustion Air, for required volume.
(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: December 4, 2025