March 19, 2026
From the 2024 UPC Illustrated Training Manual, Chapter 5 – WATER HEATERS
509.5.10 Space Surrounding Lining or Vent. The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appliance.
Exception: The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions. [NFPA 54:12.6.8.1]
The use of a masonry chimney as a chase for vents is a practical solution to an existing unlined, oversized or failed chimney. When installing vents in a chimney space, the manufacturer’s installation requirements for all of the vent material must be followed. If required by the vent manufacturer, penetrating the masonry chimney to install supports might be necessary.
When using an abandoned chimney as a chase for multiple vents, care should be taken to ensure that the vent materials are compatible and that vent failure does not result inadvertently. Category I or III gas appliance vent gas temperatures can exceed 300°F (150°C). Contact between the high-temperature Category I or III vent material and the PVC vent pipe can cause the PVC pipe to degrade or soften to the extent of failure. With the chimney opening sealed around the vent pipes, the products of combustion, which can escape from the failed PVC pipe, will be trapped in the chimney. These gases could eventually leak back into the living space or corrode the other nearby vents.
From the 2024 UMC Illustrated Training Manual, Chapter 13 – FUEL GAS PIPING
1308.3.3 Allowable Pressure Drop. The design pressure loss in a piping system from the point of delivery to the inlet connection of all appliances served shall be such that the supply pressure at each appliance inlet is greater than or equal to the minimum pressure required by the appliance. [NFPA 54:5.3.4]
Gas-piping systems must supply the volume of gas required by each appliance at a pressure within the design range established by the appliance manufacturer. The sizing tables take pressure loss into consideration and most systems will fall within the pressure loss values of the tables. If the system does not fall within the range of the tables, then engineered calculations must be used or the use of a higher inlet pressure should be considered.
The gas inlet pressure to the connected equipment must also remain within the manufacturer’s design limits when the equipment “cycles off.” Gas-piping systems that operate at pressures exceeding the connected gas appliance’s rated inlet pressure or that deliver gas at a pressure that varies outside the equipment manufacturer’s design inlet pressure limits must incorporate pressure regulators into the system so that gas delivered to the equipment will be within the design pressure range of the appliance.
(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: March 18, 2026