February 9, 2023
From the 2021 UPC Illustrated Training Manual, Chapter 5, WATER HEATERS
510.1.10 Chimney and Vent Locations. Table 510.1.2(1) through Table 510.1.2(5) shall be used only for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Table 509.6.1, and where vents terminate in accordance with Section 509.6.1(1)(b), the outdoor portion of the vent shall be enclosed as required by this paragraph for vents not considered to be exposed to the outdoors, or such venting system shall be engineered. A Type B vent passing through an unventilated enclosure or chase insulated to a value of not less than R-8 shall not be considered to be exposed to the outdoors. Table 510.1.2(3) in combination with Table 510.1.2(6) shall be used for claytile-lined exterior masonry chimneys, provided all of the following requirements are met:
(1) The vent connector is Type B double wall.
(2) The vent connector length is limited to 18 inches per inch (18 mm/mm) of vent connector diameter.
(3) The appliance is draft hood equipped.
(4) The input rating is less than the maximum capacity given in Table 510.1.2(3).
(5) For a water heater, the outdoor design temperature shall not be less than 5°F (-15°C).
(6) For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 510.1.2(6). [NFPA 54:13.1.11]
This section specifies which tables to use when sizing chimneys and vents not exposed to the outdoors below the roof line. Special attention is paid to Type B vents or listed chimney lining systems passing through a masonry chimney flu or a chase insulated to a value of at least R8. Such installations are not considered as being exposed to the outdoors (see Figure 510.1.10a).
When sizing a clay-tile-lined exterior masonry chimney, Table 510.1.2(3) in combination with Table 510.1.2(6) shall be used, provided the six conditions are met. To size chimneys and vents serving only water heaters, the outdoor design temperature must be greater than 5˚F. See Figure 510.1.10 for a map of the United States showing the temperature zones. In colder climates, either the chimney must be lined with a metallic liner or another vent must be used. To size chimneys and vents serving space heating appliances, Table 510.1.2(6) for the minimum capacity and Table 510.1.2(3) for the maximum vent capacity will be used.
Note that only Type B vent connectors are allowed to minimize heat loss through vent connectors. Water heaters are treated differently from heating appliances because their total operating hours are not sufficient to keep a chimney warm in cold periods, resulting in condensation of water in the chimney vent.
The 2021 Uniform Plumbing Code Illustrated Training Manual is available for purchase here.
(This is not to be considered the official position of IAPMO, nor is it an official interpretation of the Codes.)
© 2023 International Association of Plumbing and Mechanical Officials.
Last modified: February 9, 2023