UL-1738-2021 pdf download – Venting Systems for Gas-Burning Appliances, Categories II, III, and IV .
10 Thimbles 10.1 A venting system intended for horizontal installation shall be provided with a thimble constructed to enable the venting system to penetrate a vertical wall unless the venting system is tested at zero clearance to combustible construction. 10.2 A thimble shall have sufficient strength and bearing surface to maintain the required clearance from the venting system parts to the wall studs and inner surfaces of walls. 10.3 Thimbles for non-metallic venting systems shall be provided and designed to permit unrestricted longitudal or radial thermal expansion and contraction movement that occurs during pipe heating. 11 Support Assembly 11.1 A support assembly, if required, shall establish and maintain the minimum required clearance between a venting system and combustible construction. A support for installation in a joist area shall constitute a complete firestop when tested in accordance with these requirements. 11.2 A support assembly shall sustain a load equivalent to four times the weight imposed upon it by all the venting system parts it is intended to support. See Vertical Support Test, Section 21. 11.3 A support assembly intended to be secured by nails or screws shall be arranged so that the load on such holding means will be a shear or compressive load. 11.4 A venting system intended for exterior installation shall be provided with support assemblies. 11.5 An offset vent shall be supported at or immediately above the vertical return elbow at the first floor or roof above the offset section. 11.6 An exterior support assembly shall be constructed to maintain specified clearances to adjacent combustible construction. 11.7 Supports and hangers shall be specified and shall accommodate both longitudinal and lateral vent movement. Instructions for the maximum length of pipe between supports and hangers shall be specified in the manufacturer’s installation instructions.
13 Vent Termination or Caps 13.1 A vent termination or cap shall be provided to resist the entrance of debris and rain into the vent gas conduit and into any cooling air passage terminating exterior to the building. See Rain Test, Section 24. 13.2 A vent termination or cap shall be constructed so that snow, leaves, and debris falling or blown onto it are not retained so as to obstruct vent gas or cooling air passages. 14 Drain Fittings 14.1 Drain fittings, if provided, shall be permanently marked at or near the fitting as specified in 45.8. The marking shall advise the user to ascertain that the appliance is intended for use with a vent system that includes a drain fitting. 15 Appliance Adapters 15.1 Appliance adapters shall be provided as part of a non-metallic gas vent pipe system intended for category III appliances. The adapter shall be provided with identification of the intended uses of the adapter.