UL 1738:2021 pdf download.STANDARD FOR SAFETY-Venting Systems for Gas-Burning Appliances, Categories II,III, and IV.
1.1 These requirements cover venting systems intended for venting Category II, III, or IV gas-burning appliances as defined by the Standard for Gas-Fired Central Furnaces (except Direct-Vent Central Furnaces), ANSI Z21.47 and the National Fuel Gas Code, NFPA 54. Venting systems covered by these requirements are intended to be used with Category II, Ill, and IV appliances that have been installed in accordance with NFPA 54, and with codes such as the BOCA National Mechanical Code, the Standard Mechanical Code, the Uniform Mechanical Code, and local codes.
1.2 A product that contains features, characteristics, components, materials, or systems new or different from those covered by the requirements in this standard, and that involves a risk of fire or of electric shock or injury to persons shall be evaluated using appropriate additional component and end-product requirements to maintain the level of safety as originally anticipated by the intent of this standard. A product whose features, characteristics, components, materials, or systems conflict with specific requirements or provisions of this standard does not comply with this standard. Revision of requirements shall be proposed and adopted in conformance with the methods employed for development, revision, and implementation of this standard.
2 Units of Measurement
2.1 Values stated without parentheses are the requirement. Values in parentheses are explanatory or
approximate information.
3 Glossary
3.1 For the purpose of these requirements, the following definitions apply.
3.2 APPLIANCE — A gas burning device constructed and installed in accordance with nationally recognized standards, as appropriate.
3.3 APPLIANCE ADAPTER — A special gas vent fitting which typically joins non-metallic vent systems to the outlet of a fuel gas-burning appliance.
3.4 CATEGORY II APPLIANCE — An appliance that operates with a nonpositive vent static pressure and with a flue loss less than 17 percent in accordance with the Standard for Gas-Fired Central Furnaces (except Direct-Vent Central Furnaces), ANSI Z21 .47.
3.5 CATEGORY Ill APPLIANCE — An appliance that operates with a positive vent static pressure and with a flue loss not less than 17 percent in accordance with the Standard for Gas-Fired Central Furnaces (except Direct-Vent Central Furnaces), ANSI Z21 .47.
3.6 CATEGORY IV APPLIANCE — An appliance that operates with a positive vent static pressure and with a flue loss less than 17 percent in accordance with the Standard for Gas-Fired Central Furnaces (except Direct-Vent Central Furnaces), ANSI Z21 .47.
3.7 COMBUSTIBLE MATERIAL — Material made of or surfaced with wood, compressed paper, plant fibers, or other material that will ignite and burn, as applied to materials adjacent to or in contact with heatproducing appliances, chimney connectors and vent connectors, steam and hot water pipes, and warm air ducts. Such material shall be considered as combustible even though flameproofed, fire-retardant treated, or plastered.UL 1738 pdf download.