UL 1738 STANDARD FOR SAFETY Venting Systems for Gas-BurningAppliances, Categories ll, Ill, and lV
1 Scope
1.1These requirements cover venting systems intended for venting Category lI, ll, or lV gas-burningappliances as defined by the Standard for Gas-Fired Central Furnaces (except Direct-Vent CentralFurnaces),ANSI Z21.47 and the National Fuel Gas Code，NFPA 54. Venting systems covered by theserequirements are intended to be used with Category l ll, and V appliances that have been installed inaccordance with NFPA 54, and with codes such as the BOCA National Mechanical Code, the StandardMechanical Code, the Uniform Mechanical Code, and local codes.
1.2 A product that contains features, characteristics, components, materials, or systems new or differentfrom those covered by the requirements in this standard, and that involves a risk of fire or of electric shockor injury to persons shall be evaluated using appropriate additional component and end-productrequirements to maintain the level of safety as originally anticipated by the intent of this standard.Aproduct whose features，characteristics，components，materials，or systems conflict with specificrequirements or provisions of this standard does not comply with this standard.Revision of requirementsshall be proposed and adopted in conformance with the methods employed for development, revision, andimplementation of this standard.
2Units of Measurement
2.1Values stated without parentheses are the requirement. Values in parentheses are explanatory orapproximate information.
3Glossary
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 nationallyrecognized standards, as appropriate.
3.3 APPLIANCE ADAPTER- A special gas vent fitting which typically joins non-metallic vent systems tothe outlet of a fuel gas-burning appliance.
3.4 CATEGORY II APPLIANCE-An appliance that operates with a nonpositive vent static pressure andwith 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.
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