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509.6.3.2 Multistory Venting System
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The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 510.2(1), provided all of the following apply:
- The available total height (H) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee.
- The size of the connector for a segment is determined from the appliance's gas input rate and available connector rise, and shall not be smaller than the draft hood outlet or flue collar size.
- The size of the common vertical vent segment, and of the interconnection tee at the base of that segment, is based on the total appliance's gas input rate entering that segment and its available total height. [NFPA 54:18.104.22.168]