504.3.1 Vent obstructions.
FGC § 504.3.1
These venting tables shall not be used where obstructions, as described in Section 503.15, are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer's instructions or in accordance with the following: 1. The maximum capacity of the vent connector shall be determined using the NAT Max column.
2.The maximum capacity of the vertical vent or chimney shall be determined using the FAN + NAT column when the second appliance is a fan-assisted appliance, or the NAT + NAT column when the second appliance is equipped with a draft hood.
3.The minimum capacity shall be determined as if the appliance were a fan-assisted appliance. 3.1. The minimum capacity of the vent connector shall be determined using the FAN Min column. 3.2. The FAN + FAN column shall be used where the second appliance is a fan-assisted appliance, and the FAN + NAT column shall be used where the second appliance is equipped with a draft hood, to determine whether the vertical vent or chimney configuration is not permitted (NA). Where the vent configuration is NA, the vent configuration shall not be permitted and an alternative venting configuration shall be utilized.
