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 803.2(1), provided the following apply:
The 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. (See Figure 802.6.4.2)
The size of the connector for a segment is determined
from the appliance's gas input rate and
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, shall be based on the total appliance's gas input rate entering that segment and its total
height. [NFPA 54:12.7.4.3]
FIGURE 802.6.4.2 USE OF MANIFOLDED COMMON VENT CONNECTOR
[NFPA 54: FIGURE F.1(k)]
gas ventsystem listed for a single story shall be installed in single-story
buildings or the top story of multistory buildings.
Vented wall furnaces ...
of multistory buildings.
Vented wall furnaces connected to a Type B-W gas ventsystem listed for installation in multistory buildings shall
be permitted ...
