IO137 32
22. Listed, corrugated metallic chimney liner
systems in masonry chimneys shall be
sized by using tables 3 or 4 for common
venting with the maximum capacity re-
duced by 20% (0.80 X maximum capacity)
and the minimum capacity shown in the
applicable table. Corrugated metal vent
systems installed with bends or offsets
require additional reduction of the vent
maximum capacity (See note 6).
23. For multiple units of gas utilization equip-
ment all located on one floor, available to-
tal height “H” is measured from the high-
est draft hood outlet or flue collar up to the
level of the cap or terminal. Connector
rise “R” is taken from the measured outlet
or flue collar to the level where the vent
gas streams come together. (Not applica-
ble for multi-story).
24. For multi-story installations, available total
height for each segment of the system “H”
is the vertical distance between the draft
hood outlet or flue collar entering that
segment and the centerline of the next
higher interconnection tee (See Figure
13).
25. The size of the lowest connector and of
the vertical vent leading to the lowest in-
terconnection of a multi-story system must
be according to table 1 or 2, for available
total height “H” up to the lowers connec-
tion (See figure 14).
26. Common vents in multi-story systems
should be type B and have no offsets.
27. Numbers followed by an asterisk(*) in Table
5 & 6, indicate the possibility of continuous
condensation, depending upon locality.
Consult appliance manufacturer, local serv-
ing gas supplier, and/or authority having juris-
diction.
28. In a single run of vent or vent connector,
more than one diameter and type of pipe
are permitted to be used, provided that all
the sizes are permitted by the tables.
29. If the desired vent height and connector
rise and/or lateral are between the table
entries, linear interpolation is permitted for
calculation of the permissible appliance
input ratings. Extrapolation beyond the ta-
ble entries is not recommended.
30. All combinations of pipe sizes, single wall,
and double wall metal pipe are allowed
within any connector run(s) or within the
common vent provided ALL of the appro-
priate tables permit All of the desired sizes
and type of pipe, as if they were used for
the entire length of the subject connector
vent. If a single wall and type B double wall
pipe are used for vent connectors, the
common vent must be sized using table 4.
31. Locate the draft hood outlet or flue collar of
the smallest input appliance closest to or
under the common vent.
32. When the vent table permits more than one
diameter of pipe to be used for a connec-
tor or vent, the smallest permitted diame-
ter should be preferred.
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