IO137 30
ity must be reduced by 20% (0.80 X
maximum vent capacity).
b) The minimum capacity (FAN MIN.) shall
be determined by referring to the corre-
sponding single appliance table (tables 1
& 2). In this case, for each appliance the
entire vent connector and common vent
from the appliance to the vent termina-
tion would be treated as a single appli-
ance vent, as if the other appliances
were not present.
5. If vent connectors are combined prior to
entering the common vent, the maximum
common vent capacity listed in the com-
mon vent tables must be reduced by 10%,
the equivalent of one (1) 90
o
elbow. `See
figure 7. The horizontal length of the com-
mon vent connector or manifold (L) should
not exceed 1 1/2 feet (18 inches) for each
inch of common vent diameter.
6. If the common vent is offset as shown in
figure 8, the maximum common vent ca-
pacity listed in the common venting tables
should be reduced by 20%, the equivalent
of two (2) 90° elbows. The horizontal
length of the offset shall not exceed 1 1/2
feet for each inch of common vent diame-
ter.
7. The common vent diameter must always be
at least as large as the largest vent connec-
tor diameter. All interconnection fittings
must also be the same size as the com-
mon vent.
8. Type B gas vents shall terminate above the
roof surface with a listed cap or listed roof
assembly according to their respective list-
ing and the vent manufacture’s instructions.
VENT CAPS 12” AND SMALLER
Listed gas venting systems using
listed vent caps 12” and smaller may
terminate according to the VENT
TERMINATION TABLE. (See figure 1)
MINIMUM
HEIGHT
8’ MIN.
X
12
LOWEST
DISCHARGE
OPENING
LISTED
CAP
VERTICAL
WALL
THE VENT TERMINATION SHOULD NOT BE
LESS THAN 8 FT. FROM A VERTICAL WALL
FIGURE 1 -VENT CAPS 12” OR SMALLER
GAS VENT TERMINATION TABLE
ROOF PITCH MINIMUM HEIGHT
FLAT T0 to 7 / 12 1.0 FEET *
OVER 7 / 12 TO 8 / 12 1.5 FEET
OVER 8 / 12 TO 9 / 12 2.0 FEET
OVER 9 / 12 TO 10 / 12 2.5 FEET
OVER 10 / 12 TO 11 / 12 3.25 FEET
OVER 11 / 12 TO 12 / 12 4.0 FEET
OVER 12 / 12 TO 14 / 12 5.0 FEET
OVER 14 / 12 TO 16 / 12 6.0 FEET
OVER 16 / 12 TO 18 / 12 7.0 FEET
OVER 18 / 12 TO 20 / 12 7.5 FEET
OVER 20 / 12 TO 21 / 12 8.0 FEET
* This requirement covers most installations
9. Use sea level input rating when determining
maximum capacity for high altitude installa-
tion. Use actual input rating for determining
minimum capacity for high altitude installa-
tion.
10. No portion of the vent system can extend
into, or pass through any circulating air
duct or plenum.
11. All vent pipe passing through floors, walls
and ceilings must be installed with the listed
clearance to combustible materials and be
fire stopped according to local codes. In
the absence of local codes refer to NFGC
(Z223.1).
12. Vent connectors serving Category I appli-
ances shall not be connected to any por-
tion of mechanical draft systems operation
under positive pressure such as Category
III or IV Venting Systems.
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