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Finned copper tube gas boilers & water heaters – Boiler Manual
6
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DIRECT VENT, POSITIVE PRESSURE,
CATEGORY IV
In this confi guration the boiler/water heater blower is used
to push the fl ue products to the outdoors while drawing combustion
air from the outdoors. Th e Intake Air Option instructions under
the “COMBUSTION AIR & VENTILATION” section must be
followed! Th e vent system must be sized per Table 4.
Table 4
Category IV
Model
Size
Pipe Diameter (Min.)
(Up to 60’)
in
mm
500
5
127
750
5
127
1000
6
152
1250
6
152
1500
8
203
1750
10
254
2000
10
254
Horizontal Direct Vent Systems
Figures 1 & 2
Th e vent materials used in horizontal vent systems must be certifi ed
to UL 1738 for installations in the United States, ULC S636 for
installations in Canada. Th e certifi ed vent terminal from RBI must
also be used.
Th e maximum equivalent length for the horizontal vent pipe is
60 ft
,
18.3 m
.
Each 90° elbow and the vent terminal are equal to
10 linear ft
,
3.0 m
of pipe. If any part of a single wall metal vent
system passes through an unheated space, it must be insulated with
insulation rated for
400°F
,
204°C
. Structrual penetrations must
be made using approved fi re-stops. For best results, horizontal vent
systems should be as short and straight as possible.
Th e vent system must be both gas tight and watertight. All seams
and joints in metal pipes must be joined and sealed in accordance
with the vent system manufacturer’s instructions.
When horizontal vent runs exceed
5 ft
,
1.5 m
they must be supported
at
3 ft
,
0.9 m
intervals with overhead hangers. Th e vent system
must be pitched down, toward the vent terminal,
1/4 in/ft
,
20 mm/m.
If any part of a single wall metal vent system passes through an
unheated space it must be insulated with insulation rated for
400°F
,
204°C
.
Horizontal vent systems shall terminate at least
4 ft
,
1.2 m
below,
4 ft
,
1.2 m
horizontally from or
1 ft
,
0.30 m
above any door, window
or gravity air inlet into any building. It must not terminate less than
4 ft
,
1.2 m
horizontally from, and in no case above or below, unless
a
4 ft
,
1.2 m
horizontal distance is maintained, from electric meters,
gas meters, regulators and relief equipment and not less than
7 ft
,
2.1 m
above adjacent public walkway. Th e bott om of the vent
terminal(s) shall be located at least
5 ft
,
1.5 m
above the air intake
terminal(s) unless there is a minimum
5 ft
,
1.5 m
horizontal
separation between them. Avoid terminal locations likely to be
aff ected by winds, snowdrift s, people and pets. Protect building
materials and vegetation from degradation caused by the fl ue gases.
Vertical Direct Vent Systems – Figure 3
If any part of a single wall metal vent system passes through an
unheated space, it must be insulated with insulation rated for
400°F
,
204°C
. Structural penetrations must be made using approved fi re-
stops.
An approved, nonrestrictive vent terminal must be used Th e top
of a vertical vent system must extend at least
5
1
/
2
ft
,
1.7 m
above
the roof surface and maximum snow line that it passes through,
4 ft
,
1.2 m
above the intake air terminal, see Figure 3.
In addition the vent system must conform to the dimensions shown
in Figure 3. Th e penetration point in the roof must be properly
fl ashed and sealed.
Th e vent system must be gas tight. All seams and joints in metal
pipes must be joined and sealed in accordance with the vent system
manufacturer’s instructions.
Combination Direct Vent Systems – Figure 4
Th e boiler/water heater can be vented vertically with the intake
air piped horizontally through an outside wall. Follow the instruct-
ions in the Intake Air Option – Horizontal Guidelines on page
5. Also follow the general instructions in the “COMBUSTION
AIR & VENTILATION” and “GENERA
L VENTING GUIDE-
LINES” sections.
