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portions of the vent shall also be supported for the design
and weight of the material employed to maintain clearances
and to prevent physical damage or separation of joints.
NOTE: A vent adapter (field-supplied) may be required
to connect the Category IV vent to the heater.
Raypak strongly recommends routing and installing the
vent system prior to installing the water piping. Vent length
is critical and affects performance.
Termination
The vent terminal should be vertical and should terminate
outside the building at least 2 ft (610 mm) above the
highest point of the roof that is within 8 ft (2.4 m). The
vent cap should have a minimum clearance of 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) electric
meters, gas meters, regulators and relief equipment.
The distance of the vent terminal from adjacent public
walkways, adjacent buildings, open windows and building
openings must be consistent with the NFGC (U.S.) or
B149 (Canada). Gas vents supported only by flashing and
extended above the roof more than 5 ft (1.5 m) should
be securely guyed or braced to withstand snow and wind
loads.
A
CAUTION: A listed vent cap terminal suitable for
connection to the Cat IV vent materials, adequately
sized, must be used to evacuate the flue products from
the building.
VENT CAPS STACKED VERTICALLY
FLUE GASES MOVING IN PARALLEL
4'-0" (30.5 cm)
MIN. (TYP)
DISCHARGE
VENT CAPS ALL AT SAME ELEVATION
FLUE GASES MOVING TOWARD EACH OTHER
2" (51 mm) MIN. (TYP)
DISCHARGE
4'-0" (30.5 cm)
MIN. (TYP)
VENT CAPS AT STAGGERED ELEVATIONS
FLUE GASES MOVING TOWARD EACH OTHER
Figure 26. Sidewall Vent Cap Configurations
1" (25 mm)
MIN. (TYP)
1" (25 mm)
MIN. (TYP)
Common Venting
Raypak does not support common venting under positive-
pressure conditions.
Use an external variable-speed
extractor to draw the entire common vent to negative
pressure. See Figure 27. The NFGC does not address
sizing guidelines for the common venting of multiple
Category IV heaters. This is covered in the NFGC under
"Engineered Vent Systems". Table L provides boiler
discharge vent pressures at vent pressure switch and
volumes of flue products at full fire for the calculation of
appropriate vent and extractor sizing for common venting.
WARNING: Vent connectors serving any other
A
appliances shall not be connected into any portion of
mechanical draft systems operating under a positive
pressure. If an MVB heater is installed to replace an
existing heater, the vent system MUST be verified to
be of the correct size and of Category IV vent material
construction. If it is NOT, it MUST be replaced.
NOTE: For extractor sizing, typical CO2 levels are 9.0%
for natural gas and 10.2% for propane gas and flue
temperature of 300°F, at 100% firing rate. measured at
test port 12" above the flue collar.
Vent
Model
Size
Pressure
(in.)
(in. WC)
503A
753A
6
1003A
1253A
1503A
6
1753A
2003A
* NOTE: Data for 100% firing rate
Table K.
Typical Vent Pressure and Volume of Flue
Products
Vent
Volume of Flue
Products
CFM (cmm)
0.1
160 (5.53)
0.2
240 (6.80)
0.3
320 (9.06)
0.2
400 (11.33)
0.3
480 (13.59)
0.4
560 (15.86)
0,5
640 (18.12)
27
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