Option 4: Vertical Chimney Venting Negative Pressure - Category; Common Venting) Figure 8; Category Ii Chimney Inspection & Sizing; Category Ii Vent Connections - RBI Futera XLF Series Manual

option 4: VerticAL cHimney VentinG
neGAtiVe pressUre — cAteGory ii
(MultIple BoIlers WIth coMMon ventInG)
FiGUre 8
Category II venting is required for multiple XLF boilers
connected to a common vent. Common vent systems
cannot be pressurized.
The Futera XLF is listed as a Category II appliance when vented
vertically into a listed metal chimney system. See Figure 8, page 13
(multiple boilers). The chimney must provide a negative pressure
not greater than 0.15 inch, 3.8 mm w.c. at the boiler/water heater flue
collar with the unit running.
When using a listed metal chimney system the chimney
system manufacturer' s instructions must be followed.
The vent piping must be large enough to safely vent the
combined output of all of the appliances connected to
the system.
If an appliance using any type of a mechanical draft
system operating under positive pressure is connected
to a chimney flue, never connect any other appliances
to this flue. Doing so can result in excessive levels of
carbon monoxide which can cause severe personal
injury or death!
To ensure proper boiler operation, boilers that use
room air must not be fired at less than 33 % input.
12
Finned copper tube gas boilers & water heaters – Boiler manual
cAteGory ii cHimney
inspection & sizinG
A thorough inspection of the masonry chimney must be
performed to ensure that the chimney is clean, properly constructed,
lined and sized. Exterior masonry chimneys should not be used un-
less properly lined to prevent draft problems.
Table 5 lists the minimum riser sizes required for the XLF boiler/
water heater.
table 5
Input — MBH

cAteGory ii Vent connections

Locate the boiler/water heater as close to the chimney as
possible. Use the shortest, straightest vent connector possible for the
installation. If horizontal runs exceed 5 ft, 1.5 m they must be sup-
ported at 3 ft, 0.9 m intervals with overhead hangers.
The boiler vent connectors should be sloped up toward the breech-
ing at a minimum rate of ¼ in per ft, 21 mm per m. On masonry
chimneys the connector must terminate flush with the inside of the
chimney liner (as shown in Figure 6, page 10).
Always provide a minimum clearance of 6 inches, 152 mm between
single wall vent pipe and any combustible materials.
Masonry chimneys, when used, must be lined with a
metal liner certified for Category IV venting.
Riser diameters to common vent for Category II venting
in
3000 12
4000 14
Note: These sizes are based on a 20 ft, 6.1m chimney height.
Failure to maintain minimum clearances between vent
connectors and any combustible material can result in a
fire causing extensive property damage, severe personal
injury or death!
FTXLF-IOM-HN-1-110308 Copyright 2008 Mestek, Inc.
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