F
d
b
b l
&
h
B l M
l
Finned copper tube gas boilers & water heaters – Boiler Manual
12
F
F
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.
Th e 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). Th e chimney must provide a negative pressure
not greater than 0.15 inch, 3.8 mm w.c. at the boiler/water heater fl ue
collar with the unit running.
When using a listed metal chimney system the chimney
system manufacturer’s instructions must be followed.
Th e 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 fl ue, never connect any other appliances
to this fl ue. 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 fi red at less than 33% input.
CATEGORY II CHIMNEY
INSPECTION & SIZING
Masonry chimneys, when used, must be lined with a
metal liner certifi ed for Category IV venting.
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
unless properly lined to prevent draft problems.
Table 5 lists the minimum riser sizes required for the XLF boiler/
water heater.
Table 5
Riser diameters to common vent for Category II venting
Input — MBH
in
mm
2500/3000
12
305
3500/4000
14
356
Note: Th ese sizes are based on a 20 ft , 6.1m chimney height.
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
supported at 3 ft , 0.9 m intervals with overhead hangers.
Th e boiler vent connectors should be sloped up toward the breeching
at a minimum rate of ¼ in per ft, 21 mm per m. On masonry
chimneys the connector must terminate fl ush 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.
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!
