Ths is from the Metal Fab web site
www.mtlfab.com
INSTALLATION:
Round B-Vent
The Type M B-Vent sections and components 3"-14" diameter use the
Metal-Fab positive twist lock for interconnections. Align the ends of the
vent, push together then twist section to lock in place. Use SureLock™
tab on 3"-6". See Detail 1. No additional fasteners are required to
assure a safe installation. It is acceptable to apply screws at the joints if
local code requires, or at the installing contractor’s option, provided that
the screws do not penetrate the flue.
1. Starting at the appliance outlet, attach the first section. It is acceptable
to use screws to attach the B-Vent to the appliance outlet. If
the appliance has a draft hood, the MDC draft hood connector is
attached to the top of the draft hood and the first B-Vent section is
twist-locked to the MDC.
2. If this is a single, straight up installation, and the B-Vent must penetrate
the ceiling, cut a hole in the ceiling 2 inches (51 mm) larger
than the outside diameter (OD) of the outer casing. The B-Vent is to
be centered in this opening. When installed, check to make sure the
one inch (25.4 mm) clearance to combustible has been maintained.
(See Figure 1).
3. When a combustible floor is penetrated by B-Vent, a MFS firestop
or MSP support plate is used to close the opening. If the area above
the ceiling is an attic, the firestop or support plate is mounted above
the joist to assure that insulation does not drop into the joist area.
4. Continue with B-Vent penetrating the roof. NOTE: For Canadian
installations, use labeled ULC section, designated with Suffix G, on
vent sections exposed to atmosphere. At the roof, the opening
should be 2 inches (51 mm) greater than the B-Vent OD. Above the
roof, a flashing is required to maintain the one inch (25.4 mm) clearance
to the combustibles of the roof. Installation of a storm collar
allows water to drain over the flashing. Caulk as shown in Figure 1.
5. Install the B-Vent cap (MC) onto the B-Vent. NOTE: See height of
vents under “SAFETY”.
6. If a UL Listed gas vent other than Metal-Fab is to be connected to
the inlet end of the Metal-Fab B-Vent, use the M6A, M12A, or
M18A gas vent adapter. Insert the male end of the other gas vent
into the gas vent adapter and secure by tightening the clamp on the
adapter (See Figure 2A). If Metal-Fab B-Vent is to be inserted
directly into the inlet end of a UL Listed gas vent other than MetalFab,
secure by using three (3) 1/4 inch (6.4 mm) long sheet metal
screws. Do not penetrate the flue (See Figure 2B).
7. Although it is not a preferred practice, there may be installations where
B-Vent must run vertically-exterior to the building – and wall support is
needed. A wall band (MH) or (MWB) is used by placing around the BVent,
then fastening to the wall. Using a wall band assures that the
clearance to combustibles is maintained (See Figure 3).
8. When the connector from the appliance is single wall, it must terminate
into B-Vent. At this termination, it is acceptable to secure the
joint with sheet metal screws. NOTE: Single wall connector, either
rigid or flexible, cannot be enclosed within combustible materials.
9. If the installation requires two appliances to terminate into a common
B-Vent, a B-Vent wye or tee is used. It is recommended that
the higher output appliance, normally the furnace, insert into the
bottom of the wye or tee and the other appliance attach to the tap.
To minimize the length of run and to provide maximum flexibility in
these installations, a swivel tee (MST) or swivel wye (MSY) is used.
These components provide 360 degrees of rotation to position the
tap in the proper orientation (See Figure 4). NOTE: Consult the
Metal-Fab catalog for the many variations of wyes and tees available.
10. It is a common practice to utilize the 90 degree adjustable elbow
(M90) in the appliance area to minimize vent run. Use of the M90 or
M45/60 elbow is acceptable and not limited to the appliance area.
11. For horizontal and lateral runs, it is recommended that support be
used every 5 feet (1524 mm). Plumbers straps are commonly used.
They should be positioned to maintain the 1 inch (25.4 mm) clearance
to combustibles.
12. If your installation requires a change in diameter due to vent capacity,
a B-Vent increaser (MI) is available. Installation is the same as
standard B-Vent Sections.
