DuraVent DuraFlex AL Installation - Manual (Page 6)

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Figure 4
Figure 3
OPTIONAL
HIGH
WIND
CAP
OPTIONAL
HIGH
WIND
CAP
is intended for warm interior masonry
chimneys, enclosed within the building
on all four sides, and thus exposed to
cold outdoor temperatures only above
the roof line.
In cold climates, it is preferable to
switch to double-wall, air insulated
Type B Gas Vent near the top
exposed portion of the chimney (Figure
2). At the top of the chimney, the flue
gas has lost much of its heat, and
is therefore susceptible to corrosive
condensation and poor draft. This is
particularly true with fan-assisted gas
appliances.
In the event that the existing masonry
chimney is relatively short in height,
the draft may be too weak for proper
performance of the appliance and
venting system. By switching to
Type B Gas Vent at the top of the
chimney, the installer has the option
of extending the height of the venting
system (Figure 3).
For exterior masonry chimneys,
typically exposed on one or more
sides to cold outdoor temperatures,
a 100% Type B Gas Vent Chimney
Liner system is preferable (Figure 4).
In the event that the exterior masonry
chimney is constructed with an offset,
single-wall flex will be necessary
below the offset, with Type B Gas Vent
above the offset.
If you decide to install the Flexible
Liner, the DuraFlex AL kit is available
for convenience. The kit includes: a
DuraFlex AL Cap, Top Plate, Mortar
Sleeve, and a 15’, 25’, or 35’ length of
DuraFlex liner. Any additional parts
will need to be ordered separately.