PRODUCT DESIGN
24
If B vent is to be used, it must be supported adequately.
Supports (such as fire stops or thimbles) must be used to
prevent the B vent from coming into direct contact with the
tile liner or chimney walls. Direct contact would result in
higher heat loss, with an increased possibility of poor vent-
ing system performance.
It is not acceptable to vent one appliance inside the B vent
and other appliances outside. The excess space between
the B vent and the chimney walls must be covered at the
top of the chimney by a weatherproof, corrosion resistant
flashing.
The B vent should then be topped with a listed vent cap.
The listed vent cap will, when installed per the manufacturer’s
instructions, prevent problems due to rain, birds, or wind
effects.
A B vent installed as described in this section is consid-
ered to be an enclosed vent system, and the sizing tables
in National Fuel Gas Code NFPA 54/ANSI Z223.1 - latest
edition and in the National Standard of Canada, CAN/CGA
B149.1 and CAN/CGA B149.2 - latest editions and amend-
ments may be used.
If a flexible liner is to be used, it must be made of the proper
materials:
•
For most residential applications, an aluminum liner
should be acceptable.
•
If the combustion air supplied to the furnace will be
contaminated with compounds containing chlorine or
fluorine, a liner of AL29-4C stainless steel should be
used. Common sources of chlorine and fluorine com-
pounds include indoor swimming pools and chlorine
bleaches, paint strippers, adhesives, paints, var-
nishes, sealers, waxes (which are not yet dried) and
solvents used during construction and remodeling.
Various commercial and industrial processes may
also be sources of chlorine/fluorine compounds.
•
Heavier gauge 300 and 400 series stainless steel lin-
ers were developed for use with oil or solid fuel appli-
ances. They are not suitable for use with gas-fired
appliances. Flexible liners specifically intended and
tested for gas applications are listed in the UL "Gas
and Oil Equipment Directory". (UL Standard 1777).
For sizing of flexible liners, see Note 22 and the tables in
the National Fuel Gas Code NFPA 54/ANSI Z223.1 - latest
edition and in the National Standard of Canada, CAN/CGA
B149.1 and CAN/CGA B149.2 - latest editions and amend-
ments.
To install the liner, read and follow the liner manufacturer’s
instructions and your local codes. Excess liner length
should be pulled out of the chimney and cut off. Use cau-
tion when doing this, as the cut edges of flexible liners may
be sharp. Do not spiral excess liner inside of the chimney.
Support the liner as recommended by the liner manufac-
turer.
Some manufacturers of flexible liners offer an insulation sleeve
designed to be added to the liner before it is installed in the
chimney. (Poured insulation, either vermiculite or other ma-
terials, is no longer recommended.) Insulation will need to
be added to the flexible liner if:
•
It is required by the liner manufacturer’s instructions.
•
The previous liner was properly sized and installed,
and suffered from condensation damage.
•
It is required by your local building codes.
Even if none of those three conditions exist which require
additional liner insulation, the installer may wish to consider
it if:
•
The local climate is very cold.
•
The chimney is very tall.
•
The vent connectors used are very long or have a large
number of elbows.
•
Local experience indicates that flexible liners installed
without insulation are likely to have condensation prob-
lems.
Insulation must be selected and installed in accordance with
the liner manufacturer’s instructions.
Finally, cap the chimney and terminate the liner in accor-
dance with the liner manufacturer’s instructions.
Horizontal Applications and Considerations
Horizontal applications, in particular, may dictate many of
the installation’s specifics such as airflow direction, duct-
work connections, flue and/or combustion air pipe connec-
tions, etc. Never install a furnace on its back. Furnace and
coil must be adequately supported.