13
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 venting 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 considered 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/CSA B149.1 and CAN/CSA B149.2 - latest
editions and amendments 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 AL 29-4C stainless steel should be
used. Common sources of chlorine and fluorine
compounds include indoor swimming pools and chlorine
bleaches, paint strippers, adhesives, paints, varnishes,
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 liners
were developed for use with oil or solid fuel appliances.
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 the tables in the National Fuel Gas
Code NFPA 54/ANSI Z223.1 - latest edition and in the National
Standard of Canada, CAN/CSA B149.1 and CAN/CSA B149.2 - latest
editions and amendments.
To install the liner, read and follow the liner manufacturer’s in-
structions and your local codes. Excess liner length should be
pulled out of the chimney and cut off. Use caution 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 recom-
mended by the liner manufacturer.
Some manufacturers of flexible liners offer an insulation sleeve
designed to be added to the liner before it is installed in the chim-
ney. (Poured insulation, either vermiculite or other materials, is
no longer recommended.) Insulation will need to be added to the
flexible liner if:
•
It is required by the liner manufacturer’s instructions.
•
Extremely cold weather
•
Long vent connectors
•
Masonry chimneys with no air gap between the liner and
the bricks. (In practice, this can be difficult to detect.)
•
Exterior chimneys (The tables in National Fuel Gas Code
NFPA 54/ANSI Z223.1 - latest edition and in the National
Standard of Canada, CAN/CSA B149.1 and CAN/CSA B149.2
- latest editions and amendments assume interior
chimneys.)
If, in the judgment of the local gas utility, installer, and/or local
codes; one or more of the above factors is likely to present a
problem, the chimney must be relined (Fix 4).
F
IX
1 - L
INER
T
ERMINATION
Any cap or roof assembly used with a liner must be approved by
the liner manufacturer for such use. The liner and cap/roof as-
sembly must then terminate above the roof in accordance with the
manufacturer’s instructions.
In some cases, a shorter extension above the roof may be possible
with a liner than would be required with a masonry chimney.
For further information on relining, see Fix 4.
F
IX
2 -C
HANGE
V
ENTING
A
RRANGEMENTS
If the masonry chimney has more than one channel, it may be
possible to vent the gas appliances into one channel and vent the
solid or liquid fuel appliance(s) into another channel(s). Do not
vent an 80+ Furnace inside of a metal liner with other appliances
vented outside the liner.
Alternatively, the homeowner may agree to discontinue use of the
fireplace (solid fuel appliance). If so, the tile liner must be cleaned
to remove creosote buildup. The fireplace opening must then be
permanently sealed.
If oil-fired appliance(s) are being replaced by gas-fired
appliance(s), the tile liner must first be cleaned to remove the fuel
oil residue.
If none of the above options is practical, the furnace may need to
be vented vertically with a B Vent.
Under some conditions, a 90%+ furnace could be installed rather
than an 80% furnace. The 90%+ furnace can be vented horizontally
or vertically through PVC pipe.
F
IX
3 - R
EBUILD
THE
C
ROWN
If the chimney crown is damaged, a qualified mason must repair it
in accordance with nationally recognized building codes or stan-
dards. One such standard which may be referenced is the Stan-
dard for Chimneys, Fireplaces, Vents, and Solid Fuel Burning Ap-
pliances, ANSI/NFPA 211.
F
IX
4 - R
ELINING
Relining options include B vent and flexible liners.
If the chimney has diagonal offsets, B vent probably cannot be
used.
