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The surfaces of the liner must be physically sound. If gaps or
holes are present, the metal liner must be removed and replaced
(Fix 4—Relining). Finally, confirm that the metal liner is the correct
size for the appliances to be installed. Use the GAMA tables and
rules.
NOTE: If a metal liner is not present, a clay tile liner must be
present, or the chimney must be lined (Fix 4—Relining).
Use a flashlight and small mirror at the cleanout or vent
connector to inspect the clay tile liner. If any of the following
problems are present, reline (Fix 4—Relining).
■
Tile sections misaligned
■
Tile sections missing
■
Gaps between tile sections
■
Signs of condensate drainage at the cleanout or vent
connectors
■
Mortar protruding from between tile sections
■
Use of sewer pipe or drainage pipe rather than an approved
fire clay tile
Next, measure the size of the liner. It may be possible to do this
from the cleanout. The liner must be at least as large as the
minimum size established by 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. If the liner is too small or too
large, then the chimney must be relined (Fix 4—Relining).
Check 6—Dilution Air
If gas-fired appliances are to be vented into a clay tile liner, a
source of dilution air is required.
Dilution air cannot be obtained through the following:
■
Induced draft appliances
■
Natural draft appliances with vent dampers
Sufficient dilution air can ordinarily be obtained through the draft
hood of a natural draft appliance only if the appliance’s vent
connector does not include a vent damper. If dilution air will not
be available, the chimney must be relined (Fix 4—Relining).
Check 7—Complete the Installation
If checks 1 through 6 have been satisfactory, and the liner is an
acceptable size as determined by 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, then the clay tile liner can
probably be used as a vent for the gas appliances. However, the
installer must keep in mind the following factors which may
render the tile liner unsuitable for use as a vent:
■
Extremely cold weather
■
Long vent connectors
■
Masonry chimneys with no air gap between the liner and the
bricks—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—Relining).
Fix 1—Liner Termination
Any cap or roof assembly used with a liner must be approved by
the liner manufacturer for such use. The liner and cap/roof
assembly 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—Relining.”
Fix 2—Change Venting Arrangements
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.
Fix 3—Rebuild the Crown
If the chimney crown is damaged, a qualified mason must repair
it in accordance with nationally recognized building codes or
standards. One such standard which may be referenced is the
Standard for Chimneys, Fireplaces, Vents, and Solid Fuel Burning
Appliances, ANSI/NFPA 211.
Fix 4—Relining
Relining options include B-vent and flexible liners.
If the chimney has diagonal offsets, B-vent probably cannot be
used.
If B-vent is to be used, it must be supported adequately.
Supports (such as fire stops or thimbles) must be used to keep
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
according to 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, such as:
■
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.
