PRODUCT DESIGN
27
If dilution air will not be available, the chimney must be re-
lined (Fix 4).
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 Na-
tional 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 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 unsuit-
able for use as a vent:
•
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/CGA B149.1
and CAN/CGA B149.2 - latest editions and amend-
ments 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).
Fix 1 - Liner Termination.
Any cap or roof assembly used with a liner must be ap-
proved 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.
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 are practical, the 80% furnace
may need to be vented vertically with B vent.
Under some conditions a 90%+ furnace could be installed
rather than an 80%. The 90% furnace can be vented hori-
zontally 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 refer-
enced 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
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 flash-
ing.
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 edi-
tion 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.
