Section: INSPECT/PREPARE
INSTALLATION SITE
10
Chimney Liners
The new designs of furnaces and boilers are more
efficient. One result of increased efficiency is lower flue
gas temperatures. As flue gases rise in the chimney,
they cool and condense when they reach the dew
point. The condensation mixes with sulphur in the
flue gases creating sulfuric acid. The acid attacks the
chimney mortar, brick and clay liners causing corrosion,
deterioration, leaks, or blockage of the chimney.
Eventually the blockage could prevent exhausting
the flue gases. Instead, the flue gases vent out the
barometric damper into the living space.
Therefore it is strongly recommended that an approved
insulated stainless steel chimney liner be installed. The
installing contractor is solely responsible for installation
of the proper vent system.
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For those installations not requiring a chimney, such
as through-the-wall vented appliances, follow the
instructions given by the appliance and power venter
(if used) manufacturers.
Minimum Clearence: 2 FT.
NOTE:
Correct chimney design is shown by dotted lines. Incorrect chimney design, as shown by the solid
lines, may result in down-drafts.
Figure 7 –
Chimney Design - Above the Roof
5. Any leakage between chimney tiles, around
clean-out doors, or around the vent pipe should
be sealed.
6. A barometric draft control is required, it shall be a
double-acting type, agency recognized for use with
gas vent systems.
7. The design and sizing of the appliance’s vent
system shall comply with the requirements of
NFPA 54 Chapters 12 and 13.
8. A chimney flue shall extend at least 3 feet above
the highest point at which the chimney comes
in contact with the roof, and not less than 2 feet
above the highest roof surface or structure within
10 feet horizontally of the chimney. Refer to
.
Some local codes and gas
utilities require the installation of
a thermal flue Safety switch on the double-acting
draft control, or draft hood.
The thermal safety switch senses flue gas spillage
caused by blocked flue exhaust, prolonged down-draft,
or insufficient draft. The safety is wired in series with
the burner control circuit and shuts the burner off, when
the spillage of hot flue gases is detected.
