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14 | Installation instructions
pipe (metal double wall Type B), or an approved clay flue liner
or a listed chimney lining system must be used when venting
into a naturally drafting, internal masonry chimney. Local
codes may require the use of both gas vent and an approved
lining system when venting into a masonry chimney. The
Commonwealth of Massachusetts requires the use of a listed
liner. Lining systems include approved clay flue lining, a listed
chimney lining system or other approved material that will
resist corrosion, erosion, softening, or cracking from exhaust
flue gases at temperatures up to 1800 degrees F. The lining
system must be listed for use with naturally drafting, draft hood
equipped gas appliances. Follow local codes and refer to NFGC
54 and NFPA 58.
Existing interior masonry chimney
The metal gas vent pipe should be permanently mounted inside
the masonry chimney. Double wall Type B gas vent is
recommended. The masonry chimney may have to be tile or
metal lined before the insertion of the gas vent pipe; check local
codes for clarification. The lining material must be listed for use
only with naturally drafting, draft hood equipped gas
appliances. Follow manufactures instructions for installation of
listed lining material. You may not vent any other fuel burning
appliances into any free space remaining in the chimney. The
minimum vertical gas vent length within the masonry chimney
should be no less than 6 ft (1.8 m); the vent terminator should
extend at least 3 feet (0.9 m) above where the chimney meets
the roofline and at least 2 feet (0.6 m) higher than any vertical
wall or similar obstruction within 10 feet (3.1 m). The top of the
gas vent should have an approved vent terminator. See Fig.
11.
6 720 644 951 (2014/11)
ESTABLISH A ONE
FOOT RISE
BEFORE
ANY ELBOWS
Fig. 10
Pitch roof
[1] Listed vent cap
[2] Lowest discharge opening
[3] Listed gas vent
[H] H (minimum) height from roof to lowest discharge
opening
[X] Roof pitch is X/12
[A] Minimum 6 feet (1,8m)
GAS VENT TERMINATIONS FOR LISTED VENT CAPS
Roof pitch
Flat to 6/12
6/12 to 7/12
Over 7/12 to 8/12
Over 8/12 to 9/12
Over 9/12 to 10/12
Over 10/12 to 11/12
Over 11/12 to 12/12
Over 12/12 to 14/12
Over 14/12 to 16/12
Over 16/12 to 18/12
Over 18/12 to 20/12
Over 20/12 to 21/12
Table 5
H (minimum) feet
meters
1.0
0.30
1.25
0.38
1.5
0.46
2.0
0.61
2.5
0.76
3.25
0.99
4.0
1.22
5.0
1.52
6.0
1.83
7.0
2.13
7.5
2.27
8.0
2.44
330 PN
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