An abandoned masonry chimney may be used as a raceway for properly insulated and supported combustion-air and vent pipes. Each furnace must
have its own set of combustion-air and vent pipes and be terminated individually, as shown in Fig. 46.
Other gas appliances with their own venting system may also use the abandoned chimney as a raceway providing it is permitted by local code,
the current edition of the NFGC or NSCNGPIC, and the vent or liner manufacturer’s Installation Instructions. Care must be taken to prevent the
exhaust gases from one appliance from contaminating the combustion air of other gas appliances.
Fig. 36—Combustion-Air and Vent Pipe Diameter Transition
Location and Elbow Configuration
A93034
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
Fig. 37—Combustion-Air and Vent Pipe Connections
A96187
COMBUSTION-
AIR
COMBUSTION-
AIR
AIR
FLOW
VENT
VENT
VENT
AIR
FLOW
AIR
FLOW
AIR
FLOW
UPFLOW
DOWNFLOW
HORIZONTAL-LEFT DISCHARGE
HORIZONTAL-RIGHT DISCHARGE
Select 1 vent pipe connection and
1 combustion-air pipe connection.
COMBUSTION-
AIR
COMBUSTION-
AIR
COMBUSTION-
AIR
COMBUSTION-
AIR
VENT
VENT
VENT
NOTE:
Select 1 vent pipe connection and
1 combustion-air pipe connection.
NOTE:
Table 8—Approved Combustion-Air and Vent Pipe, Fitting and Cement Materials
ASTM SPECIFICATION
(MARKED ON MATERIAL)
MATERIAL PIPE FITTINGS SOLVENT CEMENT AND PRIMERS
DESCRIPTION
D1527
ABS
Pipe
—
—
Schedule-40
D1785
PVC
Pipe
—
—
Schedule-40
D2235
For ABS
—
—
Solvent
Cement
For ABS
D2241
PVC
Pipe
—
—
SDR-21 & SDR-26
D2466
PVC
—
Fittings
—
Schedule-40
D2468
ABS
—
Fittings
—
Schedule-40
D2564
For PVC
—
—
Solvent
Cement
For PVC
D2661
ABS
Pipe
Fittings
—
DWV at Schedule-40 IPS sizes
D2665
PVC
Pipe
Fittings
—
DWV
F438
CPVC
—
Fittings
—
Schedule-40
F441
CPVC
Pipe
—
—
Schedule-40
F442
CPVC
Pipe
—
—
SDR
F493
For CPVC
—
—
Solvent
Cement
For CPVC
F628
ABS
Pipe
—
—
Cellular Core DWV at Schedule-40 IPS sizes
F656
For PVC
—
—
Primer
For PVC
F891
PVC
Pipe
—
—
Cellular Core Schedule-40 & DWV
—35—
Summary of Contents for PG9MAA
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