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Refer to the following tables for applicable length, elbows and pipe diameter for construction of the vent/flue pipe systems of a
nondirect vent (single pipe) installation. In addition to the vent/flue pipe, a single 90º elbow should be secured to the combustion air
intake to prevent inadvertent blockage. The tee used in the vent/flue termination must be included when determining the number of
elbows in the piping system.
Upflow
Nondirect Vent (Single Pipe) Maximum Allowable Length of Vent/Flue Pipe—ft (m)
Unit Input (Btu)
Pipe—in. (cm)
45,000
2 or 2¹⁄₂ (5.12 or 6.4)
70,000
2 or 2¹⁄₂ (5.12 or 6.4)
3 (7.6)
90,000
3 (7.6)
115,000
3 (7.6)
Counterflow
Direct Vent (Dual Pipe) Maximum Allowable Length of Vent/Flue Pipe—ft (m)
Unit Input (Btu)
Pipe—in. (cm)
70,000
2 or 2¹⁄₂ (5.12 or 6.4)
3 (7.6)
90,000
2 or 2¹⁄₂ (5.12 or 6.4)
3 (7.6)
NOTES:
One 90º elbow should be secured to the combustion air
intake connection.
Minimum requirement for each vent/flue pipe is 5 ft (1.5 m)
and 1 elbow/tee.
Tee used in the vent/flue termination must be included when
determining the number of elbows in the piping system.
The vent/flue pipe may terminate vertically, as through a roof,
or horizontally, as through an outside wall.
Vertical vent/flue pipe terminations should be as shown in
"Vertical Vent Termination (Single Pipe)" illustration. Refer to
"Termination Locations" in this section for details concerning
location restrictions.
The penetration of the vent through the roof must be sealed
tight with proper flashing such as is used with a plastic
plumbing vent.
Horizontal vent/flue pipe terminations should be as shown in
"Horizontal Vent Termination (Single Pipe)" illustration. Refer
to "Termination Locations" in this section for details
concerning location restrictions.
A 2³⁄₈" (6.1 cm) diameter wall penetration is required for 2"
(5.1 cm) diameter pipe.
A 3" (7.6 cm) diameter hole is required for a 2¹⁄₂" (6.4 cm)
pipe.
Nondirect Vent Applications
Number of Elbows
1
2
3
71 (21.6)
68 (20.7)
65 (19.8) 62 (18.9) 59 (18)
49 (14.9)
46 (14)
43 (13.1) 40 (12.2) 37 (11.3) 34 (10.4) 31 (9.5)
71 (21.6)
68 (20.7)
65 (19.8) 62 (18.9) 59 (18)
71 (21.6)
68 (20.7)
65 (19.8) 62 (18.9) 59 (18)
49 (14.9)
46 (14)
43 (13.1) 40 (12.2) 37 (11.3) 34 (10.4) 31 (9.5)
Number of Elbows
1
2
3
61 (18.6)
58 (17.7)
55 (16.8)
71 (21.6)
68 (20.7)
65 (19.8)
61 (18.6)
58 (17.7)
55 (16.8)
71 (21.6)
68 (20.7)
65 (19.8)
2¹⁄₂" or 3" (6.4 cm or 7.6 cm) diameter pipe can be used in
place of 2" (5.1 cm) diameter pipe.
Increased clearance configurations using two 45º long-sweep
elbows should be considered equivalent to one 90º elbow.
Vent/Flue Pipe Terminations
A 3¹⁄₂" (8.9 cm) diameter hole is required for 3" (7.6 cm)
diameter pipe.
To secure the pipe passing through the wall and prohibit
damage to the piping connections, a coupling should be
installed on either side of the wall and solvent cemented to a
length of pipe connecting the 2 couplings.
The length of pipe should be the wall thickness plus the
depth of the socket fittings to be installed on the inside and
outside of the wall.
The wall penetration should be sealed with silicone caulking
material.
In a basement installation, the vent/flue pipe can be run
between joist spaces.
NOTE: If the vent pipe must go below a joist and then up into
the last joist space to penetrate the header, two 45° elbows
should be used to reach the header rather than two 90°
elbows.
4
5
6
56 (17.1) 53 (16.2) 50 (15.2)
56 (17.1) 53 (16.2) 50 (15.2)
56 (17.1) 53 (16.2) 50 (15.2)
4
5
6
52 (15.8)
49 (14.9) 46 (14)
62 (18.9)
59 (18)
56 (17.1) 53 (16.2) 50 (15.2)
52 (15.8)
49 (14.9) 46 (14)
62 (18.9)
59 (18)
56 (17.1) 53 (16.2) 50 (15.2)
7
8
28 (8.5)
28 (8.5)
7
8
43 (13.1) 40 (12.2)
43 (13.1) 40 (12.2)
15
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