27
Rev. 0
COMBUSTION AND VENTILATION AIR
(DIRECT/NON-DIRECT VENT MODELS)
Direct Vent (Dual Pipe) Piping
Direct vent installations require both a combustion air in-
take and a vent/flue pipe. The pipes may be run horizon-
tally and exit through the side of the building or run verti-
cally and exit through the roof of the building. The pipes
may be run through an existing
unused chimney; however,
they must extend a minimum of 12 inches above the top of
the chimney. The space between the pipes and the chim-
ney must be closed with a weather tight, corrosion resis-
tant flashing. Both the combustion air intake and a vent/
flue pipe terminations must be in the same atmospheric
pressure zone. Refer to
Vent/Flue and Combustion Air Pipe
- Termination Locations or Concentric Vent Termination
section for specific details on termination construction. For
details concerning connection of pipes to the furnace, refer
to the
Vent/Flue Pipe and Combustion Pipe - Standard Fur-
nace Connections or Alternate Furnace Connections sec-
tion
.
Pipe
Size
(in.)
1
2
3
4
5
6
7
8
45,000
2
71
68
65
62
59
56
53
50
70,000
2
71
68
65
62
59
56
53
50
90,000
2
58
55
52
49
46
43
40
37
2
29
26
23
20
3
92
88
84
80
76
72
68
64
Direct Vent (Dual Pipe)
Maximum Allowable Length of Vent/Flue & Combustion
Air Intake Pipe (ft)
Number of Elbows
(1) (2) (3)
115,000
Not Recommended
Unit Input
(Btu)
(1)
Elbows and/or Tees used in the terminations must be included when
determining the number of elbows in the piping system.
(2)
Number of elbows tabulated are for each (Vent/Flue & Combustion air
intake) pipe.
(3)
Minimum length of each Vent/Flue & Combustion Air Intake pipe is
five feet and one elbow/tee.
Vent/Flue and Combustion Air Pipe Lengths and Di-
ameters
Refer to the following table for applicable length, elbows,
and pipe diameter for construction of the vent/flue and com-
bustion air intake pipe systems of a direct vent (dual pipe)
installation. The number of elbows tabulated represents the
number of elbows and/or tees in each (Vent/Flue & Com-
bustion Air Intake) pipe. Elbows and/or tees used in the
terminations must be included when determining the num-
ber of elbows in the piping systems.
If the combustion air intake pipe is to be installed above a
finished ceiling or other area where dripping of condensate
will be objectionable, insulation of the combustion air pipe
may be required. Use 1/2” thick closed cell foam insulation
such as Armaflex or Insultube where required.
Vent/Flue and Combustion Air Pipe Terminations
The vent/flue and combustion air pipes may terminate ver-
tically, as through a roof, or horizontally, as through an out-
side wall.
Vertical pipe terminations should be as shown in the fol-
lowing figure. Refer to
Vent/Flue Pipe and Combustion Pipe
- Termination Locations section for details concerning lo-
cation restrictions. The penetrations through the roof must
be sealed tight with proper flashing such as is used with a
plastic plumbing vent.
TEE
12" MIN.
12" MIN.
TO ROOF OR
HIGHEST
ANTICIPATED
SNOW LEVEL
VENT/FLUE
90º
MEDIUM RADIUS
ELBOWS
COMBUSTION
AIR INTAKE
24" MAX.
3" MIN.
SCREEN
Vertical Terminations (Dual Pipe)
Horizontal terminations should be as shown in the follow-
ing figure. Refer to
Vent/Flue Pipe and Combustion Pipe -
Termination Location section for location restrictions. A 2
3/8 inch diameter wall penetration is required for 2” diam-
eter pipe while a 3 1/2 inch diameter hole is required for 3”
diameter pipe. To secure the pipe passing through the wall
and prohibit damage to piping connections, a coupling
should be installed on either side of the wall and solvent
cemented to a pipe connecting the two couplings. The pipe
length 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 sili-
cone caulking material.
SCREEN
COMBUSTION
AIR INTAKE
VENT/FLUE
TEE
90º
MEDIUM RADIUS
ELBOW
12" MIN
12" MIN
12" MIN
3" MIN
24" MAX
3" MIN
24" MAX
Horizontal Terminations (Dual Pipe)
