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SECTION VII: COMBUSTION AIR AND
VENT SYSTEM
COMBUSTION AIR AND VENT SAFETY
This Category IV, dual certified direct vent furnace is designed for resi-
dential or MH application. It may be installed without modification to the
condensate system in a basement, garage, equipment room, alcove,
attic or any other indoor location where all required clearance to com-
bustibles and other restrictions are met. The combustion air and the
venting system must be installed in accordance with Section 5.3, Air for
Combustion and Ventilation, of the National Fuel Gas Code Z223.1/
NFPA 54 (latest edition), or Sections 7.2, 7.3 or 7.4 of CSA B149.1,
National Gas and Propane Codes (latest edition) or applicable provi-
sions of the local building code and these instructions.
The "VENT SYSTEM" must be installed as specified in these
instructions for Manufactured (Mobile) Home and Modular Homes.
The sealed combustion air / vent system is the only configuration
that can be installed in a Manufactured (Mobile) Home.
Vertical vent termination must be secured for transit.
This furnace may not be common vented with any other appliance,
since it requires separate, properly sized air intake and vent lines.
The furnace shall not be connected to any type of B, BW or L vent
or vent connector, and not connected to any portion of a factory-
built or masonry chimney
The furnace shall not be connected to a chimney flue serving a sep-
arate appliance designed to burn solid fuel.
When combustion air pipe is installed above a suspended ceiling or
when it passes through a warm and humid space, the pipe must be
insulated with 1/2" Armaflex or other heat resistant type insulation if
two feet or more of pipe is exposed.
Vent piping must be insulated if it will be subjected to freezing tem-
peratures such as routing through unheated areas or through an
unused chimney.
COMBUSTION AIR/VENT PIPE SIZING
The size of pipe required will be determined by the furnace model, the
total length of pipe required and the number of elbows required.
Table 7 lists the maximum equivalent length of pipe allowed for each
model of furnace. The equivalent length of elbows is shown in Table 9.
The equivalent length of the vent system is the total length of straight
pipe PLUS the equivalent length of all of the elbows.
The following rules must also be followed:
1.
Long radius (sweep) elbows are recommended. Standard elbows
may be used, but since they have a longer equivalent length, they
will reduce the total length of pipe that will be allowed. Short radius
(plumbing vent) elbows are not allowed. The standard dimensions
of the acceptable elbows are shown below.
2.
The maximum equivalent length listed in Table 7 is for the vent pip-
ing and the air intake piping separately. For example, if the table
allows 65 equivalent feet for a particular model, then the vent can
have 65 equivalent feet of pipe, AND the combustion air intake can
have another 65 equivalent feet of pipe.
Johnson Controls Unitary Products
3.
Three vent terminal elbows (two for the vent and one for the com-
bustion air intake) are already accounted for and need not be
included in the equivalent length calculation.
4.
All combustion air and vent pipe must conform to American
National Standards Institute (ANSI) and American Society for Test-
ing and Materials (ASTM) standards D1785 (Schedule 40 PVC),
D2665 (PVC-DWV), F891 (PVC-DWV Cellular Core), D2261
(ABS-DWV) or F628 (Schedule 40 ABS). Pipe cement and primer
must conform to ASTM Standard D2546 (PVC) or D2235 (ABS). If
ABS pipe is to be used, any joint where ABS pipe is joined to PVC
pipe must be glued with cement that is approved for use with
BOTH materials. Metallic materials must not be used for venting or
air intake.
5.
If a flexible connector is used in the vent system, it must be made
of a material that is resistant to acidic exposure and to at least
225° F temperature. Flexible connectors are also allowed in the
combustion air pipe.
6.
All models are supplied with 2" vent connections. When the pipe
must be increased to 3" diameter, the transition from 2" to 3" must
be done as close to the furnace as possible. For upflow models,
the transition from 2" to 3" should be done immediately above the
furnace. For downflow or horizontal models, the transition from 2"
to 3" pipe should be done immediately after exiting the furnace.
7.
In Canada, vents shall be certified to ULC S636, Standard for Type
BH Gas Venting Systems.
8.
In Canada, the first three feet (900 mm) of the vent must be readily
accessible for inspection.
9.
For single pipe systems it is recommended to install the combus-
tion air coupling provided and install approximately 18" of PVC
pipe on the furnace.
10. Minimum vent length for all models is 5 feet.
TABLE 7: Maximum Equivalent Pipe Length
Model Input
Pipe Size
BTUH (kW)
Inches (cm)
60,000 (17.6)
60,000 (17.6)
80,000 (23.4)
80,000 (23.4)
100,000 (29.3)
100,000 (29.3)
120,000 (35.1)
A
STANDARD ELBOW
FIGURE 24: Dimensions
TABLE 8: Elbow Dimensions
Elbow
"A" Dimension
2" Standard
2-5/16"
3" Standard
3-1/16"
2" Sweep
3-1/4"
3" Sweep
4-1/16"
Dimensions are those required in Standard ASTM D-3311.
420705-UIM-C-0310
Maximum
Equivalent
length feet (m)
2 (5.1)
65 (19.8)
3 (7.6)
90 (27.4)
2 (5.1)
65 (19.8)
3 (7.6)
90 (27.4)
2 (5.1)
30 (9.2)
3 (7.6)
90 (27.4)
3 (7.6)
90 (27.4)
A
LONG (SWEEP) ELBOW
17
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