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Category IV appliances operate with positive vent pressure
and therefore require vent systems which are thoroughly
sealed. They also produce liquid condensate, which is
slightly acidic and can cause severe corrosion of ordinary
venting materials. Furnace operation can be adversely
affected by restrictive vent and combustion air piping.
The inducer assembly on this furnace can be rotated to
vent the flue products out of the top, left or right side. This
increases the flexibility of which direction the vent pipe
can exit the furnace.
Vent Pipe Material
Vent and combustion air pipe and fittings must be one
of the following materials in the list and must conform to
the indicated ANSI/ASTM standards.
MATERIALS STANDARDS
Schedule 40PVC ......................................................D1785
PVC-DWV .................................................................D2665
SDR-21 & SDR-26 ....................................................D2241
ABS-DWV ................................................................. D2661
Schedule 40 ABS .....................................................F628
Foam / Cellular Core PVC ........................................F891
*PolyPro
®
by DuraVent ..............................................ULC-S636
*When using PolyPro
®
, all venting and fittings must be from the same
manufacturer with no interchanging of other materials. Refer to specific
instructions supplied with the PolyPro vent kits
When joining PVC to PVC, use cement that conforms to
ASTM standard D2564. PVC primer must meet standard
ASTM F656. When joining ABS to ABS, use cement that
conforms to ASTM standard D2235. When joining PVC
to ABS, use cement as specified in procedure from ASTM
standard D3138.
In Canada, all plastic vent pipes and fittings including
any cement, cleaners, or primers must be certified as a
system to ULC S636. However this requirement does not
apply to the finish flanges or piping internal to the furnace.
Vent Pipe Length & Diameter
In order for the furnace to operate properly, the combustion
air and vent piping must not be excessively restrictive.
• The ventingsystemshouldbedesignedtohavethe
minimum number of elbows or turns.
• Transitiontothenalventdiametershouldbedoneas
close to the furnace outlet as practical.
• Always use the same size or a larger pipe for
combustion air that is used for the exhaust vent.
Table 1 (page 10) indicates the maximum allowable pipe
length for a furnace of known input rate, when installed
with piping of selected diameter and number of elbows. To
use the table, the furnace input rate, the centerline length
and the number of elbows on each pipe must be known.
When estimating the length of vent runs, consideration
must be made to the effect of elbows and other fittings.
This is conveniently handled using the idea of “equivalent
length”. This means the fittings are assigned a linear
length that accounts for the pressure drop they will cause.
For example: a 2” diameter, long radius elbow is worth
the equivalent of 2.5 feet of linear run. A 90 degree tee
is worth 7 ft.
The equivalent lenghts of tees and various elbows are
listed in Table 1. Measure the linear length of your vent run
and then add in the equivalent length of each fitting. The
total length, including the equivalent fitting lengths, must
be less than the maximum length specified in the table.
Vent Pipe Installation
CAUTION:
This furnace has been certified for installation with zero
clearance between vent piping and combustible surfaces.
However, it is good practice to allow space for convenience
in installation and service.
• In the absence of local codes, the location of any
combustion air inlet relative to any vent terminal
must be at least 8 inches. This includes installations
involving more than one furnace.
• Thequalityofoutdoorairmustalsobeconsidered.Be
sure that the combustion air intake is not located near a
source of solvent fumes or other chemicals which can
cause corrosion of the furnace combustion system.
(See
page 5 for a sample list of substances).
• Routepipingasdirectaspossiblebetweenthefurnace
and the outdoors. Horizontal piping from inducer to
the flue pipe must be sloped 1/4” per foot to ensure
condensate flows towards the drain tee or PVC trap.
Longer vent runs require larger pipe diameters. Refer
to the Inducer & Venting Options section on page 17
for additional information.
• IfaDirectVent(2-pipe)systemisused,thecombustion
air intake and the vent exhaust must be located in the
same atmospheric pressure zone. This means both
pipes must exit the building through the same portion
of exterior wall or roof as shown in Figure 35 (page 46)
or Figure 40 (page 51).
• Piping must be mechanically supported so that its
weight does not bear on the furnace. Pipe supports
must be installed a minimum of every five feet along the
vent run to ensure no displacement after installation.
Supports may be at shorter intervals if necessary to
ensure that there are no sagging sections that can trap
condensate. It is recommended to install couplings
along the vent pipe, on either side of the exterior
wall (Figure 35 or Figure 40). These couplings may be
required by local code.
• If breakable connections are required in the
combustion air inlet pipe (if present) and exhaust vent
piping, then straight neoprene couplings for 2” or 3”
piping with hose clamps can be used. These couplings
can be ordered through your local furnace distributor.
To install a coupling:
1. Slide the rubber coupling over the end of the pipe that
is attached to the furnace and secure it with one of the
hose clamps.
2. Slide the other end of the rubber coupling onto the other
pipe from the vent.
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