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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. Cement must conform
to ASTM Standard D2564 for PVC and Standard D2235
for ABS. PVC primer must meet standard ASTM F656.
When joining PVC piping to ABS, use PVC solvent cement.
(See procedure specified in 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.
Materials
SCHEDULE 40PVC ............................... D1785
PVC-DWV .............................................. D2665
SDR-21 & SDR-26 ................................. D2241
ABS-DWV .............................................. D2661
SCHEDULE 40 ABS .............................. F628
FOAM / CELLULAR CORE PVC ........... F891
FURNACE
FURNACE
MODELS
INSTALLATION
(BTU)
38,000
Upflow
Upflow
54,000
Downflow
Upflow
72,000
Downflow
Upflow
90,000
Downflow
108,000
Upflow
118,000
Downflow
Upflow
120,000
Downflow
1 Subtract 2.5 ft. for each additional 2 inch long radius elbow, 5 ft. for each additional 2 inch short radius elbow, 3.5 ft. for each additional 3
inch long radius elbow, and 7 ft. for each additional 3 inch short radius elbow. Subtract 5 ft for each 2" tee and 8 ft for each 3" tee.
2. Two 45 degree elbows are equivalent to one 90 degree elbow.
3. This table applies for elevations from sea level to 2,000 ft. For higher elevations, decrease pipe lengths by 8% per 1,000 ft of altitude.
4. A long radius elbow's centerline radius is equal to or greater than 1.5 times the vent diameter.
Vent Pipe Length & Diameter
In order for the furnace to operate properly, the combustion
air and vent piping must not be excessively restrictive.
• The venting system should be designed to have the
minimum number of elbows or turns.
• Transition to the final vent diameter should be done as
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
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
Standards
listed in
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.
SINGLE VENT PIPE LENGTH (FT.)
with 1 long radius elbow
OUTLET
OUTLET
2" Diameter
3" Diameter
50
70
70
50
50
60
60
N/A
N/A
N/A
N/A
†
NOTES:
Table 1. Vent Pipe Lengths
indicates the maximum allowable pipe length for
Table
1. Measure the linear length of your vent run
DUAL VENT PIPE LENGTH (FT.)
†
with 1 long radius elbow on each pipe
INLET / OUTLET
2" Diameter
70
50
90
70
90
70
90
50
90
50
90
60
90
60
90
N/A
90
N/A
90
N/A
90
N/A
†
INLET / OUTLET
3" Diameter
70
90
90
90
90
90
90
90
90
90
90
11
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