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Venting System Length Calculations
The Total Equivalent Vent Length (TEVL) for
EACH
combustion air or vent pipe equals the length of the venting system, plus the equivalent
length of elbows used in the venting system from Table 17.
Standard vent terminations or factory accessory concentric vent terminations count for zero deduction.
See vent system manufacturer’s data for equivalent lengths of flexible vent pipe or other termination systems.
DO NOT ASSUME
that one
foot of flexible vent pipe equals one foot of straight PVC/ABS DWV vent pipe.
Compare the Total Equivalent Vent Length to the Maximum Equivalent Vent Lengths in Table 16.
Example 1
A direct-vent 60,000 BTUH furnace installed at 2100 ft. (640M). Venting system includes
FOR EACH PIPE:
70 feet (22 M) of vent pipe, 65 feet (20 M) of combustion air inlet pipe, (3) 90º long-radius elbows, (2) 45º long-radius elbows, and a factory
accessory concentric vent kit.
Can this application use 2” (50 mm ND) PVC/ABS DWV vent piping?
Measure the required linear length of air inlet and
vent pipe; insert the longest of the two here
70 ft.
(22 M)
Use length of the longer of the vent
or air inlet piping system
Add equiv length of (3) 90º long-radius elbows
(use the highest number of elbows for either the
vent or inlet pipe)
3
x
3 ft.
(0.9 M)
=
9 ft.
(2.7 M)
From Table 17
Add equiv length of (2) 45º long-radius elbows
(use the highest number of elbows for either the
vent or inlet pipe)
2
x
1.5 ft.
(0.5 M)
=
3 ft.
(0.9 M)
From Table 17
Add equiv length of factory concentric vent term
0 ft.
From Table 17
Add correction for flexible vent pipe, if any
0 ft.
From Vent Manufacturer’s
instructions; zero for PVC/ABS DWV
Total Equivalent Vent Length (TEVL)
82 ft.
(25 M)
Add all of the above lines
Maximum Equivalent Vent Length (MEVL)
95 ft.
(29 M)
For 2” pipe from Table 16
Is TEVL less than MEVL?
YES
Therefore, 2” pipe MAY be used
Example 2
A direct-vent 60,000 BTUH furnace installed at 2100 ft. (640M). Venting system includes
FOR EACH PIPE:
100 feet (30 M) of vent pipe, 95 feet (29 M) of combustion air inlet pipe, (3) 90º long-radius elbows, and a polypropylene concentric vent kit.
Also includes 20 feet (6.1 M) of flexible polypropylene vent pipe, included within the 100 feet (30 M) of vent pipe.
VERIFY FROM POLYPROPYLENE VENT MANUFACTURER’S INSTRUCTIONS for the multiplier correction for flexible vent pipe.
Can this application use 60mm o.d. (2”) polypropylene vent piping? If not, what size piping can be used?
Measure the required linear length of
RIGID
air inlet and vent pipe; insert
the longest of the two here: 100 ft. Of rigid pipe --- 20 ft. Of flexible pipe
=
80 ft.
(24 M)
Use length of the longer of the vent
or air inlet piping system
Add equiv length of (3) 90º long-radius elbows
(use the highest number of elbows for either the
vent or inlet pipe)
3
x
5 ft.
(1.5 M)
=
15 ft.
(4.6 M)
Example from polypropylene vent
manufacturer’s instructions, Verify from vent
manufacturer’s instructions.
Add equiv length of 45º long-radius elbows
(use the highest number of elbows for either the
vent or inlet pipe)
0
x
=
0 ft.
(0 M)
Add equiv length of factory concentric vent term
9
x
3.3 ft
(0.9 M)
=
30 ft.
(9 M)
Add correction for flexible vent pipe, if any
2*
x
20 ft.
(6.1 M)
=
40 ft.
(12.2 M)
*
VERIFY FROM VENT MANUFACTURER’S INSTRUCTIONS; For example only, assume 1 meter of flexible 60mm (2”) or 80mm (3”)
polypropylene pipe equals 2.0 meters (6.5 ft.) of PVC/ABS pipe.
Total Equivalent Vent Length (TEVL)
165 ft.
(50 M)
Add all of the above lines
Maximum Equivalent Vent Length (MEVL)
95 ft.
(29 M)
For 2” pipe from Table 16
Is TEVL less than MEVL?
NO
Therefore, 60mm (2”) pipe may NOT be
used; try 80mm (3”)
Maximum Equivalent Vent Length (MEVL)
185 ft.
(57 M)
For 3” pipe from Table 16
Is TEVL less than MEVL?
YES
Therefore, 80mm (3”) pipe MAY be used
922SA
