LP-428 Rev. 6.6.16
26
Friction Loss Equivalent in Piping and Fittings
Fittings or Piping
Equivalent Feet
6” 8”
90 Degree Elbow* 3’ 3’
45 Degree Elbow 1’ 1’
Coupling 0’ 0’
Air Inlet Tee 0’ 0’
Straight Pipe 1’ 1’
V Series Vent Kit 1’ 1’
AL20 4c Vent Terminal 1’ 1’
b. For example: If the exhaust vent has two short 90
o
elbows
and 10 feet of PVC pipe we will calculate:
Exhaust Vent Equivalent Length = (2x3) + 10 = 16 feet.
Further, if the intake pipe has two 90
o
elbows, one 45
o
elbow, and 10 feet of PVC pipe, the following calculation
applies:
Intake Pipe Equivalent Length = (2x3) + 1 + 10 = 17 feet.
The total equivalent length is 43 feet, well below the
maximum of 200 feet.
c. Eort should be made to keep a minimum dierence in
equivalent length between the exhaust vent and intake
pipe.
2. The minimum total equivalent length is 16 feet.
Do not exceed the maximum lengths for vent pipes. Excessive
length could result in boiler shutdown and property damage.
F. Exhaust Vent and Intake Pipe Installation
All joints of positive pressure vent systems must be sealed
completely to prevent leakage of ue products into the living
space. Failure to do so could result in property damage,
serious injury, or death.
1. Use only solid PVC, CPVC, or stainless steel pipe or a
Polypropylene vent system approved for use with Category IV
appliances.
FOAM CORE PIPING IS NOT APPROVED FOR EXHAUST
VENT APPLICATIONS. Foam core piping may be used on air
inlet piping only.
2. Remove all burrs and debris from joints and ttings.
3. When using PVC or CPVC pipe, all joints must be properly
cleaned, primed, and cemented. Use only cement and primer
approved for use with the pipe material. Cement must
conform to ASTM D2564 for PVC and ASTM F493 for CPVC
pipe. NOTE: DO NOT CEMENT POLYPROPYLENE PIPE.
4. Ensure the vent is located where it will not be exposed to
prevailing winds.
5. In all roof venting applications, exhaust discharge must
point away from the pitch of the roof.
6. If the exhaust vent is to be terminated in a walled o area
(such as a roof with a parapet wall), ensure the exhaust vent
terminates a minimum of 10’ from nearest wall and extends
level with or above the top of the wall. This will ensure ue gas
does does not get trapped and possibly recirculated into the
intake air pipe, which could contaminate the combustion air.
7. To prevent water leakage, install adequate roof ashing
where the pipe enters the roof.
8. Do not locate vent over public walkways, driveways, or
parking lots. Condensate could drip and freeze, resulting in a
slip hazard or damage to vehicles and machinery.
9. Due to potential moisture build-up, sidewall venting may
not be the preferred venting option. To save time and cost,
carefully consider venting installation and location.
10. Horizontal lengths of exhaust vent must slope back towards
the boiler not less than ¼” per foot to allow condensate to
drain from the vent pipe.
11. The exhaust vent must terminate where vapors cannot
make accidental contact with people or pets, or damage
shrubs or plants.
12. In vacant chimney applications, install and seal a rain cap
over existing chimney openings.
13. All piping must be fully supported. Use pipe hangers at a
minimum of 4 foot intervals to prevent sagging of the pipe
where condensate may form.
14. Do not use the boiler to support any piping.
15. Ensure the outdoor exhaust vent termination is screened
to prevent blockage caused by debris or birds.
16. Ensure the outdoor intake pipe termination is screened to
prevent blockage caused by debris or birds.
Failure to provide a minimum total vent length of 16 equivalent
feet could result in property damage and improper product
operation.
E. Exhaust Vent and Intake Pipe Sizing
1. The maximum total equivalent length of exhaust vent and
intake pipe should not exceed the lengths in Table 8.
a. The equivalent length of elbows, tees, and other ttings
are listed in the Friction Loss Table.
Figure 10 - Transitioning to Larger Diameter Pipe
Model
Intake Pipe Exhaust Vent Max. Total Equivalent
Vent Length (Intake
and Exhaust)
Input De-Rate
Per 25’ of Vent
Intake Diameter Intake Min. Length Vent Diameter Vent Min. Length
MODCON1000 6”
16’
6”
16’ 150’ 2%
MODCON1700 8” 8”
Table 8 - Exhaust Vent and Intake Pipe Sizing
Table 9 - *Friction loss for long radius elbow is 1 foot less. NOTE:
Consult Polypropylene venting instructions for friction loss and
pressure drop equivalents.
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