Rinnai RUCS65i Manuel D'installation Et D'utilisation page 23

IMPORTANT CONSIDERATIONS FOR LOCATION (continued):
Exhaust and Combustion Air Intake Pipe Diameters and
Maximum Lengths:

For PVC/CPVC vent systems reduce the maximum
allowable length for each elbow and termination type as
follows:

2.5 feet for every 45° elbow.

5 feet for every 90° elbow.

Termination (refer to the Approved Vent
Component table of this section)

Vent and combustion air intake pipe diameters must not
exceed the maximum equivalent vent lengths
referenced within this manual.

Do not exceed vent and combustion air intake pipe
MAXIMUM lengths (Lengths are specific to models and
fuel type).
Determining Total System Equivalent Length
There are two options for determining the vent lengths/
components necessary for the installation.
Option 1: The installer can use the vent length calculation sheet
(below), filling in the quantity of the vent components in order
to calculate the total equivalent vent lengths.
Option 2: The installer can use the maximum vent lengths tables
on the next pages to determine the amount of straight pipe that
can be used with a specific termination type and quantity of
elbows.
OPTION 1:
Calculation of equivalent piping lengths for venting system:
Choose the vent type and fill out the calculation sheet
Fitting / Termination Type
1) 90 elbow
2) 45 elbow
3) IPEX Low Profile Termination
4) IPEX 4" Concentric Termination
5) IPEX 3" Concentric Termination
6) Royal 3" Concentric Termination
7) Royal Low Profile Termination
3" Tee Termination
8)
4" Tee Termination
9)
10) 3" Snorkel Termination
11) 4" Snorkel Termination
12) Length of Straight Section in feet
(A blank copy of the Equivalent Vent Length Calculation Sheet is located at the end of this section)
Ensure SW1 in DIPSW 1 is in OFF position if vent length is greater than 21ft (6.4m).
Equivalent Vent Length Calculation Sheet
Number of
fittings
3
1
NA
KCM Series Manual
below. When determining equivalent combustion air and vent
length, add 5 feet for each 90° elbow, 2.5 feet for each 45° elbow.
Example of calculation (assume 3" diameter pipes for
natural gas unit):

Twin pipe (parallel) with snorkel terminal

Combustion air pipe length: 16 ft straight pipe with 2 x 90°
elbows

Exhaust pipe length: 16 ft straight pipe with 2 x 90°
elbows (include all interior and exterior elbows)

Snorkel Termination: 15 equivalent feet (reference
Approved PVC/CPVC Termination Components table)
Calculation:

Equivalent Combustion air pipe length: *16+(2 X 5)+ 15+ = 41 ft

Equivalent Vent Length: *16+(2 X 5)+15+ = 41 ft

Total = 41 ft. for both exhaust and combustion air pipes, which
is the maximum allowable vent length for 3" PVC/CPVC on a
natural gas unit. If longer lengths are required, go to the 4"
diameter pipe configuration which is certified for up to 100
ATTENTION
Maximum equivalent vent lengths are specific to the fuel type
of the water heater. It is imperative when performing vent
calculations the following be taken into consideration:
Vent Type
3" PVC/CPVC
Concentric PP
4" PVC/CPVC
Twin Pipe PP (Centrotherm)
Equivalent Vent
Length
5
x
x 2.5
x 5
x 20
20
x
20
5
5
x
5
x
x 15
x 15
40
Total (add up
lines 1 through
Maximum Equivalent Vent Length
41 Feet
41 Feet
100 Feet
41 Feet
Total Equivalent
Length
15
=
= 0
= 0
= 0
0
=
0
0
0
=
0
=
= 15
= 0
= 40
70
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