Rinnai RU80i - Determining Total System Equivalent Length; Option 1: Vent Length Calculation Sheet; Option 2: Maximum Vent Length Tables

20 KB Series Manual
For PVC/CPVC vent systems reduce the maximum
allowable length for each elbow and terminaon type as
follows :


 For PVC/CPVC vent systems reduce the maximum
allowable length for each elbow and terminaon type
as follows:
 Vent and combuson air intake pipe diameters to be as
specied in maximum equivalent vent length tables of
this document.
 Do not exceed vent and combuson air intake pipe
MAXIMUM lengths (Lengths are specic to models and
fuel type).
 2.5 feet for every 45° elbow.
 5 feet for every 90° elbow.
 Terminaon (refer Approved Vent Component
table of this secon)

There are two opons for determining the vent lengths/
components necessary for the installaon.
The installer can use the vent length calculaon
sheet (below), lling in the quanty of the vent components
in order to calculate the total equivalent vent lengths.
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 specic terminaon
type and quanty of elbows.
Determining Total System Equivalent Length
(A blank copy of the Equivalent Vent Length Calculaon Sheet is located at the end of this secon)
Ensure switch #1 in the bank of eight tan dip switches is in OFF posion if vent length is greater than 21 (6.4m).

Choose the vent type and ll out the calculaon sheet
below. When determining equivalent combuson air and
vent length, add 5 feet for each 90° elbow, 2.5 feet for each
45° elbow.

 (assume 3” diameter pipes for
natural gas unit):
 Twin pipe (parallel) with snorkel terminal
 Combuson air pipe length: 40  straight pipe with 3 x
90° elbows
 Exhaust pipe length: 40  straight pipe with 3 x 90°
elbows 
 Snorkel Terminaon: 10 equivalent feet (reference
Approved PVC/CPVC Terminaon Components table)

 Equivalent Combuson air pipe length: [40+(3 X 5)+10]
= 65 
 Equivalent Vent Length: [40+(3 X 5)+10] = 65 
 Total = 65 . for both exhaust and combuson 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 conguraon
which is cered for up to 100 equivalent feet.
Maximum equivalent vent lengths are specic to the fuel
type of the water heater. It is imperave when performing
vent calculaons, the following be taken in consideraon:









1) 90 elbow
3

5

15
2) 45 elbow 
2.5

0
3) IPEX Low Prole Terminaon 
5

0
4) IPEX 4" Concentric Terminaon 
20

0
5) IPEX 3" Concentric Terminaon 
20

0
6)
3" Tee Terminaon

5

0
7)
4" Tee Terminaon

5

0
8) 3" Snorkel Terminaon
1

10

10
9) 4" Snorkel Terminaon 
10

0
10) Length of Straight Secon in feet NA
40

40
 (add up
lines 1 through
65