Combustion Air And Vent Piping Lengths - Rinnai Q85SN Installation & Service Instructions Manual

6.7.6 Combustion air and vent piping lengths.
Parallel system
Length tube
Combustion air
ft
Vent
ft
Concentric system
Length concentric
tube, boiler to roof
horizontal
ft
In the table below you find the maximum equivalent pipe length of the vent/air system
based on 3" diameter. These lengths are for single pipe (room air), twin pipe, and
concentric venting systems.
Boiler type
Q85
Q130
Q175
Q205
Equivalent vent length
Calculation of equivalent length vent system
Choose the vent type and fill out the corresponding table.
* When determining equivalent combustion air and vent length, add 6 feet for each
90° elbow, 3 feet for each 45° elbow, 5 feet for the concentric terminal in the Parallel
System, and 2 feet for the concentric terminal in the Concentric System .
Number of Number of
elbows 90° elbows 45°
x 6* x 3*
ft
ft
Number of Number of
elbows 90° elbows 45°
x 6* x 3*
ft
Example of calculation:
Twin tube (parallel) with terminal
Combustion air length
Vent length
Calculation:
Equivalent Air Length
Equivalent Vent Length
3" Max Vent equivalent length
100 feet
100 feet
80 feet
40 feet
Concentric Total
terminal
Add 5 ft.*
ft ft
ft ft
Total equivalent length
Concentric Total
terminal
Add 2 ft.*
ft ft
: 24 ft with elbow 3 x 90°
: 24 ft with elbow 2 x 90°, elbow 2 x 45°
: (24+3x6+2) x 0.5
: (24+2x6+2x3+2) x 0.5
Total
3" Max Air equivalent length
100 feet
100 feet
80 feet
40 feet
table 9
Multiply with Equivalent
factor
length
ft 0.5
ft 0.5
Multiply with Total equivalent
factor
length
ft 1.0
= 23 ft
= 23 ft +
= 46 ft.
ft
ft
ft
ft
31