Installation Guide

46 Rinnai Tankless Water Heater Installation and Operation Manual
3. Common Vent (Indoor Units Only. Direct Vent and Non-Direct/Room Air Vent)
Common venting allows multiple Rinnai
Tankless Water Heaters to share the same
vent system. When operating multiple water
heaters in a common venting system, it is
recommended to use Rinnai’s cascade cable
(purchased separately) which electronically
connects two water heaters so they function
as one hot water source.
Note: Multiple CXP models (water heaters with
a recirculation pump) cannot be electronically
connected using cascade cable. Cascade
cable connects only a CXP model with a CX
model. See illustration below.
Figure 39: Sample Inline, Freestanding
Configuration
Common Vent Maximum Equivalent Vent Lengths
Common vent equivalent lengths include
polypropylene pipe (PP) or PVC in a back-to
-back or inline configuration.
For the table below:
• Header is the main vent pipe into which
several vents connect.
• Vent Length is the distance from the end
of the header to the vent termination
• Maximum vent length starts at the end of
the header system.
Header
Vent length
Figure 40
Table 21. Common Vent Maximum Vent Length
Primary Secondary
Correct
CXP199i (With Pump) CX199i (Without Pump)
CX199i (Without Pump) CX199i (Without Pump)
CXP199i (With Pump) CXP199i (With Pump)
Not Correct
CX199i (Without Pump) CXP199i (With Pump)
Table 20. Primary and Secondary Water Heaters
Note: For common venting three or more units, refer to the “Common Vent Installation Instructions.”
Water Heater Model
# Water
Heaters
Max System Btu/hr
Vent Diameter
3 in. 4 in. 6 in.
CX199i, CXP199i 2 398,000
65 ft
(20 m)
150 ft
(46 m)
150 ft
(46 m)
CX160i, CXP160i 2 320,000
90 ft
(27 m)