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Rinnai Tankless Water Heater Installation and Operation Manual
4.5.4 Venting Options
Three types of venting options are available:
1. Direct Vent
(Concentric Pipe and Twin Pipe)
2. Non-Direct Vent
(Room Air and External)
3. Common Vent
(Indoor Unit Only. Direct Vent and Non/Direct/Room Air Vent)
Concentric Pipe
Combustion air and exhaust
vent directly through a single
concentric connection. Hot
exhaust exits through the interior
tube, while combustion air enters
through the outer layer.
Twin Pipe
Combustion air and
exhaust vent directly
through separate
penetrations.
Room Air
Room air is used for combustion
while exhaust vents to the
outside.
External (Outdoor)
External (outdoor) water
heater.
Direct Vent
Multiple water heaters sharing a combustion
air header and a separate exhaust header that
vents directly through separate penetrations to
the outside.
Non-Direct (Room Air) Vent
Multiple water heaters using room air for
combustion while sharing an exhaust header
that vents directly to the outside.
Figure 15: Concentric Pipe
Figure 16: Twin Pipe
Figure 17: Room Air
Figure 18: External
Figure 20: Common Vent, Room Air
Figure 19: Common Vent, Direct Vent
