Rinnai RU199i Installation And Operation Manual page 28

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