Rinnai ThermaCirc360 RUR199i Installation And Operation Manual page 19

Select a Vent Type
Three types of venting options are available:
1
Direct Vent
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.
2
Non-Direct Vent
Room air is used for combustion while exhaust
vents to the outside.
Combustion
3
Common Vent
Multiple water heaters sharing a combustion air header
and a separate exhaust header that vents directly through
separate penetrations to the outside.
Rinnai Tankless Water Heater Installation and Operation Manual
(Concentric Pipe and Twin Pipe)
Concentric Pipe
Exhaust
Combustion
Combustion
air
(Room Air and External)
Room Air
Exhaust
air
(Indoor Units Only. Direct Vent and Non-Direct/Room Air Vent)
Direct Vent
Combustion Air
Combustion air and exhaust vent directly through
separate penetrations.
air
External (outdoor) water heater.
Multiple water heaters using room air for combustion
while sharing an exhaust header that vents directly to
the outside.
Exhaust
Twin Pipe
Combustion
air
Exhaust
External (Outdoor)
Exhaust
Combustion
air
Vent
Non-Direct (Room Air)
Exhaust
Room Air
For Combustion
19