Tech Bulletin

TB-158
7/2019
DHW Setpoint
Temperature (°F)
140° 135° 130° 125° 120° 115° 110° 108° 106° 104° 102° 100° 98°
Typical Pump OFF
Intervals (Minutes)
9 10 11 12 14 16 19 20 22 24 26 28 31
Home includes dedicated hot water
and cold water lines.
PURPOSE: To announce the I-Series Condensing Combi Boiler oers DHW recirculaon and to explain
how DHW recirculaon works, the dierent recirculaon modes, and how to congure the boiler for
DHW recirculaon.
I-Series Condensing Combi Boiler Models: i060C, i090C, and i120C
DHW Recirculaon Facts:
• Recirculaon circulates hot water through the plumbing system, so hot water is always available in
whatever part of the house that the consumer may need it.
• Recirculaon requires an external recirculaon pump. For pump sizing, reference the “DHW
Pressure Drop and Flow Curve” in the Boiler Installaon and Operaon Manual.
• An oponal 24V mer can be used to set the me intervals and duraon of recirculaon (an
example mer is the Intermac® MIL72ASTUZ-24).
• Two recirculaon modes are available: Dedicated and Crossover:
Dedicated Mode:
• The plumbing system includes a dedicated hot water
return line.
• Recirculaon technology in the boiler decides if the
pump will turn on based on me intervals and DHW
setpoint temperature.
• How the recirculaon pump works:
− The pump turns ON and runs unl the DHW
return water temperature is within 6°F of the
setpoint temperature, or for 20 minutes,
whichever occurs rst.
− The pump stays OFF based on the DHW setpoint
temperature (as outlined in the table below).
Note: Rinnai strongly recommends installing insulaon to the hot water and dedicated return lines
to decrease the amount of heat loss.
Hot water
Cold water
Technical Bullen 158 - I-Series Boiler with DHW Recirculaon