Ultra Series Tankless Water Heater

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  • ENERGY STAR® Qualified
  • Energy Factor of .95 for Natural Gas and Propane
  • Built-in Rinnai Circ-LogicTM recirculation program cycles an external pump at pre-set intervals and temperatures to maximize efficiency and comfort (see brochure for more details)
  • Enhanced scale detection lessens possibility of serious, long-term damage to unit
  • Temperature lock function prevents accidental or unauthorized changes to water temperature
  • Complies with South Coast Air Quality Management District 14 ng/J or 20 ppm NOx emission levels
  • Multiple venting options available including PVC/CPVC using the Ubbink Concentric to Twin Pipe adaptor allow for an easy installation

RU98i (REU-KB3237FFUD-US) Gallery

What is a Rinnai Tankless Water Heater
What is a Rinnai Tankless Water Heater
Why Go Tankless Over a Tank Water Heater
Why Go Tankless Over a Tank Water Heater
Tankless Water Heaters are a Smart Investment
Tankless Water Heaters are a Smart Investment

Width: 18.3 Inches

Height: 26 Inches

Depth: 10 Inches


61.7 Pounds


Direct Electronic

Hot Water Capacity

0.26 to 9.8 GPM

Minimum Activation Rate

0.4 GPM

Minimum/Maximum Gas Rate (Input BTUs)

15,200 - 199,000

Energy Factor

0.95 for Natural Gas and Propane

Energy Star


Approved Gas Types

Natural Gas or Propane

Temperature Settings

98°F - 140°F with MC-91-2US

98° F - 185° F with MCC-91-2US

Type of Controller

MC-91-2US (included)

MCC-91-2US (optional for Commercial or Hydronic Applications)

MC-100V-1US Deluxe Controller (optional)

BC-100V-1US Bathroom Controller (optional)

Ultra Lox NOx



AC 120 Volts, 60 Hz

Electrical Consumption

Normal: 64 Watts

Standby: 2 Watts

Anti-Frost Protection: 146 Watts

Service Connections

Gas Supply: 3/4 Inch MNPT

Cold Water Inlet: 3/4 Inch MNPT

Hot Water Outlet: 3/4 Inch MNPT

* For complete information and details regarding Rinnai’s warranty, please visit
* To achieve temperatures over 140°F, an MCC-91 commercial controller must be purchased separately.
*** For complete information on gas sizing for Rinnai Tankless Water Heaters, consult the Operation and Installation Manual

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