Rinnai CX199I REU-NB3237FFC-US

Rinnai CX199I REU-NB3237FFC-US is a gas tankless water heater from Rinnai rated 5.8 GPM at a 0.98 UEF.

Efficiency
Uniform Energy Factor (UEF)	0.98
Annual gas use (natural gas)	173 therms/yr
Recovery efficiency	99 %
Annual propane use	189.07 gal/yr

General
Fuel	Natural Gas, Propane

Capacity
Max flow rate	5.8 GPM
Draw pattern	High
Minimum activation flow	0.1 GPM

Performance
Gas input rate	199 kBTU/h

Installation
Max current draw	4 A
Vent type	Power Direct Vent
Vent size	2

Smart features
Smart / connected capable	No

Dimensions
Height	25.8 in
Diameter	11.4 in
Width	18.5 in
Depth	11.4 in

Certification
ENERGY STAR certified	Yes

Real flow rate by climate

A tankless heater's usable flow depends on how far it must raise incoming water temperature. Sustained hot-water flow of the Rinnai CX199I REU-NB3237FFC-US at common temperature rises (a typical shower uses about 2 GPM of mixed water):

Temperature rise	Climate	Sustained flow	Simultaneous showers
45 °F	Warm climate (~75 °F groundwater)	5.8 GPM	2
55 °F	Mild climate (~65 °F groundwater)	5.8 GPM	2
70 °F	Cold climate (~50 °F groundwater)	5.6 GPM	2
77 °F	DOE test condition	5.1 GPM	2

Compare the Rinnai CX199I REU-NB3237FFC-US

Similar water heaters

A. O. Smith ACTH-199M-(N,P) 1 (UEF 0.95)
A. O. Smith T-H3-OS-N 1 (ACT-199O-N 1) (UEF 0.95)
A. O. Smith T-H3-OS-N 1 (ACT-199O-P 1-1) (UEF 0.95)
A. O. Smith T-H3-OS-N 1 (ATO-540H 1) (UEF 0.95)
A. O. Smith T-H3-OS-N 1 (ATO-540H 1-1) (UEF 0.95)
A. O. Smith T-H3-OS-N 1 (ATO-540HX3-N 1) (UEF 0.95)

Frequently asked questions

Is the Rinnai CX199I REU-NB3237FFC-US ENERGY STAR certified?

Yes, the Rinnai CX199I REU-NB3237FFC-US holds a current ENERGY STAR certification for water heating efficiency (UEF 0.98).

How much does the Rinnai CX199I REU-NB3237FFC-US cost to run per year?

About $251 per year at national average energy rates, based on its certified annual energy use under the DOE test draw pattern. Your rate and usage change this figure.

What venting does the Rinnai CX199I REU-NB3237FFC-US use?

The Rinnai CX199I REU-NB3237FFC-US uses Power Direct Vent venting with 2 in vent connections. Matching the existing vent type is usually the cheapest replacement path.

Is the Rinnai CX199I REU-NB3237FFC-US a smart water heater?

No, the Rinnai CX199I REU-NB3237FFC-US is not connected-capable — it has no app connectivity or demand-response support.

Sources

data.energystar.gov (retrieved 2026-07-17)