Frequently Asked Questions

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Buyer's Information

Rinnai tankless water heaters are perfectly suited for virtually any commercial application. They are very versatile. Customers of all sizes and configurations in multi-family, hospitality, healthcare, education, food service, retail and much more trust Rinnai to deliver an unlimited, efficient supply of hot water.

The flexibility and capability of our Rinnai tankless rack system (TRS) allows it to replace just about any existing water heating product, from domestic boilers to traditional tank-style water heaters, as long as the necessary gas, venting and installation requirements are present. In fact, our modular design can handle up to 4.9M BTU. Even in cases where the hot water demands are smaller, Rinnai tankless water heaters can provide significantly more energy efficiency and reliability than tank-style water heaters.

The CU199 models are dedicated commercial condensing models.

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Yes, there are some differences for the CU199 which include:

Built in cascade controller to link up to 24 units
A Thermal Efficiency rating (96 97% thermal efficiency)
New common venting configurations (room air and sidewall intake with vertical exhaust)
Temperature settings from 98°F to 185°F, right out of the box

The CU199 has a 97% thermal efficiency and a Uniform Energy Factor (UEF) of 0.93

Uniform Energy Factor (UEF) calculates a water heater's overall energy efficiency with other heaters with similar hot water output over a 24-hour period. On the contrary, Thermal Efficiency is the amount of energy delivered as heated water compared to the energy consumption of the water heater. The two figures are related but different and the Thermal Efficiency calculation is used specifically for commercial applications.

Yes, the tankless rack system comes standard with the CU199 for most applications, however there are other options that utilize the Rinnai RU and RUR units if you desire a recirculation pump internal to the tankless unit. These units are configured with Temperature settings from 98°F to 185°F, right out of the box.

The commercial warranty is 8 years on the HEX or 12,000 hours of operation, five (5) years on parts, and one (1) year on labor.

No. The CU199 models are for commercial use only.

No. The CU199 is for commercial use only and is not certified for use in mobile homes.

The Demand Duo® R-Series is a certified single appliance by CSA. The Demand Duo® H-Series is an assembly with multiple and separately certified components- tank, CU199 tankless, controller, and pump are standalone certified components.

Good news! Yes, the Rinnai Demand Duo® is designed to work in a multi-unit tank system regardless of manufacturer.

The Demand Duo® H-Series line-up utilizes condensing technology that includes the CU199 tankless with 97% Thermal Efficiency. The Demand Duo® R-Series utilizes non-condensing technology that includes the RLR94 tankless with 80% Thermal Efficiency.

The CU199 should qualify for tankless rebates. However, due to differences in state and regional spec, rebates must be verified locally.

The Demand Duo® H-Series model CHS13080H is suitable for residential or light commercial use.

For more information on Rinnai’s robust line of residential products, visit

Yes, you can combine a traditional tank with a tankless water heater. The Demand Duo® is a hybrid solution combining the best features of both the tankless water heater and a storage tank. With the Demand Duo® 2 or 2V you can get up to 398,00 Btu delivering up to 551 gallons in the first hour. Depending upon your specific application you may require more tankless units connecting to a storage tank so we invite you to consult with Rinnai’s Applications Engineering Team at 800-621-9419 or to determine the best solution for your project. We are here to help.

Yes, in fact Rinnai has been offering their National Accounts Program since 2016. We have Commercial Service Providers available across the US to provide emergency as well as planned replacement installation, service and maintenance. Please contact us at 844-348-4714 to inquire about becoming a Rinnai National Account today.


Thermal Efficiency is the amount of energy delivered as heated water compared to the energy consumption of the water heater.

CU199 models come with an MC-91-2 temperature controller (integrated into indoor models; provided with outdoor models) with temperature ranges from 98°F to 185°F. They do not require the MCC-91 temperature controller.

There are multiple, flexible venting options available with either twin pipe 2" or 3" Schedule 40 PVC/CPVC or 2"x4" 0r 3"x5" Concentric venting. You can also common vent up to 12 units using Rinnai supplied Polypropylene or Schedule 40 PVC/CPVC.

Room air common vent with vertical exhaust
Common venting with sidewall intake with vertical exhaust
Common venting is ULC S636-approved

Yes, they may be installed together and common vented or tied into a recirculation loop. Both the Demand Duo® H-Series and R-Series have the capability to control building recirculation with the New DuoSmart Digital Controller.

It varies based on the geographical location and application conditions. However, in general, the Demand Duo® is equivalent to two or three tankless water heater units. Consult with a Rinnai Applications Engineer for sizing.

Several considerations are made with sizing the system including your gas supply, demand in gallons per hour (GPH), and thermal rise space requirements. We are here to help you choose the right unit. Consult with a Rinnai Applications Engineer for sizing.


At this time, we don’t recommend this. However, testing is underway for this installation type. Since every commercial job is different, we recommend you contact a Rinnai commercial application engineer to discuss options tailored to your unique situation.

Yes. The CU199 is approved for elevations up to 10,200 feet.

Yes, the CU199 modulates its input based on the Delta T (change in temperature).

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