Replacing a traditional tank water heater with the Rinnai Demand Duo® Commercial Hybrid System helped an Applebee’s Restaurant take on the demands of business.

Food Service

O'Fallon, Missouri

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Spend a day in the life of restaurant manager for your neighborhood’s popular bar and grill and you’ll see what it’s like to serve hundreds of hungry customers looking for a satisfying meal. To get the job done, your staff relies heavily on the building systems to support the restaurant’s basic needs like heating, cooling and plumbing. But what if these systems fail you?

For the Applebee’s Restaurant in O’Fallon, Missouri, this unfortunate situation was a reality. The restaurant’s traditional tank water heater, a 100-gallon model with 399,000 BTU, failed and in return, put them at risk for failing to meet the customers’ needs. The restaurant turned to Rinnai for an innovative water heating solution.


To help the restaurant serve its customers with peace of mind, Rinnai recommended its Demand Duo®, a commercial hybrid water heating system that combines Rinnai’s 199-BTU, ENERGY STAR® certified C199 condensing commercial tankless water heater with a durable 119-gallon tank. Months after installation, this system has proven to be the restaurant’s saving grace and it continues to meet every need with its high-performing benefits.

The installation on the Rinnai Demand Duo was straightforward and simple. The unit has been supplying hot water for six months. It’s proven that it can meet every need of the facility, even on the busiest days.

— Rich Graft, Installer at G&S Service and Repair

The Rinnai Advantage

  • Endless supply of hot water
  • The perfect solution for direct replacement of most traditional standard and high efficiency commercial tanks
  • Multiple venting options (concentric, two pipe, room air, common vent)
  • Assembled with individually certified components
  • Easy and cost effective maintenance – all parts replaceable

High Demand Meets High Performance

The restaurant’s water heating system needs to keep pace with every request – from short-period, high-spike draws to a supply that’s ready to go the distance, day in and day out.


The Applebee’s Restaurant now experiences the high-performing benefits of Rinnai’s Demand Duo®, a unique tank-tankless solution that combines a 119-gallon tank with a C199’s heat exchanger technology that provides gallons of hot water at the moment it’s needed.


“The installation on the Rinnai Demand Duo was straightforward and simple,” said Rich Graft, Installer at G&S Service and Repair. “The unit has been supplying hot water for six months. It’s proven that it can meet every need of the facility, even on the busiest days.”


Internal testing showed that the Demand Duo® system on average produces 338 gallons of hot water in the first hour, compared to a 
standard efficiency tank’s 248 and a high-efficiency tank’s 315. For the restaurant, this high-performing difference was the much needed solution for the business and its customers.

The Rinnai Advantage for Demand Duo® Hybrid Commercial Water Heating System

  • Warranty: 6-year heat exchanger / tank, 5-year parts and up to 2 years labor*
  • Built standard with C199 Commercial Tankless Water Heater
  • Commercial ENERGY STAR® certified with 96% Thermal Efficiency
  • Ultra Low NOx compliant
  • 199,000 BTU
  • First Hour Rating: 338 gal / Recovery: 231 gal (@ 100°F ΔT) ‡
  • Ability to install multiple Demand Duo® Commercial Hybrid Water Heating Systems together to create redundancy
  • Ability to tie into a building management system with the DPS/MIS accessory

The Result

In the end, Rinnai’s Demand Duo™ provided the restaurant’s 14 fixtures, including lavatory faucets, hand and bar sinks, compartment sinks, a pre-rinse faucet and a mop basin faucet, with endless, on-demand hot water so that it was never at risk for failing to meet the customers’ needs, rather setting it up to exceed them.


“Since the installation, the Demand Duo has been working great,” said Dave Burch, General Manager at Applebee’s.

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