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Demand Duo Hybrid Water Heater

With the power of a tankless and the storage of a tank, the Demand Duo brings new levels of efficiency to commercial water heating.

Overview of the benefits:

  • The power of a tankless
  • More storage than tank heaters
  • Lasts longer than tank heaters 
  • Keeps up with high peak demand
  • Consistently high output
  • Easier, faster installation than other commercial systems
  • Smaller than other commercial systems 

What’s the fuss all about?

This is a new type of water heating system. Before in the blog, we’ve covered both how tank and tankless water heaters work, but the Demand Duo is unlike both. That’s because it is both. Uhh, let me explain. The demand duo is a tankless water heater mounted to the front of a tank water heater. Water gets heated in the tankless unit and stored in the tank before it’s fed out the outgoing pipe.

This may seem like overkill. You may say “Well if they both just make water hot why would you need to have two water heaters? Surely one is enough.”


Sorry for being blunt, we’re just passionate about the Demand Duo Hybrid Water Heater.

The beauty behind the Demand Duo is that it has all the power of a tankless water heater combined with the ready and stored supply of hot water from a tank water heater. It truly is the best of both worlds. If, of course, we’re talking about the two worlds of tank and tankless water heaters.

How it works:

What’s so unique about the Demand Duo is that it is essentially two water heaters. The strength of the tankless unit is that it can heat water faster and more efficiently than the tank unit. The strength of the tank unit is that it can store already hot water. The tank provides a standing 119 gallons of hot water, and the tankless is able to heat water at 5 gallons per min. And that’s in Minnesota where the groundwater is frigid. So even in Minnesota that’s 300 gallons of hot water an hour, not to mention the 119 gallons of water that’s kept hot by the tank.

The way they’re connected is what makes it work so well and highlights these strengths. When it comes to heating the water, only the tankless is doing the heavy lifting. The tank is just along to store all the hard work that the tankless unit does. The tankless unit heats the water and the tank unit stores it. This is the best of both worlds because tankless units can heat water more efficiently and faster than a tank ever can. The drawback with the tankless unit - obviously - is that there’s no tank. So of course with the Demand Duo, you give the tankless unit a place to store hot water. What we’re left with is a water heating system that combines the unprecedented power and speed of a tankless unit with the storage capacity and readiness of a tank water heater. It’s a simple concept with incredible results.

Because this system is so powerful, it is designed to be used in a commercial environment. Commercial spaces like restaurants, hair salons, large residential buildings, and churches are all great fits for the Demand Duo. Because of its design, it can efficiently provide the upper limits of the amount of hot water a commercial environment needs. If one isn’t enough, then install more depending on your building's needs. You can even get a duo of Duos and blow the competition out of the water! (Sorry, bad joke)

How it compares to other options:

The Duo is smaller and more cost-effective than other options for commercial environments for the same power. Put another way, traditional tank and tankless water heaters might take an entire rack to catch up with the Demand Duo’s power.

Another win with the Demand Duo is how it preserves the life of the tank heater. Commercial heaters fail at a drastically faster rate because of the added use and stress the area of use creates on them. Because of the design of tank water heaters, they put themselves under constant stress - heat stress.

Tank water heaters are made with a burner positioned at the bottom. Whenever the burner is on, it is blasting directly against the bottom of the tank. Over time, this degrades the integrity of the tank and eventually, the tank will need to be replaced due to the heat stress it’s put on itself.

The Demand Duo system avoids this problem. Because the tankless unit does all of the heating, the tank’s burner doesn’t need to do any work. The tank simply acts as storage. And of course, the burner isn’t eroding the tank so the tank is going to last longer. Because of this, the warranty of the Demand Duo is 2x longer than the warranties of most tank water heaters. So the Demand Duo is smaller than other commercially available water heating systems and it lasts longer and it’s under warranty longer than tank water heaters. It’s not looking good for the competition.

By the way, the Demand Duo has even more storage capacity than a regular tank water heater of the same size. This is because on the inside of a normal tank water heater there are all kinds of heating elements, anode rods, and other “guts” inside the tank to help it heat water. As you well know, the Demand Duo doesn’t even use the tank water heater to heat the water. So there’s no need for anything inside the tank except hot water! That means it uses 100% of the storage capacity for hot water while most tank heaters use only 70% for hot water.

How to get one installed and other resources:

This is an ideal water heating system for a school, church, restaurant, kitchen, salon, or really any business or building that uses a lot of hot water. If you’re ready to get a Demand Duo system installed and you’re in our service area, give us a call at 612-712-1105 or click the button right at the top of your screen. You can also fill out a form on our contact page and we’ll reach out to you. Let’s have a chat and find a time to install the Demand Duo for all your commercial needs.

If you’d like to know more about the Demand Duo System from Rinnai, check out these videos. I especially recommend going to their site to see all the different options and features they have for the Duo.

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