Rheem recently introduced its Integrated HVAC and Water Heating System Powered by Tankless Technology, which consists of a tankless water heater matched with a hydronic air handler. (Courtesy of Rheem.)

Move over traditional boilers and water heaters - there’s a new kid in town that can do both your jobs in a much smaller space. Who is this wunderkind? The tankless water heater, which is now being paired with hydronic air handlers in order to provide space heating and endless domestic hot water (DHW) in residential applications.

The tankless space heating system is being targeted directly at the residential heating market, which has traditionally been the domain of forced-air gas furnaces. Tankless space heating systems can usually be retrofitted easily into homes that use forced-air gas furnaces, and their initial cost is often less than a traditional system that requires both a water heater and a boiler or furnace. Combine those benefits with energy efficiency and reported greater levels of comfort, and manufacturers are hoping that contractors will consider adding tankless space heating systems to their line-up.


Earlier this year, Rheem jumped into the tankless space heating market by introducing its Integrated HVAC & Water Heating System Powered by Tankless Technology, which consists of a Rheem tankless water heater matched with a Rheem hydronic air handler. In this system, hot water is circulated through the hydronic air handler to provide warmth and is then recirculated back to the tankless water heater to ensure that no water is wasted.

“Essentially what we’ve done is taken our gas furnace platform and converted that into a hydronic air handler,” said Tim Shellenberger, vice president, research and development, Rheem, Fort Smith, Ark. “The air handler has an identical footprint to our gas furnace, so it’s easy to take out an old gas furnace and put in one of these new tankless systems. What is unique about our system is that it is truly integrated, built by one manufacturer, designed to provide complete whole home air and water comfort.”

The air handler was designed around the tankless water heater, explained Shellenberger, in order to obtain the correct flow rates through the system, which will result in optimal system performance. When sized properly, tankless water heaters are capable of heating a home, as well as providing continuous hot water in any type of climate.

Rinnai’s tankless space heating systems can be retrofitted into virtually any residential application, as long as they are installed as part of an open loop system. (Courtesy of Rinnai.)

“You can really tailor this system closely to the heat loss of a home by simply changing the temperature on the tankless water heater, which you can’t do with a gas furnace,” said Shellenberger. “That is a really unique feature of this system and provides for better comfort, because you get longer run times and less stratification in the house.”

Other benefits for homeowners, he explained, are that the tankless water heater doesn’t take up the space of a traditional tank, and the system is also extremely quiet. In addition, customers will soon be able to choose between the standard tankless water heater and a brand new condensing tankless water heater from Rheem, which will be available later this year.

For the contractor, installation is made easier, because the tankless space heating system only requires one gas line and one vent system, as opposed to separate lines and systems needed for a water heater and furnace (or boiler). In addition, the tankless water heaters offer a new 3/5-inch concentric vent system and integrated condensate collector, all of which are designed to save contractors money on installation costs.

While there is currently no methodology in place for rating the efficiency of these types of systems, Shellenberger noted that the performance of the space heating portion of the system will operate at the efficiency of the tankless water heater. For example, the new condensing tankless water heater is 94 percent efficient, making its air handler 94 percent efficient also.

Rheem tankless water heaters are Energy Star qualified and the Integrated HVAC & Water Heating System Powered by Tankless Technology is protected by a five-year air handler warranty and a 10-year tankless heat exchanger warranty.

According to Rheem, its tankless space heating system is very quiet and doesn’t take up the space of a traditional tank. (Courtesy of Rheem.)


Rinnai started offering its tankless space heating system in 2007, and the company plans to release a redesigned version of the system, which will contain an ECM motor, later this year. “In our system, you can choose either a standard tankless unit or a high-efficiency condensing tankless unit, and then combine it with a hydronic furnace (air handler),” said Tracy Young, product manager, Rinnai.

The hydronic furnace contains a special pump that is designed to work specifically with Rinnai tankless units in order to optimize efficiency. “Our tankless heating system is like a sports car - it ramps up very quickly and efficiently in order to provide large volumes of water that can provide both DHW and space heating,” said Young.

The Rinnai system gives priority to DHW so that everyone in the home can obtain the hot water they require. To do this, the system monitors the flow going to and from the tankless unit, and if the system senses a drop in volume, it will turn off the blower so that cold air is not blown into the house. Once the volume of hot water returns to normal, the system will turn the fan back on in order to satisfy the space heating needs of the occupants. Young noted that the occupants in the home won’t even miss the space heating during the time that the system is giving priority to DHW.

Boilers and furnaces usually have a long lifespan, and Young noted that tankless space heating systems are durable as well. “With the specialized pump that we have, we are able to pull hot water from the tankless unit into the furnace, and as the blower comes on, it extracts a good portion of that heat off that water before it returns to the tankless unit. It runs in a similar way to a traditional furnace, which - if properly sized - will probably run five or 10 minutes before it turns off.”

Tankless space heating systems can be retrofitted into virtually any residential application, as long as they are installed as part of an open loop system - meaning they are open to the atmosphere, which in this case, would be the fixtures in the house. Tankless water heaters do not carry a boiler safety rating, so they cannot be installed in a closed loop system, such as one with radiant in-floor heat, radiators, or baseboards. “Certain states have low-lead standards, and while our tankless water heaters meet low-lead standards, the furnace is not yet low-lead, though we plan to address that issue soon,” said Young.

Rinnai’s tankless units come with a 10-year heat exchanger warranty, five-year parts, and one year of reasonable labor. The furnace comes with a five-year parts and one-year reasonable labor. “This system is great for homeowners, because they get the advantage of endless hot water and better efficiency of heating that water; plus, it provides heat for the entire home. It’s an ideal setup,” said Young.

Publication date: 10/25/2010