Retrofitting Integrated Space & Water Heating Systems

Ben Schoenbauer; Dave Bohac, P.E; Martha Hewett; Alex Haynor; Corinne Wichser

Lab tests and field assessments of integrated domestic water and space heating system performance and energy savings.

Improvements in building envelope and insulation technologies have reduced the energy required to heat houses. Therefore, despite efforts to reduce water heating loads, the relative size of domestic hot water energy use has increased. One emerging solution is integrated domestic hot water and space heating systems, which provide both heating loads with a single heating plant. These systems, called dual integrated appliances (DIA) or combination systems, can also eliminate safety issues. However, they have a small market share because of their higher installation costs, inconsistent performance, and uncertain efficiency in a real-world setting. 


To reduce these barriers, this project is characterizing the installed performance of over 300 DIA systems with monitoring in 20 Minnesota homes and documenting the subsequent energy savings. This research is focused on DIA systems with water heater and boiler heating plants teamed with forced air distribution space heating systems. 

CEE staff also monitor key system parameters to understand variations from expected performance and to identify improved system designs. The project will develop a set of standard specifications to ensure that the systems satisfy space and hot water loads and achieve expected efficiency with low installation costs. Research results will also determine installation costs and potential cost reductions that could occur with widespread installation. 

Watch these animations or download this webinar to learn more about the systems.


This project is supported by Building America, as part of the NorthernStar project team.


I have a Navien tankless boiler awaiting selection of variable speed air handler to complete a combined htg system. Can you share products and guidance for installation that I can use to communicate best practices and products to installers? Thx for recent presentation at B4 Illinois!
Exciting research. I am looking forward to the publication of the results.

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