Building America Case Study: Evaluation of Residential Integrated Space/Water Heat Systems, Illinois and New York (Fact Sheet)

Stacey Rothgeb, T. Kingston, H. Vadnal, S. Scott, D. Kalensky

Research output: NRELFact Sheet


This multi-unit field demonstration of combined space and water heating (combi) systems was conducted to help document combi system installation and performance issues that needed to be addressed through research. The objective of the project was to put commercialized forced-air tankless combi units into the field through local contractors that were trained by manufacturers and GTI staff underthe auspices of utility-implemented Emerging Technology Programs. With support from PARR, NYSERDA and other partners, the project documented system performance and installations in Chicago and New York. Combi systems were found to save nearly 200 therms in cold climates at efficiencies between about 80% and 94%. Combi systems using third-party air handler units specially designed for condensingcombi system operation performed better than the packaged integrated combi systems available for the project. Moreover, combi systems tended to perform poorly when the tankless water heaters operating at high turn-down ratios. Field tests for this study exposed installation deficiencies due to contractor unfamiliarity with the products and the complexity of field engineering and system tweakingto achieve high efficiencies. Widespread contractor education must be a key component to market expansion of combi systems. Installed costs for combi systems need to come down about 5% to 10% to satisfy total resource calculations for utility-administered energy efficiency programs. Greater sales volumes and contractor familiarity can drive costs down. More research is needed to determine howwell heating systems such as traditional furnace/water heater, combis, and heat pumps compare in similar as-installed scenarios, but under controlled conditions.
Original languageAmerican English
Number of pages2
StatePublished - 2014

Bibliographical note

Work performed by Partnership for Advanced Residential Retrofit (PARR), Chicago, Illinois

NREL Publication Number

  • NREL/FS-5500-62496

Other Report Number

  • DOE/GO-102014-4475


  • Building America
  • combi
  • combo space heating
  • Parr
  • residential
  • residential buildings
  • water heating


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