Hydronic Heating Retrofits for Low-Rise Multifamily Buildings: Boiler Control Replacement and Monitoring

J. Dentz, H. Jr, K. Varshney

Research output: NRELSubcontract Report


The ARIES Collaborative, a U.S. Department of Energy Building America research team, partnered with NeighborWorks America affiliate Homeowners' Rehab Inc. (HRI) of Cambridge, Massachusetts, to study improvements to the central hydronic heating system in one of the nonprofit's housing developments. The heating controls in the three-building, 42-unit Columbia Cambridge Alliance for Spanish Tenants housing development were upgraded. Fuel use in the development was excessive compared to similar properties. A poorly insulated thermal envelope contributed to high energy bills, but adding wall insulation was not cost-effective or practical. The more cost-effective option was improving heating system efficiency. Efficient operation of the heating system faced several obstacles, including inflexible boiler controls and failed thermostatic radiator valves. Boiler controls were replaced with systems that offer temperature setbacks and one that controls heat based on apartment temperature in addition to outdoor temperature. Utility bill analysis shows that post-retrofit weather-normalized heating energy use was reduced by 10%-31% (average of 19%). Indoor temperature cutoff reduced boiler runtime (and therefore heating fuel consumption) by 28% in the one building in which it was implemented. Nearly all savings were obtained during night which had a lower indoor temperature cut off (68 degrees F) than day (73 degrees F). This implies that the outdoor reset curve was appropriately adjusted for this building for daytime operation. Nighttime setback of heating system supply water temperature had no discernible impact on boiler runtime or gas bills.
Original languageAmerican English
Number of pages54
StatePublished - 2014

Bibliographical note

Work performed by ARIES Collaborative, New York, New York

NREL Publication Number

  • NREL/SR-5500-62629

Other Report Number

  • DOE/GO-102014-4493


  • boiler controls
  • Building America
  • EE
  • EE
  • energy efficiency
  • hydronic heating
  • indoor temperature cutoff
  • multifamily
  • outdoor reset
  • residential
  • residential buildings
  • retrofit
  • setbacks


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