Condensing Boiler Optimization

Russ Landry, P.E., Neal Ray, Martha Hewett — Jan 2013

Project update

Field monitoring wrapped up in fall 2014 and the project team is now identifying measures to provide savings and analyzing potential savings. Full project update

Why This research is Needed

Condensing boilers are one of the most promising natural gas technologies for reducing Minnesota commercial energy use. However, many newly installed systems only achieve a fraction of their expected energy savings.

The efficiency of condensing boilers is extremely sensitive to operating conditions — in particular the temperature of the water entering the boiler. Often, an effective retrofit requires modifications of the boiler system controls and/or piping because the equipment and controls are based on standard boiler operating conditions, which are different than the low temperature and load conditions needed for condensing boilers to perform best.

Project Process and Expected Outcomes

This field research aimed to quantify how operating conditions impact the installed energy efficiency of commercial condensing boilers in Minnesota, and to determine the potential for optimization through enhancements to utility efficiency program.

The project team monitored systems at 12 representative buildings over several months to determine the achieved efficiencies and potential for optimization through low-cost upgrades. To do this the team analyzed the efficiencies at which the boilers were found to be operating, identified measures to provide energy savings, and calculated potential savings. The findings could help increase the installed energy savings of condensing boilers. The team also conducted industry interviews, which were used along with field results to recommend future program strategies in a draft final report.

This project supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through the Conservation Applied Research and Development (CARD) program. And with co-funding by CEE in support of its nonprofit mission to advance research, knowledge dissemination, and program design in the field of energy efficiency.


Photo courtesy of DOE/NREL. Diagram courtesy of

Project Info


The final report will be released upon approval by DER.

To evaluate the realized operating efficiency of condensing boilers used to space heat commercial buildings in Minnesota.

Utility Implementation
Full scale rebate programs have been successful for condensing boilers, and this study recommends specific utility program enhancements and initiatives to increase this success.

This project included an initial local market study, a field study of 12 commercial buildings in Minnesota with condensing boilers that covered the full range of heating season conditions, detailed analysis of installed efficiency and potential improvements, and a survey of local boiler industry professionals.

Non-Energy Benefits
Often the issues contributing to reduced operating efficiency also accelerate wear on the boilers and this can lead to other operational problems.


MN Department of Commerce, Division of Energy Resources

CEE Contact
Russ Landry, P.E.

PRESENTATION: Replacement Condensing Boilers

Project Description (PDF)