Condensing Boiler Optimization

Russ Landry, Neal Ray, Martha Hewett

Field study to quantify how operating conditions impact the installed energy savings of condensing boilers and determine the potential for optimization through low-cost upgrades.

Condensing boilers are one of the most promising natural gas technologies for reducing Minnesota commercial energy use, but their efficiency is extremely sensitive to operating conditions- especially the temperature of the water entering the boiler.

An effective condensing boiler retrofit often calls for modifications in building controls and piping. Many installed systems achieve as little as half of their theoretical savings, because the optimal conditions for condensing boilers would cause a standard boiler to fail prematurely. 


This field study will evaluate the realized operating efficiency of condensing boilers used to space heat commercial buildings in Minnesota. The project will monitor systems at twelve representative buildings over several months to determine the efficiencies achieved and the potential for optimization through low to moderate-cost upgrades.  Findings could help increase the energy savings of each installation. Staff will use field results and industry interviews to recommend future program strategies (e.g. additional rebates if technical requirements for optimal system application of condensing boilers are met).


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


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Project Info


Project Description

(PDF, 0.32 MB)

CEE Contact:

Russ Landry, P.E.