U.S. Department of Energy - Energy Efficiency and Renewable Energy

Federal Energy Management Program

New and Underutilized Technology: Condensing Boilers

The following information outlines key deployment considerations for condensing boilers within the Federal sector.


Condensing boilers are commercial boilers that are highly efficient due to their designed ability to extract heat from flue gas moisture.


Condensing boilers are appropriate for housing, service, office, research and development, schools, and hospital applications.

Key Factors for Deployment

FEMP designated product specifications require Federal agencies to purchase gas hot water supply boilers with an efficiency level of at least 94% if they:

  • Have inputs between 300,000 and 12,500,000 Btu/h.
  • Have at least 4,000 Btu/h per gallon of water stored.
  • Are intended for heating potable water.

This effectively requires a condensing boiler.

Condensing boilers are a good fit when the water entering the boiler is cold enough. Many boilers for space heating have return water temperatures too high for the flue gas to condense. Many have an outdoor reset that raises the water temperature when the outdoor temperature is cold (i.e., when the most heating occurs). If boilers are used to heat domestic hot water (i.e., cold water from the city mains), then that would be a good application for condensing boilers.

Condensing boilers are also possibly appropriate for radiant floor heating or thermal displacement ventilation where lower temperatures can be used.

In new installations, air handlers and coils can be sized to use cooler water, but must be sized larger. This makes the unit more expansive, so life-cycle cost effectiveness calculations should be made.

Ranking Criteria

Federal energy savings, cost-effectiveness, and probability of success are ranked 0-5 with 0 representing the lowest ranking and 5 representing the highest ranking. The weighted score is ranked 0-100 with 0 representing the lowest ranking and 100 representing the highest ranking.

Federal Energy Savings Cost Effectiveness Probability of Success Weighted Score
5.0 3.0 4.5 86