The most energy-efficient boilers in production as of 2015 are produced by Westinghouse and HTP, according to the Air Conditioning, Refrigeration and Heating Institute. Models from these companies achieve an average fuel use efficiency rating of 96.3 percent.
Both of the most energy-efficient boilers on the market are gas-burning models that utilize a forced-draft ventilation system for additional efficiency. Forced-draft boilers use a fan to bring external air into the unit for combustion, improving the overall combustion efficiency of the boiler. While only Westinghouse and HTP manufacture boilers that achieve 96 percent efficiency or more, many manufacturers produce similar boilers rated at 95 percent efficiency.