EPA Lists Efficiencies of Certified Boilers from 39% to 88%

Updated: Nov. 2016

In April 2014, when the EPA began posting efficiencies for outdoor wood and pellet boilers, there were only 40 units.  The average outdoor wood boiler was 63% efficient, and the average pellet boiler was 74% efficient and the most efficient of all was 82% efficient.

Since the spring of 2014, the EPA implemented emissions standards for outdoor and indoor boilers, otherwise known as hydronic heaters, and the number of units and their efficiencies have risen dramatically.  As of November of 2016, there are 131 certified units and half the list, 61 units, have efficiencies higher than 82%, the highest of any unit in 2014.

The rapid rise in efficiencies and lowering of particulate matter emissions is evidence that the new EPA regulations have had significant positive impact on boiler technology.  However, the move came at time of low oil and gas prices, and warmer than average winters which has depressed the market for boilers.  And, while the prices of many indoor pellet boilers remained stable, the regulations raised the prices of domestic outdoor cord wood boilers that had to be redesigned to meet the new standards.

The rapid rise of highly efficient boilers is mainly the result of indoor, imported pellet boilers joining the EPA list. The main industry association representing outdoor wood boilers, HPBA, fought against test methods that would allow indoor boilers and furnaces to be listed here, but efforts from New York state and elsewhere prevailed.

The lowest listed efficiency is Marway Welding’s Phase 2 – 200 at 39%.  Another outdoor boiler has 47% efficiency. In all, there are 19 units that are 65% efficient or lower.  All of the units that are over 80% are pellet units, and of the 19 units at 65% or lower, all but 2 are cordwood. Unlike stoves, where pellet stoves are often less efficient than wood stoves, the generalization that pellet boilers are more efficient than wood ones is true.

The posting of these efficiency numbers was welcomed by the Alliance for Green Heat who has long advocated for consumers having access to reliable efficiency data.  The listing of reliable efficiencies makes hydronic heaters the first class of wood heating appliances to provide efficiencies to the general public for all of the certified units.  It will take years for the public to get reliable efficiencies on most wood and pellet stoves, as most manufacturers have been unwilling to share that information with the public until it is required by law to do so. 

The saga to provide consumers with such data has taken many twists and turns.  In 2011, the EPA removed efficiency numbers from their list for boilers that were in the 90% range after state regulators questioned their accuracy.  Industry continued to advertise outrageously high efficiencies, even after the EPA sent letters to the companies asking them to desist. Scott Nichols, who sells European indoor boilers that were previously not part of the EPA voluntary program, is one of few to write about these issues that have faced EPA and the boiler industry.



Unregulated outdoor boilers plague many states and provinces and public funds have been used in Vermont and Connecticut to pay people to give up these boilers.  The need to retire these boilers is the greatest in Michigan, Minnesota and Wisconsin, but public opinion and legislatures in those states have protected the outdoor boiler industry.  The province of British Columbia announced some of the strictest policies, requiring certified outdoor boilers to be set back 40 meters (131 feet) from property lines and then banning the use of uncertified units after 2026 if they are not 80 meters from the property line.