Wednesday, April 9, 2014

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

Updated: July, 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, were 82% efficient.

Since the spring of 2014, the EPA implemented emissions standards for outdoor and indoor boilers, and the number of units and their efficiencies have risen dramatically.  As of July of 2016, there are 72 certified units and more than 2 dozen are higher efficiency than any unit in 2014.

The rapid rise of highly efficient boilers is mainly the result of indoor, imported pellet boilers joining the EPA list.

The lowest listed efficiency is Marway Welding’s Phase 2 – 200 at 39%.  Another boiler has 47% efficiency.

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.  It may 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 for boilers that were in the 90% range after state regulators questioned their accuracy.  Scott Nichols, who sells European indoor boilers that are not part of the EPA voluntary program, is one of few to write about these issues that have faced EPA and the boiler industry. 

The EPA requested outdoor boiler manufacturers to stop using the discredited high efficiency numbers in their advertising, but few stopped using them, leading to a letter from the EPA in 2013, which strongly urged manufacturers to stop using the efficiency numbers.  The Alliance for Green Heat reported on that development and documented numerous cases where outdoor boiler manufacturers were engaging in other misleading advertising practices


  1. Note that you have to burn twice as much wood in the 39% boiler for the same heat output as the 78% boiler. If both boilers had the same particulate (PM) emissions factor in terms of grams of particulate per kilogram of fuel (g/kg), the inefficient boiler would have twice the emissions measured in g/h at the same heat output, or in lb/MMBtu at any heat output.

  2. Nice post on outdoor boilers. I would like to know about the proper maintenance of boilers and their scheme. I came to know about UK boiler scheme from
    Azko Energy . It was helpful..