A Review of Wood and Pellet Stove Efficiency Ratings; More Manufacturers Posting Verified Efficiencies

As of May 15 2020, all certified wood stoves, boilers and furnaces are required to have a tested efficiency.  This blog discussed the period leading up to May 15, when some heaters had verified efficiencies and others did not.

April 10, 2020 - The number of wood and pellet stoves with verified efficiency numbers on the EPA’s list of certified wood and pellet stoves is soaring as we approach the May 15 deadline, when all stoves in production are required to post their efficiency.  This gives those consumers who really care about verified efficiency numbers many more options. There are now 296 stoves, nearly half of all stoves, that have verified, actual efficiency numbers.  The EPA list of stoves is the definitive source for efficiency numbers as most most stove company websites use exaggerated, misleading efficiencies.

Among the 296 stoves with actual efficiencies, hybrid, catalytic and pellet stoves are the most efficient, averaging 77% efficient for cat stoves and 78% for hybrids.  The average non-catalytic stove is 71% efficient and the average pellet stove 74% efficient.  Pellet stoves also have the greatest range, from 58 to 87% efficiency, a 29 point difference with an average of 74%. Consumers should be aware of which pellet stove they buy.

Consumers should should be especially aware that many stove companies issue Certificates claiming their stoves qualify for the federal tax credit, even though they are far below the required efficiency.  The IRS requires a thermal efficiency rating of 75% but in the absence of any apparent IRS oversight, companies are claiming stoves with efficiencies as low as 59% qualify.  Jotul claims all of their stoves qualify, including their F370 listed at 66% efficiency.  Hearth & Home Technologies claims their Quadra-Fire Classic Bay 1200 qualifies at 63% efficiency.  Neither company replied to AGH inquiries.  The industry association, HPBA, would not comment on how manufacturers should calculate efficiency for the tax credit.

Kuma now holds the distinction of having the highest rated efficiency of any wood stove at 84%, tested with crib wood and the highest tested with cordwood, at 81%.  Enerco, a Cleveland Ohio compnay and ExtraFlame, an Italian company, have the highest rated pellet stove efficiencies at 87%.  Enerco's model, sold under the Cleveland Iron Works label, is a budget model sold in big box stores, as are the PelPro stoves that are above 80% efficiency and have a solid reputation for durability.

The EPA dropped the estimated default efficiency numbers on their list of certified stoves in 2015, an acknowledgement that those default numbers were both inaccurate and not helpful to consumers. (They used to assign 63% efficiency to non-cat stoves, 72% to catalytic and 78% to pellet stoves.) As of 2015, the EPA does not maintain or endorse any efficiency default numbers.

The Alliance cautions consumers against relying on stove efficiency claims posted on manufacturers websites. Most manufacturers post efficiencies numbers using a variety of non-standardized calculations. Virtually all post efficiencies using the European lower heating value (LHV) standard.  A 75% efficient stove using LHV would be about a 70% efficient stove using HHV if the wood was at 20% moisture content. (See this Wikipedia page for more about the difference between LHV and HHV.)

Even if a company has a verified, third party efficiency value on the list of EPA certified wood stoves, many companies will continue to list efficiency values far higher on their own websites, where most consumers get their information.    Only a handful of companies, including Blaze King, Kuma, Seraph, Travis and Woodstock Soapstone, provide the same efficiency number on their website as the independent lab reported to the EPA.  Fewer companies list their official EPA test report on their website next to their product, as required by the EPA.  Exceptions include J.A. Roby, Kuma, and Jotul.  Click here for more on brands that consumers can trust.

The EPA started to require stoves to be tested for efficiency in May of 2015, far later than their European counterparts.   Stoves that were tested and certified before May 2015 did not have to disclose their efficiency until they are required to test again, which will be 2018-2020 for many stoves.  Some of the stoves listed here were done so voluntarily by manufacturers, not because they were required to.  Pellet stove companies in particular appear to be least willing to share verified efficiency numbers with consumers, possibly because their efficiency numbers are lower than the could be.

The EPA began issuing a voluntary hangtag to stoves that meet the 2020 emission standards early, disclose their actual efficiency and meet a variety of other disclosure requirements.  Many of the stoves on the list above will be eligible to display that hangtag on the showroom floor and the Alliance for Green Heat urges consumers to consider buying stoves that display the hangtag.  Stoves sold by Blaze King, Travis and Unforgettable Fire are now approved to display this hangtag and more companies will be approved soon.

How important are efficiency listings?

Tested efficiencies of wood stoves give an indication of how efficient the stove can be when it is operated well with seasoned wood.  Efficiency and emission numbers achieved in a lab under optimum conditions are likely the best numbers that stove can achieve, not an expected average that a consumer will get.

Unseasoned wood that is over 25% moisture content will dramatically lower efficiency.  More important than a 5% difference in tested efficiency is burning your stove with seasoned wood and with enough air to the firebox.  Even the most clean and efficient stove can be polluting and inefficient if it is not operated well.

For pellet stoves, the lab tested efficiency numbers are more representative of efficiencies you get at home, assuming you keep the stove clean.  A dirty pellet stove that has not been serviced for more than 6 months is likely to get lower efficiency.

Wood Stoves with Verified Efficiencies

The non-catalytic stoves on this list range from 60% to 77% efficiency, the narrowest efficiency range of any class of stoves.  Catalytic and hybrid stoves range from 63% to 84% efficiency.  Pellet stoves range from 58% to 87%, the widest efficiency range among different types of stoves.

The Vermont Castings Encore
is a hybrid stove that does not
have a verified efficiency on
the EPA list, but they use one
on their showroom hangtag.

Some companies are claiming verified efficiencies on their showroom hangtags but it is unclear if these are actually verified, HHV numbers.  Vermont Castings, for example, and the hangtag in the showroom shows their purported tested efficiency but they have apparently not provided the a verified efficiency to the EPA for the list of certified stoves.

Pellet Stoves with Verified Efficiencies 

Virtually all companies that make pellet stoves now have some with verified efficiencies on the EPA list, a major shift since May 2015.  Italian company Extraflame currently produces the two most efficient pellet stoves on the EPA list, at 87% and 85%.   Aside from Extraflame, 14 other models have efficiencies above 80%.

The average efficiency of a pellet stoves is about 74% HHV,  but many popular pellet stoves are between 58 and 65% efficient. Of the nearly 170 stoves with actual efficiencies, the only ones under 60% or over 85% are pellet stoves.

For more background on this issue, see:

EPA Begins Listing Actual Stove Efficiencies

The Case for Minimum Efficiency Standards for Stoves

EPA Lists Efficiencies for Outdoor Wood Boilers

4 Reasons Why Wood and Pellet Stove Efficiencies are Usually Unreliable

Pro-wood heating group says EPA regulations reasonable and will help industry grow

The Alliance for Green Heat welcomed the release of proposed EPA regulations on residential wood and pellet heating equipment, saying that new, stricter emission standards “will help America embrace wood and pellet heating as a vital renewable energy that can help drastically reduce fossil fuel consumption.”

More than 10 million American homes heat with wood and pellets, ten times more than solar and geothermal combined, according to data from EIA and the US census. “We can harness the huge demand for this type of renewable energy if the stoves and boilers are clean enough,” said John Ackerly, President of the Alliance for Green Heat. “We believe the emissions numbers released by the EPA today are reasonable and achievable and will help the wood stove industry grow and thrive in coming decades,” Ackerly continued.

The proposed rule has few surprises in terms of emission numbers. Virtually all the key numbers were included in draft proposed rules shared with industry, states and non-profits during 2013. But the proposed rule does reflect the much stricter numbers the EPA developed after states and air quality agencies intervened in 2012. Previously, the EPA was considering 2.5 grams per hour to be the strictest level for wood and pellet stoves. But last year, the EPA floated a 1.3 grams per hour for all pellet and wood stoves and that is the number that was released today.

The EPA is proposing that wood and pellet stoves initially meet a 4.5 grams per hour standard, and then meet a much stricter standard of 1.3 grams per hour 5 years after promulgation. Alternatively, the EPA proposes a 3-step process of going to 2.5 grams per hour after 3 years and then 1.3 grams an hour after 8 years.

Similarly, the EPA is proposing two options for furnaces and boilers. The first would establish strict emission limits after 5 years, and the second would have an intermediate step after 3 years, and then the stricter standard after 8 years. Initially, warm air furnaces would only be held to 0.93 lb/MMBTU, whereas hydronic heaters would be held to 0.32. Ultimately, both would need to reach 0.06 lb/MMBTU either 5 or 8 years after promulgation. It is widely anticipated that industry will advocate for the 3-step process and that EPA would be open to this as well.

The EPA’s press release said that “when these standards are fully implemented ... [c]onsumers will also see a monetary benefit from efficiency improvements in the new woodstoves, which use less wood to heat homes.” However, the EPA decided not to include any efficiency standard, leaving open the possibility that some very inefficient units may remain on the market. Wood and pellet heating appliances are the only HVAC equipment without minimum efficiency standards.

Both efficiency and CO would have to be recorded and reported under the new proposed rules. To avoid logjams in testing to the new standards, the EPA is proposing “to allow ISO-accredited laboratories and ISO-accredited certifying bodies to increase the availability of laboratories and certifiers.” 

The EPA is scheduling a public hearing on these regulations in Boston on February 26. Interested parties should register by February 19 at http://www2.epa.gov/residential-wood-heaters if they want to make public comments. Each person will be limited to 5 minutes. The public has 90 days to comment on the regulations after they are posted in the Federal Register, which is expected to happen in the next week or two. 

The proposed rule does offer an unusual glimpse into disagreements between the EPA, the Small Business Agency (SBA) and the Office of Budget and Management (OMB).  In the Panel Report, the “SBA and OMB recommended that the EPA not move forward with proposed emission limits for pellet stoves, indoor hydronic heaters, biomass pellet stoves, masonry heaters.” The EPA however rejected this recommendation and provided a sound basis for their proposal to include pellet stoves, all hydronic heaters and masonry heaters.

The SBA and OMB also recommended that the NSPS only cover parts of the country where wood smoke pollution was high. They suggested that states and regions where wood smoke is not high be allowed to issue their own regulations and consider voluntary standards. The EPA chose to highlight and counter these recommendations in its proposed rule, showing that they have considered these options but found they were not justified.

The Alliance for Green Heat is a non-profit consumer advocacy organization that fights for cleaner and more efficient wood and pellet heating to help households affordably switch to a renewable heating fuel.

For the full regulations see: http://www2.epa.gov/residential-wood-heaters

A summary of the regulations prepared by EPA, without emission numbers, can be found here:
www2.epa.gov/sites/production/files/2013-12/documents/proposed_wood_heater_nsps_overview_fact_sheet_1.pdf