Friday, January 31, 2014

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


  1. Lamppa Manufacturing Inc. posts an actual copy of the efficiency and emissions testing done by Intertek on the Kuuma Vapor-Fire 100 and 200 furnace models right on it's website.

  2. None of the efficiency rating mean much under normal operating conditions. Residents close the dampers at night then the stove smokes out neighbours. They recharge the stove in the morning then leave it smouldering all day while they are at work and smoke pours into neighbours' homes. Also the number of people who burn green wood is surprising. Hopefully I will never find anyone burning wood within a block of my home.

    Alan Smith Canadian Clean Air Alliance

    1. While I understand the frustration over the lack of real world relevancy of EPA mandated testing (who burns test fuel in a perfectly controlled laboratory), I resent the inference that all wood burning stoves smoke in the way you present. Kimberly and Katydid by Unforgettable Fire have a reputation for not doing this due to our gasification/reburner technology. In fct I would challenge you to prove one of our stoves is even running in your neighborhood, unless some idiot is burning green wood, even then I challenge you to think about the dangerous and environmentally damaging comparison of just one gals line explosion......think dude think!

    2. Most of this page is not at al applicable to NZ for several reasons.
      1 - Pellet fires and wood burners in NZ have to be tested and meet criteria before being allowed to be installed.
      2 - Pellets in Nz are manufactured under strict guidelines. They are very very low moisture content, manufactured from non-treated wood and are normally waste product from saw mills adding to their greenness.
      3 - We are NZ, the EPA doesn't have any say here and what they are doing has little or no effect on us. Your articles around pellet fires don't belong in NZ as the scene here is totally different.

  3. If many European stove manufacturers meet the more stringent LHV standard, why is it so difficult to purchase them in North America? Wouldn't increased availability encourage N.A. manufacturers to step it up and make more efficient products?

    T. Corneil, conscientious consumer

    1. I am starting to check out European stoves, need a new stove stove soon. Someone recommended a Piazetta - about 90% efficency rating, would like to see if anyone actually owns one.

  4. Why would you suggest they look at European stoves and look past Seraph?

  5. With the winter months rapidly approaching, I’ve been researching pellet stoves Bucks PA to find a model that would work well for my home. One contactor insisted that we would only need the stove setup in our basement, and he could vent the heat throughout our home. I’m worried that we’ll be spreading the heat too thin, but I’d love some feedback from anyone who has a stove setup in their basement.

  6. Today’s wood stoves burn 50 percent more efficiently than traditional wood stoves and produce 70 percent less particle pollution indoors and outdoors.

  7. The EPA list is NOT to be confused with wood burning stoves that qualify for the Biomass Credit. Many of the stoves on the EPA do not an efficiency rating percentage in the appropriate column. No Biomass Credit Qualifying list from the government exists. Only comes from manufacturer. Problem - a lot of conflicting information. Especially from manufacturer reps. It all depends who you talk too. Outdated info on internet that has been taken down.