Friday, January 31, 2014

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

Updated on October 14, 2015

More stove manufacturers are posting third party verified efficiency numbers on the EPA’s list of certified wood and pellet stoves, giving those consumers who really care about verified efficiency numbers more options. However, there are still only 52 stoves from fourteen companies who post the verified efficiency of at least one of their stoves: Blaze King, Boru Stoves, Enviro, Kuma, Jotul, Ningbao Hongsheng Fireplace, Pacific Energy, Pleasant Hearth, Quadrafire, Regency, Seraph, Travis, Unforgettable Fire and Woodstock Soapstone.

Four companies provide the efficiencies of virtually all of their stoves to consumers: Blaze King, Jotul, Kuma Stoves and Seraph.  The Alliance for Green Heat commends those companies for their transparency.  Kuma now holds the distinction of having the highest rated efficiency of any stove, at 84%, which is generally regarded as nearly the highest that any wood or pellet stove can go. Jotul deserves recognition as well for showing leadership in voluntarily disclosing efficiencies for 14 stoves, more than any other manufacturer.  They also make the F55 which at 76% efficiency is the highest efficiency non-cat stove on the list.

For the first time, the EPA dropped the default efficiency numbers on their list of certified stoves, an acknowledgement that those default numbers were both inaccurate and not helpful to consumers. As of 2015, the EPA does not maintain or endorse any efficiency default numbers, and manufacturers that use them may be doing so because their stoves are less efficient that the now defunct 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, which has been used by industry for the federal wood and pellet stove tax credit, as opposed to the higher American heating value (HHV) standard used by the EPA. A 75% efficient stove using LHV would be about a 66% 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.)

 The average non-catalytic wood stove on this list is about 72% efficient and the average catalytic stove is probably around 80%.  This list in only a fraction of stoves and once all stoves are added in, the average efficiency of non-cats is likely to drop significantly.  The list has a majority of catalytic stoves on it and that efficiency may be representative of that class of stoves.

The EPA has just started to require stoves to be tested for efficiency.  Stoves that were tested and certified before May 15 do not have to disclose their efficiency until they are required to test again, which will be 2018-2020 for many stoves. Most 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 low.

The EPA began issuing a voluntary hangtag, akin to a "green label" to stoves that disclose their actual efficiency and meet the stricter 2020 emission standards.  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.

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 likely to be 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.  Unfortunately, none of the large pellet stove manufacturers have publicly released actual, third party tested efficiency numbers.  And many pellet stoves may only be between 50 and 60% efficient and it is very difficult to know which are which.

Wood Stoves with Verified Efficiencies

There are now fourteen manufacturers posting verified efficiency numbers on the EPA list. The non-cats range from 65 - 76% efficiency and the catalytic and cat/hybrid stoves range from 75 - 84% efficiency. These are all HHV numbers and substantially above the old 63% HHV EPA default efficiency value for non-cat stoves on the EPA list. (HHV numbers are approximately 6 - 9 points lower than LHV.  So a 70 - 82 HHV stove, like those in the EPA list, would be 76 - 90% LHV.  Any stove that is listed above 85% is almost certainly listed using the European LHV efficiency standard.)

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 Stove with Verified Efficiencies 

As of July 2015, there are only two pellet stove companies with a verified efficiency on the EPA list - Seraph Industries and Ningboa Hongsheng Fireplace.  None of the major manufacturers of pellet stoves have been willing to share actual efficiency numbers with the customers or potential customers, to our knowledge.  Ningboa has a very impressive 81% efficiency and is listed at $1,500 retail, making it one of the highest efficiency stoves in the US. The Illinois based company, Seraph Industries, had their stoves certified after testing by Intertek labs, which verified 78% HHV efficiency.  The average efficiency of US made pellet stoves is probably about 70% HHV, based on several third party studies.

Seraph's website had also posted only their LHV number, but recently changed to also include their HHV numbers.  Almost all stove manufacturers only list their LHV efficiency and do not inform consumers that they numbers are LHV, not HHV.

Beware of pellet stove companies such as Enviro that claim to have "EPA tested efficiency" numbers on their website.  These numbers are likely to be exaggerated ones and would be much lower if they were actually tested to EPA specifications by a third party lab.

Pellet stoves have much wider variability in efficiency than cat or non-cat wood stoves, and some consumers are inadvertently buying models that are under 60% or even 50% efficient despite higher claims by manufactures.

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

  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.