Friday, January 31, 2014

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

Updated on July 15, 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 40 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.

Three companies provide the efficiencies of all of their stoves to consumers: Blaze King, Kuma Stoves and Seraph.  The Alliance for Green Heat commends those companies for their transparency.  In addition, Kuma now holds the distinction of having the highest rated efficiency of any stove, at 84%, which is generally regarded as the highest that any wood or pellet stove can go. Travis and Pacific Energy deserve recognition as well for showing leadership in voluntarily disclosing their verified stove efficiencies.  Both those companies now have 5 stoves with verified efficiencies.

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 40 stoves that have actual efficiency numbers are likely to be amongst the highest efficiency stoves on the market and are being listed because the companies are proud of their efficiency levels.  The average non-catalytic wood stove is about 70% efficient and the average catalytic stove is probably around 77%.  Higher efficiency stoves save you time and money.

The EPA has never required stoves to be tested for efficiency but will start doing so in May 2015 when their new residential wood heater regulations are final.  Once that occurs, consumers will start to have access to more and more actual efficiency numbers. But some manufacturers may not disclose their efficiencies until closer to 2020, if the EPA allows that, as existing stoves may be grandfathered and not required to retest for many years.

How important are efficiency listings?

Tested efficiencies of wood stoves give an indication of how efficient the stove is when it is operated with seasoned wood.  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 much 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 64 - 75% efficiency and the catalytic and cat/hybrid stoves range from 75 - 84% efficiency. These are all HHV numbers and substantially above the 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.
Of all the wood stove companies that list third-party, verified efficiencies on the EPA list, Blaze King, Kuma and Seraph are the only companies that lists verified efficiencies for all their stoves.

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, has at least one stove which is likely its cleanest and most efficient, and the hangtag in the showroom shows their tested efficiency, at around 83%, instead of the default efficiency. This is their Encore FlexBurn 2400, a hybrid that uses a catalyst and non-cat secondary combustion.

A Step Backward by the EPA

While allowing companies to list actual efficiencies, instead of just default estimated efficiencies was a step forward by the EPA, the EPA is now not requiring that companies provide retail hang-tags on their stoves.  The new regulations will require that all stoves be tested for actual efficiency but now the EPA is only maintaining that data on a pdf on its website, and is not making it easily available to consumers on the showroom floor.   While the efficiency of more stoves should be available after May 15, 2015 on the EPA website, the Alliance for Green Heat believes it is vital for consumers to have this information in retail stores where consumers buy stoves.  The industry trade association, the Hearth, Patio & Barbecue Association, supports the EPA move to stop requiring hang tags on the showroom floor, as does Hearth & Home Technologies, the largest producer of wood and pellet stoves in America. Hearth & Home Technologies does not list the efficiency of any of its stoves.  For more info on hang-tags.

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.

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.

Recommendations for Consumers

For now, the safest thing for consumers who want higher efficiency pellet stoves is to buy stoves that are EPA certified or are made in Europe. A wide range of value and high-end pellet stoves are EPA certified from manufacturers such as Harman, US Stove, Englander,  Lennox and Seraph.  EPA certified stoves tend to be more efficient because uncertified ones can have excess air in the combustion chamber that can drastically reduce efficiency.

The average efficiency of a catalytic stove on the EPA list is 80% HHV, compared to 72% HHV for a non-catalytic stove. The average pellet stove is believed to be only around 68 - 70% HHV efficient. The average particulate emissions for a stove on the EPA list is 1.6 grams per hour for a cat and 3.3 grams per hour for a non-cat. Lower grams of particulates per hour can mean higher efficiency, but there is not always a direct correlation.

The Alliance for Green Heat commends these manufacturers for submitting verified HHV efficiency numbers to the EPA so consumers have access to reliable efficiency information. The Alliance urges consumers to consider purchasing stoves from manufacturers who are transparent and provide verified efficiency information to the public.

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?