Monday, January 7, 2013

Beware of Ads for 99% Efficient Wood Boilers

Alliance for Green Heat, January 7, 2013 - Each issue of Mother Earth News, a magazine that caters to
the granola, Birkenstock and organic vegetable crowd, also carries many ads from outdoor and indoor biomass boiler companies. Actually, we love the magazine, but it carries some very misleading advertisements about wood boilers and furnaces.

The Alliance for Green Heat has regularly put the spotlight on outlandish claims by various manufacturers. This month we feature Kuuma who is advertising "99.4% comb. efficiency" wood burning furnace.   The December/January issue of the magazine also has an half-page ad from Central Boiler stating that their E-Classic "requires up to 70% less wood than other wood-burning appliances."

Exaggerated efficiency claims have become almost commonplace in the boiler and stove industry, taking advantage of consumers who don't know that there is no commonly accepted way to advertise efficiency any more. One rule of thumb: Beware of any appliance claiming 99% efficiency. Any claim of efficiency in the upper 90s is likely combustion efficiency, not thermal efficiency - the amount of useful heat produced by the unit.  Combustion efficiency has no bearing on the useful heat a unit generates which is why stoves, boilers and furnaces manufacturers typically advertise thermal efficiency.  The most efficient wood stove, using EPA approved efficiency standard is 82%, and the most efficient boilers using that same standard are probably under 90%.

Even though Kuuma has been advertising "99.4% comb. efficiency," they deserve credit for posting their third party lab results on their website, which very few manufacturers do.  For consumers who want to read the fine print, which you should if you are going to buy a furnace, these reports are extremely helpful, if you know how to read them.

We at the Alliance for Green Heat applaud Mother Earth News for consistently good editorial coverage of wood heating, partially thanks to their contributing editor John Gulland, and we understand that they aren't responsible for claims made by advertisers. (We also love granola, organic vegetables, home-baked bread, etc. Birkenstock - not so much.)

Update: See the comments section below for a response from a Kuuma representative.  Kuuma has slightly changed their ad to say "combustion" instead of "comb." which consumers may think means combined efficiency.   We urge Kuuma to advertise their thermal efficiency like other manufacturers.  See here for a boiler company that advertised 97% efficiency at the end of a period when EPA had mistakenly endorsed overly high efficiency numbers for boilers.  They stopped using that ad.

Update: In March, 2014, the EPA updated verified efficiencies for outdoor boilers, and has been requesting boiler manufacturers to desist from using misleading information.  


  1. you got somethin' against Birkenstocks?

  2. On our website it states 99.4% combustion efficiency (not combined efficiency) which we achieved on one of the tests we had one for efficiency and emissions with Intertek. This is a fact and the signed PDF is located on our website at We will make MotherEarth print a retraction sorry about the confusion but they must have taken it off our website and messed up words.

    Lamppa MFG Inc.

  3. It could not be more clear that the need for a universal standard which is derived from real world performance is critically needed for bio mass burning equipment. Consumers are looking for accurate information that will depict what the can actually expect from these appliances. The industry does them and itself by publishing "best case" numbers or numbers which tell only a partial truth.

  4. For those who understand combustion and heat exchange efficiency, the high number of combustion efficiency means there is virtually no creosote. The wood is basically totally consumed, leaving only fine ash, and no unburned fuel condenced in the chimney (creosote). This is a very good thing and no smoke is the result.

  5. We get a lot of people including competitors who snide at combustion efficiency and don't fully understand how impressive over 99% is when you burn wood.
    As was stated above on 1/28 basically the whole piece of wood is consumed and no unburned fuel (creosote) will remain.
    It does make us upset that we were used as an incorrect example when we have never falsely advertised anything... Assumptions shouldn't be made especially when it can hurt a companies image. I didn't have all the information when we initially responded. For space reasons when advertising we abbreviated combustion as comb. and didn't even think twice about it.

  6. This subject of "efficiency" is especially interesting when it comes to qualified OWBs. Method 28 OWHH was the process for certification but it was found lacking so modifications were made to improve it. I assume you're aware that it's is now called Method 28 WHH. Supposedly, the changes better reflect thermal efficiencies, too. It appears that the LHV was also increased to 7938 BTU/LB.

    What I don't understand is if Method 28 WHH is the standard for certification why are some manufacturers using European EN303-5 to qualify for the tax credit? Is it because there are only two burn categories and the LHV is lower by 200 BTU/LB when using this standard compared to Method 28 WHH?

    Additionally, I still can't wrap my mind around how EN303-5 reflects real world efficiencies. Correct me if I'm wrong but it's my understanding when conducting the test using 303-5 the OWB never goes into close damper mode. As we all know this is completely outside the norm as to how these devices are operated in the real world. Many consumers purchase OWB's oversized and consequently the unit ends up in close damper mode a large percentage of the time. If I'm correct then achieving 75 percent outside the lab would be difficult unless the device is accurately matched to the square footage of the building calling for heat and only dry wood is used. Obviously, if the unit is matched correctly and the fire continuously burns then time between loads is reduced causing more cold trips to reload, something a lot of folks don't like doing.

    Also, I was hoping you could shed some light on the so called gasification process used in qualified OWBs. If the unit is not operated in a continuous burn mode does the gasification of the unit cease? If so, then I assume the PM measurement in the lab is also not accurate compared to use in the field?

    I was hoping you wouldn't mind taking a few minutes to answer some of these confusing questions. Perhaps I'm completely off base here? On a side note I really enjoy reading your newsletter.

  7. It may be impressive that your boiler achieves a high combustion efficiency but this does not translate to thermal efficiency. By using combustion efficiency in ads it implies you're taking advantage of consumers ignorance on the subject. As you are aware, the thermal efficiencies that were posted on the EPA's Burn Wise website were removed because Method 28 OWHH did not accurately measure thermal efficiency. Has your company retested under the revised Method 28 WHH? If so, would you be willing to post the complete test results for the models you sell?

  8. Both of our furnaces were tested in 2010 to -CAN/CSA B415.1-10 “Performance Testing of Solid-Fuel-Burning Heating Appliances”- We are a small company and the testing process was very expensive so we won't be testing again until the new regulations are finalized. I don't see why we wouldn't post the results again, because we are very confident in our indoor furnaces.

  9. I do apologize for confusing your stove with hydronic heaters. I am not familiar with the test standards associated with forced air system but I do stand by my comment about the differences between combustion and thermal efficiencies.

  10. Thank you... It's kind of funny because we are the only company that I'm aware of that actually posted a signed PDF of the entire testing process for everyone to view. So for anyone to think that we would actually be trying to intentionally deceive anyone is pretty ridiculous. :)