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 66 stoves from 20 companies who post the verified efficiency of at least one of their stoves.
Among the 66 stoves with actual efficiencies, catalytic stoves are the most efficient, averaging 79% efficient. Next comes non-catalytic stoves, that average 72% efficient. And last, comes pellet stoves, at 71% efficient. Pellet stoves also have the greatest range, from 58 to 79 efficiency, a 26% difference.
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.
The EPA dropped the estimated 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. Click here to download the list of 66 EPA certified stoves that disclose their actual efficiency, as tested by B415.1-10, using higher heating value (HHV).
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 EPA has just started to require stoves to be tested for efficiency. Stoves that were tested and certified before May 15, 2015 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 lower than the could be.
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. Some Travis stoves are now approved to display this hangtag.
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.
Wood Stoves with Verified Efficiencies
The non-catalytic stoves on this list range from 65 - 76% efficiency and the catalytic and cat/hybrid stoves range from 75 - 84% efficiency. Pellet stoves range from 58 to 79%.
|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.
Pellet Stove with Verified Efficiencies
As of July 2015, there are seven pellet stove companies with a verified efficiency on the EPA list. Ningboa, a Chinese manufacturer 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 next highest is England's Stove Works 25-SSPO1 at 79% efficiency. The Illinois based company, Seraph Industries, was the first pellet stove company to disclose their actual efficiency, and has a verified 78% HHV efficiency. The average efficiency of US made pellet stoves is probably about 70% HHV, based on several third party studies, but many popular pellet stoves are between 55 - 65% efficient. The Enviro EF2 is listed by the EPA at only 58% efficiency, though Enviro's website claims that the stove 87% efficiency.
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