Pellet stove performance makes big gains as interest in renewable energy grows

In 2009, the average pellet stove emitted 2 grams of smoke (particulate matter) per hour. No one had any idea which stoves were efficient and which weren’t.  Ten years later, the average pellet stove certified to be sold as of May 2020 emits only 1 gram per hour.  By cutting that number in half, the emissions around homes that heat with these new pellet stoves are barely perceptible.  

Efficiency has also risen, with the average efficiency of pellet stoves now nearly 74%, but some as high as 87%, based on the EPA's certified stove database.  Ten years ago, average efficiencies were under 70%. 

A variety of factors led to these performance improvements but it’s not yet clear if they will lead to an uptick in installations.  Based on interviews with numerous pellet stove retailers, most consumers don’t buy pellet stoves based on increased performance values. 

“We see a lot more customers who want a renewable heat source and are not so concerned whether it’s going to save them money or not,” says James Cusano, a veteran stove retailer at the Stove Barn near Concord New Hampshire.  “Consumers are looking for ease of use – which means big hoppers, minimal maintenance and thermostat controls – and many now want to avoid fossil fuels.”

Cusano says heating preferences in New Hampshire are changing and consumers have more options today than they did 10 or 20 years ago.  Heat pumps are an option, but with cold New England winters, stoves are still prized.  For pellet stoves, consumers “want it to be as close as possible to heating with a modern central system, but with a biomass fuel source, and without the much larger investment required for a pellet-based central heating system.”

Other retailers, such as Richard Thomas, who runs Courtland Hardware in Maryland, say renewable energy is not a big driver.  He says many people buying pellet stoves used to have a wood stove and are looking for the ease of use that pellet stoves offer.  Maryland has a stove incentive program driving consumers toward cleaner and more efficient pellet stoves, rather than basic wood stoves.  Massachusetts and New York have similar programs that require turning in an old wood stove.  These states show that harnessing interest in stoves and moving towards pellet heating can be a key strategy for decarbonizing heating fuel loads. 

The renewable energy movement so far is benefiting heat pumps far more than pellet stoves, though both offer the potential for low carbon space heating. Until there is a lot more renewable electricity on state grids, advocates say pellet heat should be an obvious choice, helping to avoid winter electric peak demands that are more likely to be met with combined cycle gas plants than with renewables.

National pellet stove trends

Pellet stoves are well-known in the wood heating community, but many consumers and renewable energy experts still don’t know exactly what they are and how they differ from wood stoves.  No precise figure exists about the number of pellet stoves in use today, but most experts think it is more than 1 million.

Current sales figures are not public but past figures show large swings between years amidst a long term growth pattern.  Pellet stoves have never outsold wood stoves, but they have come close, selling up to 150,000 units some years.  More recently, pellet stoves may be only a quarter or third of wood stove sales (in the 50,000 per year range). Even at 50,000 units a year, however, pellet stoves are being installed at a scale that merits more attention.

There is evidence that pellet stoves are gaining traction, partly from demand of people who used to heat with wood and partly from first time buyers.  In Vermont, one of the few states that includes pellet stoves in surveys on home heating devices, more than 8% of homes use pellet stoves or boilers as their primary heat and an additional 3.6% use pellets as a secondary heat source.    This is a rapid rise from 2008 when less than 2% of homes used pellets as a primary fuel.

Source: Vermont Residential Fuel Assessment, 2014 - 2015

Maryland does not track pellet stove installations but the state released data showing that 85% of people receiving rebates for an efficient stove chose the pellet stove rebate over the wood stove rebate.  Richard Thomas sells pellet and wood stoves at three locations in Maryland in northeast Maryland and he says that 90% of the stoves he sells are pellet and less than 10% are wood stoves.  

The best pellet stoves consistently emit well under 1 gram of PM per hour, 1/5^th or 1/10^th the emissions of a  wood stove in the hands of the average consumer who may rarely get the results achieved in the test lab.  Like many modern combustion engines – from cars to furnaces – modern pellet stove emissions are almost always invisible and undetectable by the nose, but pellet heaters  still emit more per hour than a car and much more than a modern gas or oil furnace. Bigger PM reductions are still underway with pellet combustion technology and one pellet stove model was recently tested at 0.22 grams an hour, a level that some thought was nearly impossible.  

One stumbling block for pellet stoves is the public perception that they accelerate deforestation.  There are large volumes of sawdust and scrap wood from lumber yards that have been used to make heating pellets in the northeast for decades.  Those volumes can rise or shrink depending on the strength of the housing market and the economy overall.  There was little confusion about the source of fiber for pellets until large corporations started harvesting whole trees from the southern US to ship to Europe to make electricity.  It is now commonplace for people to think that’s how heating pellets are made.  Likewise, many don’t distinguish between small scale heating at 75% efficiency and industrial scale electricity production at 25% efficiency.

The large percentage of pellet stoves sold today is great news for air quality agencies since they operate far cleaner in homes than wood stoves. It’s also great news for the renewable energy community since a pellet stove can run 24/7 and is usually a home’s primary heat source. A pellet stove used as a primary heater in most parts of the US will typically make as much energy as a 5kW residential solar panel installation.

Prices

Accurate price data is not available to track changes between 2009 and 2019.  At the high end, top brands like those from Harman, Quadrafire and Travis sell for $3,000 - $4,250 and installation can add $500 - $750 or more.  At the low end, there is still an abundance of very affordable pellet stoves.  At least seven manufacturers make pellet stoves that sell for $1,000 or less (two of them appear to be on the market illegally and are not EPA certified.) 

A top value stove, the PelPro, has several models that sell for about $1,200 and are among the cleanest and most efficient on the market.  Scott Williamson, a professional pellet stove repair technician from Massachusetts, says with their large hoppers and solid reliability history, it’s hard to find a better pellet stove for anywhere near that price point.  PelPro stoves are sold by big box stores, requiring consumers to find and hire a professional installer and repair technicians on their own, compared to specialty hearth dealers who provide those services and rely on the additional income streams.

The number of certified pellet stove models nearly tripled from 56 in 2009 to 171 in 2020.  Most pellet stove models in 2009 were not yet certified, due to a perceived exemption which was only supposed to apply to stoves that had an excess of 35 parts air to 1 part fuel.

Data shows that cleaner stoves are more efficient stoves

In addition to becoming cleaner and more efficient, there is now a clearer relationship between cleanliness and efficiency.  About half of the sixty-two 2020 certified pellet stoves are below 1 gram an hour, and half are between 1 and 2 grams.  The stoves under 1 gram had an average efficiency of 75.9% and those above 1 gram had an average efficiency of 71.7%: a nearly 10% difference.  This provides an additional motivation for consumers to look more closely at the cleanest stoves, as they also tend to be the ones that will use the least fuel for the same heating output.  

Source: EPA Wood Stove Database (room heaters)

James Cusano of the Stove Barn in New Hampshire also found that “the lower particulate emissions seem to require slightly less of the intensive cleaning that the higher emission models do, and that is critical to the long-term efficiency and reliability of any pellet burning appliance.”

In addition, there is a clear correlation between PM and carbon monoxide (CO).  Stoves emitting less than 1 gram of PM had an average of 0.18 pounds of CO per hour.  Stoves with more than 1 gram of PM per minute emitted an average of 0.29, 38% more.  CO is one indication of good combustion and is expected to correlate with PM.

The road to better performing pellet stoves

The year 2015 marked the biggest turning point for pellet stoves because the EPA required all pellet stoves to be certified and report the results of efficiency tests.  Stove retailer James Cusano says he has seen bigger changes in the bottom of the market than at the top.  Going forward, “the middle and top market models will continue to improve their automations, while the bottom will focus on continuing to try to meet the new minimum expectations at budget price points,” Cusano said.

The EPA decided to set the same PM regulatory levels for wood and pellet stoves, giving pellet stoves a very easy target.  The average pellet stove certified to the 2020 standard of 2 grams an hour emits about 1 gram an hour.  The federal IRS tax credit has also used a single efficiency number for both wood and pellet stoves, which would make far more pellet stove models eligible for a tax credit, if it were to be re-enacted.  Bills in the House and Senate supported by AGH, HPBA and scores of other groups propose a tax credit with a 75% efficiency limit as of 2020 would make most pellet, catalytic and hybrid stoves eligible and most non-cat wood stoves ineligible. However, after this tax credit was passed in December 2019, manufacturers began undermining it by certifiying that stoves even in the low 60s qualified for the tax credit.  HPBA declined to comment on how efficiency should be calculated even though efficiencies have always been averaged, just like automobiles average highway and city miles to get a final number.

Innovation and competition have also played an important role in the trend toward cleaner and more efficient pellet stoves.  A half a dozen models now emit less than a half a gram of PM per hour and a dozen are over 80% efficient.  

The US Energy Information Agency releases annual forecasts of heating fuels each fall but do not separate pellet from wood heating.  This year they predict a slight national decline in primary wood heating to a little less than 2% of US households (about 2 million homes), down from 2.2% about 5 years ago.  However, about 8% of American homes use wood or pellets as a secondary heat source, according to the EIA’s recent Winter Fuel Outlook.

Per capita use of wood and pellets as a primary residential heating fuel.  Two states – Vermont and Maine – are in the 10% - 25% category, sharply reducing fossil heating fuel demand in that region.  Source: EIA 2019 Winter Fuel Outlook

Continued improvements in pellet stove performance will help the technology serve a core population of people who currently heat with expensive oil, propane or electric resistance heaters, as well as those looking for renewable options.  And, it may not be long before pellet stoves are designed and tested at or below 0.1 gram an hour, a technological milestone that could coincide with state and national policies aimed at increasing renewable heating goals.

EPA releases long-awaited searchable wood heater database

A screen shot of part of the
navigation of different fuel types
in the new EPA database

Consumer friendly site is cause of worry for some

Updated Dec. 2020  - The EPA released its long-awaited searchable stove and central heater database, overhauling a decades-old practice of using basic excel sheet lists.  The database is now a very user friendly site for consumers and all stakeholders.  A simple search that could have taken hours, now takes seconds.

The EPA said the new database was designed to“improve accessibility and usefulness” by allowing users to search for the cleanest stoves, the most efficient stoves, those designed to burn cordwood and other attributes.

A wide range of stakeholders, from industry to states to non-profits, had been urging the EPA to switch to a modern searchable format for nearly a decade. The painfully slow development of the database at times seemed to epitomize the government's reputation to move at a snail’s pace. The list is maintained by the EPA’s Office of Enforcement, which like much of the EPA has been hit with repeated budget cuts and loss of staff in recent years.

The sleek new functionality of the list, allowing users to focus on one parameter or another, is also worrying to many in the stove industry. Traditionally, this list of certified wood heaters has not been a primary information source for consumers. But with this new functionality, consumers may start relying on it more and more, leading to some unintended results, such as worse buying decisions or ones that favor some manufacturers over others.  Similar to the feature in the old excel spreadsheets, the new database now also indicates new additions.

One fear is that consumers will put too much reliance on higher BTU output if they can easily search and cross reference by these values. Right-sizing a stove is already problematic, and the BTU values on the list are overinflated due to loose parameters that allow labs to show high BTU output. Another fear, expressed by some manufacturers at the recent HPBA Expo in Nashville, is that consumers will favor “Cord Wood” stoves over “Crib Wood” stoves because they are not familiar with the lexicon of stove testing and the legacy of crib wood. 

The EPA chose to include a box that helps consumers identify the cleanest and most efficient stoves,

and some say that this puts unwarranted attention to values that won’t necessarily translate from the lab to the home. This “Quick Searches” box will likely be used by consumers who don’t understand pellet stoves work similarly in the home as they do in the lab, but wood stoves can only achieve the optimal lab numbers with a large bed of coals, dry wood and careful operation.

This “certified fuel type” feature also sheds light on one the biggest problems with the new searchable data – accuracy. Six wood stoves were initially listed as using wood chips as a fuel, an apparent mistake according to one of the manufacturers of those stoves. As of November 2020, two stoves are still listed as being tested with wood chips, even though no such test method exists. This could hurt sales of those units if consumers are relying on the database to narrow down the stoves they may purchase. EPA staff are quick to say that this is a work in progress and it is incumbent on manufacturers to vet the list and provide the EPA with corrections. In 2017, the HPBA warned the EPA that many inaccuracies existed in the database. Many of the same errors are still listed two years later.  A whole new frontier of recognizing deficiencies is now being opened up by an Alaska initiative that is reviewing all certification documents.

The Alliance for Green Heat welcomes the new database and had the opportunity to provide input on several occasions as other stakeholders did. Some of our suggestions and wording was adopted and some was not. AGH believes that the new database will help consumers become more educated about the working of stoves and the terminology, but it will take time and effort by the wood heating community.  AGH is currently urging the EPA to add a column showing what test method was used to identify single burn rate stoves and stoves that used an alternative test method.

The release of the database was coordinated with the update of some key pages on the EPA's Burn Wise website. The EPA finally changed their page on hydronic heaters which previously defined and pictured them just as outdoor boilers, a change that AGH had urged them to make for years. They also made major changes to their efficiency page which had not been updated since the EPA began requiring testing and reporting of efficiency of stoves.

Features and functions

·      Pellet stoves

The database shows 98 out of the 242 models are pellet stoves.  Nearly half of the  pellet stove models are 1 gram or under.

·      Catalytic Stoves

The database shows that 30 of the 144 models are catalytic, and another 19 are hybrids which also use catalysts. 

·      Hybrid Stoves

Wood stoves are divided into three
subtypes - cat, non-cat and hybrid.

Hybrid stoves, which almost all use both catalysts and air tubes for secondary combustion, are listed as a subtype and  there are now 19 stoves listed as hybrid. AGH is urging the EPA to also add “automated stoves” as a subtype in the future. Both hybrid and automated stoves offer great promise to help consumers run stoves more cleanly.

·     Cord vs. Crib wood
                  As of Nov. 2020, 83 of the 144 wood stoves were tested with cord wood, indicating a surging popularity with the ASTM test method, that allows more flexibility in the lab.

      BTU Output

With tighter homes and a new breed of tiny homes, it is now easy to search for stoves with the lowest BTU output. Many models are tested at less than 25,000 BTU. AGH believes that many units still have erroneously high BTU values based on loose parameters in lab testing and reporting, and these values should be used with great caution. 

Firebox volume

The cubic size of the firebox is an equally useful tool to estimate BTU output.  They range from 0.5 to 4.4 cubic feet. AGH has concerns that some BTU output figures are exaggerated due to the allowable calculations that labs can use to estimate heat output.  Small fire boxes are usually considered to be up to 1.5 cubic feet and good for holding a fire for no more than 4-6 hours.  Medium fireboxes are in the 1.5 to 2.5 range and usually can hold heat for 6 - 9 hours and large fireboxes are 2.5 - 4.5 cubic feet and can easily hold heat overnight.

Test method

In December of 2020 the EPA added a column to designate the test method that was used to determine emissions, but they have not yet populated the column with any data. This will help better understand which are single rate burn stoves, for example, and which stoves got variances.  The detail will be too technical for the average consumer but useful for stove geeks and agencies.

·      Efficiency

The EPA has chosen to use the term “overall efficiency” instead of simply “efficiency.” Some manufactures use “optimal efficiency” or “maximum efficiency” instead of publishing the EPA tested efficiency, which is lower. One hundred out of 244 models tested at 75% HHV efficiency or greater.

·      Carbon monoxide

Like efficiency, carbon monoxide is required to be tested and publicly disclosed, but there is no regulated minimum or maximum that must be met.  The CO listing raised concern from some who worry that consumers may use it instead of PM as a primary indicator of cleanliness, or that consumers may think it’s an indication of amounts of CO emitted into the room.

· 

·       Previously certified

The database also shows the 205 stoves that were previously EPA certified at 4.6 grams or higher, a feature that could be very helpful for change out program managers who want to target older certified stoves, many of which need replacement.

·      Key terms and definitions

The EPA provides a new page with definitions of key terms such as adjustable burn rate vs. single burn rate heaters, fireplace insert, wood pellets, etc.

·      Central Heaters

The database is separated into two: “Room Heaters” and “Central Heaters” and you have to select one or the other or your search may turn up empty. There are 32 central heaters with 12 that use pellet fuel.  Of the 32 heaters, only 3 are forced air furnaces.

·
Not included in the new database

Some stakeholders have urged the EPA to include more search attributes, such as the test method, lab, and a link to the detailed lab report that manufacturers are required to post on their websites. The list also does not say whether PFI certified pellets were used during certification testing and are thus technically required to be used by the consumer.  Up until 2007, the list used to include the deadline that the five year certification certificate expired.  Up until the summer of 2015, the list included the outmoded estimated default efficiencies, which listed all non-cats at 63%, cats at 72% and pellet stoves at 78%.  The default efficiencies were set based on testing in the mid and late 1980s, resulting in relative accurate estimates for wood stoves, but helping to develop the enduring myth that pellet stoves had such high average efficiencies.

Contact Rafael Sanchez at the EPA's Office of Enforcement to address errors or omissions in the database, (sanchez.rafael@epa.gov) at (202) 564-7028.

Non-cats cleaner than catalytic or pellet stoves in new certifications

In the most recent updated list of EPA certified stoves, 17 more units became 2020 compliant, meeting the 2020 EPA regulations of emitting no more than 2 grams an hour.  While it is not a large sample size, among this batch of newly certified units,  the non-catalytic stoves averaged 1.2 grams an hour, whereas catalytic stove averaged 1.3 and pellet stoves averaged 1.4.  It is not yet clear if the non-catalytic stove designers used new innovative technology or just fine-tuned existing strategies to reduce particulate matter.

Of the 17 newly certified stoves,
non-catalytic models are the cleanest

Many industry experts have argued that the 2020 emission standard of 2 grams an hour favors catalytic and pellet stoves.  But we are seeing some non-cats come in below 1 gram an hour, including 2 of the 5 in this recently certified batch.  Many of the 2020 compliant non-cats do fall in the 1.5 to 2 gram range.  And every once in a while, a stove goes into the lab and doesn't quite meet the 2.0 gram standard, like a IHP stove that recently came out certified at 2.1 grams.  Assuming this unit was not tested with cordwood (which are allowed up to 2.5 grams per hour), this means that the model can only remain on the market in the US for less than 18 months until May 2020, unless the EPA were to approve a sell-through.

Efficiency

The average efficiencies show a less surprising trend: the 13 newly certified non-catalytic and pellet stoves had the same average efficiency – 69%.  The four catalytic stoves, including one hybrid, had an average of 77% efficiency.  These efficiency numbers are typical of averages of all stoves on the market. Pellet stoves have long had the reputation of being a more efficient technology, but over the last several years, as manufacturers were required to disclose efficiencies,  we saw that pellet stoves had a far greater range on the low and high end, with the average being about the same as non-cats.  Even among this small sample, pellet stoves had the lowest efficiency unit (at 60%) made by Sherwood Industries.  Sherwood also made the highest efficiency pellet stove in this newly certified batch – at 77%.

Efficiency could be a more important metric if Congress re-instates the tax credit for residential wood heaters.  That credit was worth $300 but expired in December 2017.  Stoves needed to be 75% efficient to qualify for the tax credit, but manufacturers were allowed to claim eligibility without disclosing their real efficiency, allowing virtually all stoves to qualify.  The practice of exaggerating efficiencies and misleading consumers got to the point that even the industry association, the Hearth Patio & Barbecue Association, changed course in 2018 and recommended that only publicly disclosed efficiencies on the EPA list of stoves be used in the future to determine eligibility.  If the credit is reinstated, there is a chance that the eligibility number could be reduced to 73%, in part to help more non-catalytic stoves qualify.

Carbon monoxide

The other metric that test labs are now required to report is carbon monoxide, another very important test of cleanliness, along with particulate matter.  By far the cleanest technology in terms of CO is the pellet stove. The pellet stoves in this small batch had an average of 0.42. grams an hour of CO, the catalytic had 0.63 grams and non-catalytic stoves had 1.2 grams – almost double the CO of non-cats and triple that of pellet stoves.

A stove's ability to burn off carbon monoxide often tracks its ability to burn off particulate matter.  Of the pellet stoves, the three with the lowest CO also had a lower average PM (1.2 grams an hour), and the three with higher CO had a higher average PM (1.5 grams an hour).  

Overall progress towards 2020

There are 533 stove models on the latest list of EPA certified stoves that are currently in production.  Many of those units will never be changed to become 2020 compliant and many are already not being produced any more.  Industry experts say that the number of stove models will contract as we get closer to 2020, likely in the range of 300 – 400 models.  As of February 2019, 119 models are 2020 compliant.  (The number of 2020 compliant models is consistently under-reported due to delays in processing and notification.)  Many manufacturers may also have completed their R&D and/or their testing but have not submitted the data to the EPA. 

Most stove manufacturers have at least a third to half of their models 2020 certified – including larger brands such as American Energy Systems, Blaze King, Even Temp, Fireplace Products International, Hearthstone, Pacific Energy, Rais, Ravelli, RSF/ICC, Sherwood Industries, Stuv, Travis and Woodstock Soapstone.

However, the two largest value stove manufacturers in the US market – US Stove and Englander – only have pellet stoves certified and still do not have any 2020 compliant wood stoves.   They sell to big box stores, which buy even earlier than specialty retailers.  It is still too early to tell if big box stores will replace Englander and US Stove models with models from other manufacturers, likely at higher prices.  Some in industry hope that the 2020 emission standards will help specialty heath stores regain some of the market share they had lost to the big box stores over the past decade.  

Tiny homes, tiny wood stoves: photos, ideas and designs

Updated: Nov. 2020 - With the advent of the tiny home movement, there is a rise in interest in tiny stoves to heat them.  Tiny stoves have always been around, mainly driven by the sailboat industry, but also for yurts and small homes.  Small stoves are often thought of as stoves with a firebox of less than one cubic foot.  But some are much smaller than that and may put out no more than 10,000 BTUs.  There will also likely be a growing market for very small pellet stoves, like the Thelin Gnome, as living spaces get smaller and tighter. 

The paradox of heating a small space is that it may not be hard to heat up, but it also gets cold quickly after the stove goes out.  The fireboxes are so small that they cannot hold much fuel.  Often, tiny stoves need to be reloaded every 20 - 60 minutes, depending on the size of the fuel and whether the stove is just getting going or has a decent coal bed.

A few of these stoves are EPA certified, including the Kimberly and Katydid and the Gnome pellet stove.  (But the Kimberly and Katydid will not be certified after May 15, 2020 when EPA standards get stricter.) And the EPA has slowly begun to add firebox size their searchable database, and 69 out of 207 stoves that are 2020 certified have firebox sizes.  The smallest, at half a cubic foot is made by the Danish manufacturer Moreso. If they are designed for boats, vans, trailers or for camping or other non-residential spaces, they should fall outside the EPA's regulations, which only pertain to residential heating. But it is unclear whether they should be certified if they are used as a residential heater.    See our other photo essays on wood stoves styles around the world, wood fired hot tubs and firewood gathering around the world.

To minimize space, tiny stoves can be mounted on the wall. Using wood stoves in boats, vans and tiny homes can pose a great risk of carbon monoxide build up than in larger spaces. Be sure to install a CO detector, store your ashes outside and ensure the draft doesn't reverse back down the chimney.

Tiny stoves are often installed on counters or shelves so that operating and cooking on them is easier.

Yurts are traditionally heated with larger, inefficient stoves, not small, sleek ones like this.  

The 1991 Cape George 36,  "Privateer", is outfitted with the "Little Cod" marine wood stove

112 square foot mobile tiny home, heated by tiny wood stove

Minimalist living inside Mt. Brown Hut, New Zealand

Antique Refurbished Box Stoves

Inside a traditional style "Sheep Wagon" in Idaho

Stove featured in a custom "tiny" house 

This Van found on Vancouver Island, BC spotlights a small stove and split wood

Living low-key in Anchorage, Alaska, this mobile home is outfitted with The Kimberly Stove

"Halibut" by Navigator Stove Works

The "Sardine" wood-burning stove measuring in at 12"x12" doubles as a cook stove 

Swiss man with a wood stove in his 1990 Volvo

The "Sardine" by Navigator Stove Works, seen aboard W. Atkin "Ingrid" in Washington State

The Gnome pellet stove is the smallest pellet stove on the market and claims to run for more than 24 hours on one hopper load of pellets at low heat.

The Viking 30 cookstove is part of a retro line of wood stoves from Sweden.

A small stove in a classic Airstream trailer.

Thanks for reading!  Check out our photo essay on wood stoves from around the world and sign up for our free monthly newsletter here for more ideas on how to heat with wood, pellets, etc.

Enviro redesigns EF2 pellet stove, raises efficiency 19%

Improved heat transfer led to major
improvement in efficiency without
any price increase of the EF2.

When the EPA began posting actual efficiencies on its list of certified stoves, all of sudden consumers could see which brands of pellet stoves were saving them more money in fuel costs and which weren’t. A popular pellet stove, the EF2, made by a prominent brand, Enviro, turned up at the very bottom of the list at 58% efficient, surprising many. The company had been advertising the stove at 87% to consumers.

Enviro appears to have redesigned the stove in an effort to avoid the distinction of having the least efficient stove on the EPA list. In July of 2016, Enviro tested their new version, the EF2-1, only a year after testing the older version, and it came in at 77%, nearly 20% higher than the old version. Now, due to greater scrutiny, they also advertise to consumers that the stove gets 77% efficiency. At the same time they lowered the emissions from 1.8 grams an hour to 1.4 grams an hour. Their carbon monoxide values also went from 25 grams an hour to 7 grams an hour, a dramatic improvement.

At 77% efficient, the new Enviro EF2-1 is one of the most efficient pellet stoves made by a major North American stove company. The average pellet stove is likely to be around 70% efficient, but this may rise as companies like Enviro compete to design higher efficiency stoves. One of Harman’s lower efficiency stoves, the Advance, tested at 67% efficiency. That stove is being discontinued, which could be partially due to its low efficiency. (Harman still claims that the stove is eligible for the federal tax credit for stoves that are 75% efficient or greater.)

The US Stove model 5660 is now one of the least efficient pellet stoves on the market at 62%, but the company still says that it is eligible for the 75% federal tax credit. St Croix makes two pellet stoves, the Hastings and Ashby, that each tested at 66% efficiency by EPA-approved test labs. However, the company website claims that the Hastings is 83% efficient and that its “efficiency ratings are verified by an independent lab.” The Hastings owners manual confirms that the independent lab rated the stove at 66% efficiency.  The tax credit is set to expire on Dec. 31, 2016.

The Enviro EF2-1 is also sold by Hudson River Stove Works under the brand names Chatham, Davenport and Kinderhook.  Despite the lab test showing the stoves are 77% efficient, Hudson River Stove Works continues to tell consumers that they are 85% efficient.  Unlike the manufacturers of automobiles and major appliances, there is nothing stopping wood and pellet stove manufacturers – or their retailers – from blatantly misleading consumers, as Hudson River Stove Works does.

The EPA has made efforts to bring more transparency by requiring manufacturers to post the test lab documents on their websites. These documents show additional details about the stove, including its carbon monoxide levels and emissions results at each burn rate. Enviro is one of the companies that complies with this rule and posts this information so that consumers can see testing information about the EF2-1 here.

In the November update to the EPA list of certified stoves, the EPA added a column for carbon monoxide, as all stoves tested after May 2015 have to test for and report their carbon monoxide emissions levels along with their particulate matter emissions and efficiency. However, the EPA has only input the CO test results for eight stoves as of December 14, 2016.  The EF2-1 at 7.4 grams of CO per hour has the lowest.  The five non-cat stoves with CO values range from 87 to 186.