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 urges manufacturers to stick to May 2020 compliance deadline; says its working towards a cordwood test method rulemaking

On October 15 the EPA provided an update on its wood heater website page urging “affected entities to continue efforts to certify compliance with the NSPS in light of the upcoming May 15, 2020, compliance date.” According to NSPS legal experts, the EPA sometimes issues such updates to provide more transparency when stakeholders need certainty due to an approaching deadline.  

[March 11, 2020 update: The EPA finalized amendments to the 2015 NSPS and did not provide a retailer sell-through.  They did remove pellet fuel minimum requirements but retained the list of prohibited fuels in the 2015 NSPS.]

The October 2019 update is widely interpreted to mean that there will be no sell-through for whole house heaters or any other significant changes in the regulations issued by the EPA in 2015. However, the details of any changes to the 2015 rules will come later this fall when the EPA issues the Final Rule.  

The news was welcomed by the Alliance for Green Heat and many stakeholders, including manufacturers and importers of wood heaters who have invested in R&D and retesting of their heaters that comply with May 2020 emission standards.   Nearly 200 models of wood and pellet heaters are certified to the 2020 standards and virtually all stove companies say they will be ready for May 2020.  Some include innovative designs that achieved emission levels that are six times cleaner than the maximum allowed in 2020.

The sectors of the wood heater industry that most needed a sell-through are the outdoor wood boiler and indoor forced-air furnace makers, both of whom are represented by the trade group Hearth, Patio and Barbecue Association (HPBA).  HPBA’s strategy of seeking relief from Congress and the Administration appear to have fallen through, leaving its litigation against the EPA as the most viable channel for relief.  But that relief will likely not occur before May 2020.

Test methods

 

A Canadian company who never
had an EPA certified heater
saw a new market open up
for their AirBilo Furnace.

Much of the EPA’s update addressed test methods, and the EPA noted that a newly approved broadly applicable alternative test method for furnaces “may facilitate the ability of manufacturers” of furnaces to comply by May 2020.  This is not the type of relief sought by HPBA, and it’s not yet known if many other furnaces will use this test method for certification.  However the EPA puts it in the context of providing some relief.  It was given to a Canadian company mostly known for maple syrup boilers, but who also makes a very affordable forced air furnace.

The EPA used this update to message that it is already moving on to the next proposed rulemaking, which will be on cordwood test methods.  The update said, “in the coming months, the agency is initiating a series of roundtable discussions with states and other stakeholders to inform the agency’s direction toward a cord wood-based compliance test method.”  In March 2016, the EPA laid out a process for developing improved cordwood test methods. By statute, the next NSPS should be in 2023 but the EPA could issue this rule making earlier.  AGH believes the next NSPS should not focus on reducing allowable PM without first modernizing test methods to ensure heaters are designed for real world use.

Part of the HPBA’s litigation focused on an agency decision to set a 2.5 gram an hour emission standard before setting a test method to meet that standard. Subsequently, an industry led ASTM committee developed the E3053 test method which has become a commonly used method along with the standard crib wood method that has been in use since the late 1980s.   The ASTM method is being widely used now but came under scrutiny by the EPA because of lax reporting by labs using the method.

NESCAUM is developing "Integrated
Dute Cycle" protocols based on the
way stoves are used by consumers.

Since the ASTM method became a “broadly acceptable” alternative test method, NESCAUM has dedicated substantial resources on a broad and ambitious effort to develop a range of new test methods for stoves, boilers and furnaces, as well as for pellet heaters.  The NESCAUM effort is partially funded by NYSERDA and the process and data is not fully public but ultimately it could provide the largest database of cordwood testing ever compiled to develop a North American test method.  Since test methods need to be data driven, this process may give these NESCAUM protocols an entry point and will challenge others to develop or make public data that can lead to a better protocol.

DOE awards $3 million for R&D to wood stove manufacturers

The MF Fire leadership team in 2018
- Taylor Myers, Paul LaPorte and
Ryan Fisher.

The U.S. Department of Energy (DOE) selected only two companies – MF Fire and ISB Marketing – to receive $3 million for research and development (R&D) through the DOE’s Office of Energy Efficiency and Renewable Energy. The DOE had $5 million for stove and boiler manufacturers but decided to only award $3 million this year.

The two manufacturers are working on next-generation controls and designs for wood stoves that have barely entered the marketplace. Both companies are focusing their efforts on how to make stoves cleaner in the hands of consumers – not just in the test lab – which has become widely recognized as the Achilles heel for the millions of Americans who heat with cord wood.

[Dec. 15, 2019 update - The DOE announced their intention to grant another $5 million for biomass heater R&D in 2020.]

MF Fire received two grants, one for a device that continuously monitors performance of key combustion indicators and delivers real-time user guidance, and the other for a “swirl stove” that induces and maintains swirling combustion and introduces a new balance of primary, secondary, and dilutive air. ISB Marketing, working with its sister company, Stove Builder International (SBI), is developing a Machine Learning algorithm for a self-regulating wood stove that would have a PM emissions rate below 1.2g/h and offer an overall efficiency of more than 75% (HHV).

The SBI team that produced the award
winning prototype of an affordable,
automated stove

DOE is expected to be able to offer R&D grant funding again in 2020 and may be able to stimulate R&D in more wood heater manufacturers. “We applaud Congressional appropriators and the DOE for funding this R&D that can help millions of Americans affordably heat their homes with next generation wood and pellet stoves,” said John Ackerly, President of the Alliance for Green Heat.

The $2 million for MF Fire is a large cash infusion for a young, small manufacturer with lots of innovative ideas and priority on R&D. “This will enable us to hire new people to ramp up our testing and apply techniques and technologies used by other industries," said Ryan Fisher, COO of Baltimore based MF Fire. “For example, eliminating PM by more thoroughly and aggressively mixing fuel and air has not been done by stove manufacturers. Square, rectangular corners create dead spots that inhibit combustion." Mr. Fisher said. Fisher and his original partner Taylor Myers got their start in designing stoves as graduate students preparing for the first Wood Stove Design Challenge in 2013. The rookies won multiple awards before the age of 25 and still haven’t turned 30. Some see them as the face of a new wave of stove designers.

ISB Marketing, with their SBI counterparts, are taking a similar tack but its potentially applicable on a range of stove models from a major manufacturer. ISB is working with Machine Learning algorithm that will learn how each specific user heats his/her stove. The stove will then adjust its combustion parameters to compensate for any “bad” human behavior that tends to increase particulate matter (PM) emissions and reduce efficiency. A home-designed real-time PM monitoring system will be developed to obtain a better understanding of the stove’s behavior.

Mark Shmorhun, the program
manager at DOE who managed
the grant process, at the 2018
Wood Stove Design Challenge

Marc-Antoine Cantin, President of SBI said in an interview that moving innovative and more risky stove projects through a corporation takes longer, as models that have conventional technology are often green-lighted first. “External R&D funding can help reduce risk,” Cantin said. Even with a million dollars from the DOE, a batch of 26 of the new stoves is not expected to be beta-tested until the winter of 2022-23. SBI won second place at the 2018 Wood Stove Design Challenge for designing a simple, affordable stove that allowed the operator to select high or low heat output and used a low-cost control board and thermocouple sensors to ensure that the stove burned cleanly.

The DOE does not disclose how many applications they received or from whom, but it is widely believed that the agency received few applications for the available $5 million pot of funding. John Crouch, Director of Public Affairs for HPBA, said in an interview, “The funding announcement came at a bad year because manufacturers were scrambling to certify their stoves to the stricter 2020 EPA standards. We hope there will be more applicants if the DOE offers the grants next year.”

The DOE also does not disclose who was on their panel of expert reviewers. According to some companies who applied, some didn’t make it through the process because they had not fully completed the application. Others made it through the first round, and then had to respond to specific questions from the reviewers. Ryan Fisher of MF Fire said he got multiple questions about whether his small company could execute two grants and they had a solid plan in place to manage that. SBI got many questions about their corporate structure. They are owned by US-based Empire Group, who also owns ISB Marketing. They plan to carry out R&D for the grant in the US. Other applicants who made it through the first round, didn't make it through the second round.

The one-page summaries of the 3 grants can be found here: MF Fire-Swirl Stove, MF Fire-Performance Monitoring, ISB Marketing-Automated Stove.

This recent entry of the DOE’s Bioenergy Technologies Department which focuses mainly on biofuels, fills a significant gap for the US government. The EPA provides baseline emission and testing standards and the USDA’s Forest Service provides support for larger commercial use of biomass for heating applications. This marks the first time that a US government agency has provided support for companies to push the boundaries of emission and efficiency controls for residential wood and pellet heaters. The United States has the toughest emission standards for residential heaters in the world, which has kept US companies at the forefront of an industry that can provide affordable, low carbon heating solutions in the switch from fossil fuels to renewables.

The original DOE funding opportunity was directed at stove R&D that included:

• Novel and innovative residential wood heater designs to improve combustion chamber geometry, combustion air flow distribution, mixing of combustion air with gasification products, stove baffling designs, etc.
• Improvements in automation of stoves to optimize combustion control.
• Wood heater power generation via thermoelectric module integration
• Improvements in catalyst technologies for emissions reduction