Thursday, October 24, 2019

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, 1/5th or 1/10th 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.


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.

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