Six tips to buy the right pellet stove

Retailers say BTU output can be most confusing issue

Glenn Robinson is one
of many retailers struggling
to help consumers avoid
relying on manufacturer
claims about BTU output.

Updated on Jan, 7, 2021 - Glenn Robinson has been selling and installing pellet, wood and coal stoves in Pennsylvania for 11 years, and one of the biggest problems he faces is sizing the stove.  “I became tired of false information from manufacturers about how many BTUs they claimed their stoves put out” he said in a recent interview.  “Customers see these exaggerated BTU numbers from a small stove and think it will heat their home, but it won’t.  The result is that the stove is undersized and there is premature wear and tear.  One model from a big name brand would only last for 3 – 4 months before needing repair or even full replacement,” he said.

Glenn is not alone in identifying exaggerated BTU listings as one of the biggest problems consumers face in buying a stove.  Scott Williamson, a Massachusetts pellet installation and repair technician says that he sees stoves “all the time that are being run on high 24/7 and pellet stoves just aren’t designed to do that.”  Both installers say that under sizing of pellet stoves is one of the biggest problems, and urge customers to consider larger (higher BTU output) stoves if they live in average size homes in the northern half of the country and plan to use the stove a lot.

Buying a pellet stove can be a confusing process for consumers (but as of 2021 high efficiency pellet stoves and installation costs are eligible for a 26% federal tax credit!)  Retailers are likely to push the brands they sell and manufacturer websites don’t tell the whole story.  Objective, third party reviews are rare and often outdated.  Consumer Reports did a pretty good review in 2009 but used very limited criteria and didn’t test for durability.  The Alliance for Green Heat (AGH) also undertook third party testing in 2015 and issued a detailed online report on some issues including BTU output, maintenance and efficiency. (Like Consumer Reports, AGH conducted completely independent testing by purchasing all the units and doing all of our own testing.)

This blog identifies and discusses six rules for consumers to keep in mind when buying a pellet stove, with a focus on sizing.  This is not an exhaustive list but it’s a good place to start: 1. Don’t undersize, 2. Beware of cheaper stoves, 3. Look for range of heat output, 4. Understand maintenance requirements of the stove, 5. Look for cleaner stoves and 6. Beware of stoves with no efficiency on the EPA list

AGH tested six popular pellet stoves.
Almost all performed well during
intensive 30 day testing, but did not
live up to some manufacturer claims.

Pellet stoves can be a very effective and affordable way to provide primary or secondary heat for your home without the smoke that wood stoves often create in the hands of the typical user. Wood stoves require lots of work on the fuel side of the equation, but pellet stoves involve more work on the appliance side of the equation. 

The Alliance for Green Heat also monitors advertising of pellet stoves and has found over the years that the great majority of companies vastly overrate the amount of heat their stoves put out.  The EPA list of certified wood and pellet stoves is not perfect but it remains the best source of BTU output for consumers. 

Most EPA-certified pellet stoves are listed as producing a maximum of 25,000 – 40,000 Btu and minimum of 7,000 – 13,000 Btu. The average pellet stove on the EPA list, according to data provided by third party test labs, put out a maximum of approximately 31,800 Btu and a minimum of approximately 10,050 Btu. 

The stove with the highest maximum Btu on the EPA list is the Harman P68 at 53,500 Btu (advertised at 71,200 Btu input).  When a stove manufacturer lists Btu input, it refers to amount of Btus in the fuel, if you were to get 100% of those Btus into the room.  But the average pellet stove is around 73% efficiency, which means you will get 73% of the fuel’s potential heat into the room.  (This is similar to the AFUE – the annual fuel utilization efficiency – that is used on gas and oil boilers and furnaces.)

The stove with the lowest maximum Btu is the Thelin Gnome pellet stove that puts out up to 9,000 Btus.  However the company advertises three times that - 27,000 Btus - without any explanation.  Manufacturers usually exaggerate Btu, thinking that it will make their stoves more attractive, but in the case of the Thelin Gnome, there are people looking for stoves to heat very small places and the exaggerated Btu output may make them think even the Gnome is too big.

Here are six critical things for consumers to keep in mind when purchasing a pellet stove:

1.       1. Don’t undersize. If the stove is going to be your primary heat source you will likely need a medium or large pellet stove, even if a smaller unit advertises high BTU output.  Ignore BTU numbers on manufacturers websites and literature and check the EPA list.  The maximum output for pellet stoves is in the 30,000 – 50,000 range, enough to heat all or most of a small or medium house in most climates. “Don’t plan to run the stove all the time at its highest setting,” warns Scott Williamson “or you will be calling someone like me to fix it quicker than you think.”  When we tested six popular pellet stove models, we calculated an output of no more than 21,000 BTUs, far below what the EPA listed and even farther below what manufacturers claimed.

It is possible to oversize the stove and that can be a problem, but is not nearly as common as under sizing.  “For example, the Harman P68 is notorious for being installed in small areas like mobile homes but they gunk up when they aren't allowed to get up to temperature for a bit before they shutdown,” says Scott Williamson.

2.      2. Beware of cheaper stoves. There are some good budget wood stoves on the market, but with pellet stoves, you are more likely to get what you pay for than with wood stoves.  “If you want a reliable stove that puts out a lot of heat, we urge customers to ignore pellet stoves under $2,500,” says Glenn Robinson.  Scott Williamson generally agrees but has seen some basic stoves like the Pel Pro in particular holds up very well.

3.      3. Check for range of heat output.  Most stoves can put out about 3.5 times more heat at their highest setting, compared to their lowest.  Some stoves have a tiny range, putting out only 1.5 times more heat at their highest setting.  If you live in a more moderate climate, in the early fall and late spring, you may want just a little heat, and still have the capacity for much greater heat output on the coldest days and nights of winter.  All other things being equal in a stove, you may want a stove with a larger range of heat output and you can check the range of all stoves on the EPA list of certified stoves. In our tests, we found that the Enviro M55 insert ran continuously for an impressive 49 hours on its lowest setting with a tested hopper size of 60 pounds and it ran for 22 hours on its higher setting.  However, with a 37-pound hopper, the Englander 25 PDVC only rain for 15 hours on its lower setting and 13 hours on its highest setting, indicating a very low turn down ratio.

4.       4. Understand maintenance requirements. If you don’t clean your stove regularly and have it professionally serviced once a year, don’t expect high BTU output.  Most consumers get subpar performance from stoves and have to repair them more often because they are not maintaining their stoves according to the owner’s manual.  Pellet stoves are not like wood stoves: they have lots of moving parts and need cleaning of the burn pot and inside the stove on weekly, and depending on the stove, a daily basis.  Pellet stoves that are not cleaned regularly can lose 10% or more of their efficiency – and their heat output, and lead to costlier repairs. Understand the daily, weekly and annual maintenance requirements from the start and don’t put them off.  When we tested six popular pellet stoves, we found that the three more expensive ones (Harman, Quadra-Fire and Enviro) could go for a week or more without cleaning the burn pot.  However, the Englander, Ravelli and Piazzetta needed daily burn pot cleanings.

5.       5. Look for cleaner pellet stoves and ones that are 2020 certified.  Pellet stoves are far cleaner than wood stoves, even if they both have the same particulate matter in grams per hour.  Particulate matter is the tiny stuff that smoke is made out of and pellet stoves should not have any visible smoke after the 3-minute start up.   The average pellet stove used to put out about 2 grams of particulate per hour.  But since the new EPA regulations took effect in 2015, pellet stoves have become even cleaner and more efficient.  As of April 2020, more than half of the 2020 certified pellets stoves emit 1 gram or less per hour. This makes pellet stoves more suitable in more densely populated suburban and even urban areas.  Choosing a cleaner pellet stove means a cleaner flue pipe and cleaner air around your and your neighbors’ homes. You can now easily search for the cleanest pellet stoves on the EPA's new searchable database.

6.       6. Beware of efficiency numbers on manufacturer and retailers websites.  As with BTUs, manufacturers routinely exaggerate the efficiency of their stoves on their websites, so if efficiency and saving money is important to you, check the EPA list of stoves for efficiency ratings.  Until May 2020, many companies still hadn't even reported their efficiency to the EPA, but thanks to new regulations, all companies have to test for and disclose their efficiency.  Pellet stoves range from 58 to 87% efficiency, so do your homework and check the EPA list.  As of Jan. 1, 2021, consumers can get a 26% tax credit when buying and installing pellet stoves that are 75% efficient or higher. Click here for more details.

Do not rely on Manufacturers Certificates that claim their stoves are eligible for a federal tax credit without first checking the efficiency on the EPA's searchable database of certified heaters.  Even large companies that make good quality stoves like Jotul and QuadraFire have claimed that stoves as low as 66% efficiency are eligible for the tax credit.  The credit is supposed to be for stoves over 75% efficiency.  

The EPA used to allow companies to calculate efficiency based on a default of 78% efficiency, even though most pellet stoves are below that, explains Ben Myren, who runs one of the stove test labs approved by the EPA. The result is a 5-10% exaggeration of some stoves on the EPA site, something that the EPA has not publicly acknowledged. (Some incentive and change out programs - Maryland, Massachusetts and New York - require that the stove have an efficiency listed on the EPA list to get the full rebate.)

Appreciating these six factors are likely to help you make a better decision, but we also encourage consumers to rely on feedback from friends, neighbors and others who own pellet stoves. One site that can be helpful for research is hearth.com.  

A final note of caution is to take advertised hopper size with a grain of salt.  Most manufacturers also exaggerate hopper size.  Of the six models we tested, Harman and Ravelli exaggerated their hopper size by 15 – 18%, while Enviro didn’t exaggerate at all.  Choosing a stove with an advertised hopper size of 50 – 60 pounds can be a good idea, as it means the hopper will likely hold 45 – 55 pounds and you can empty an entire 40 pound bag in it when its low.

Could a Thermoelectric Wood Stove Pay for Itself?

By Ken Adler, AGH Senior Technical Advisor

Payback calculations are common in the residential solar photovoltaic industry where homeowners want to know how long it will take for them to recoup their initial investment. If you purchase panels outright, payback periods depend on a variety of factors including a utility’s price for electricity, tax incentives, and amount of daily sunlight hours. A range of 5 to 8 years is possible however, it can be as wide as 3 to 15 years.[1]

Answering the payback question for thermoelectric wood stoves is one of the objectives for the 2018 Wood Stove Design Challenge. In the meantime, there are several ways to begin answering this question with information already available. It is also useful to look at how use of a thermoelectric wood stove in combination with another energy-saving system, i.e., solar, could prove beneficial to the homeowner and thus both industries as well. For example, in northern states and Canada, a thermoelectric wood stove could reduce the number of residential panels needed and thereby save the homeowner thousands of dollars in panel costs.

Early Thoughts on Payback

The retail price of a thermoelectric module is around $57.50 for a 22-watt module, or $2.61 per watt.[2] One critical point to make here is that the power output of our 22-watt module assumes an optimal hot-side temperature of 300 C (572 F) and cool-side temperature of 30 C (86 F). This ideal temperature differential is very difficult to achieve in real world conditions, so the real-world cost per watt for thermoelectric modules will be higher. However, cost should decrease and efficiency improve with widespread adoption of thermoelectric modules, similar to what happened in the solar industry. For example, DOE estimated that the installed cost of a solar panel declined from $7.06 per watt in 2009 to $2.93 in 2016, a reduction of 60 percent.[3] If we go back to 1977, the cost of a solar panel was $77 per watt. It is not unreasonable to expect a decline for the cost of thermoelectric modules as economies of scale reduce production costs.

Of course, when a thermoelectric module is placed into a wood stove there are other associated costs. The primary cost by far is the heat exchange system. As I’ve discussed in a previous post, to generate at least 100 watts of power, it’s likely that a water-cooled heat exchange will be needed. The current retail price for a 100-watt water cooled thermoelectric generator, which includes eight thermoelectric modules, is $599, or $5.99 per watt. One question the competition will attempt to answer is how much this heat exchange will cost when it is integrated into the design of the wood stove.

Secondary cost considerations include the price of the wood stove, its installation, and fuel costs. The price for a larger size 50,000 BTU wood stove can range from $900 to over $4000, and the average consumer spends about $2,500. Since a thermoelectric wood stove would be providing both heat and electricity, it is difficult to separate out how much of the cost of the stove is for each function. The more crucial point for now is that many larger size stoves, which can generate up to 50,000 BTUs and meet the 2020 EPA NSPS standard, are available for as little as $1,300. While this does not include the cost of installation, it does suggest that the wood stove portion of the costs should not be a major obstacle.

The cost of installing a thermoelectric wood stove into a home should not necessarily be that much greater than the cost of installing a traditional wood stove. One additional cost will be attaching the power outputs from the thermoelectric wood stove to an inverter. However, if we assume that early adopters will already have or are planning to get a solar PV system (more on this below) the cost of the inverter would not be a major obstacle.

Finally, one can assume that the fuel cost for a thermoelectric wood stove is essentially zero because the wood stove is already being used to heat the home. A thermoelectric module will convert only 3 to 6 percent of the heat from a woodstove into electricity, while the remaining 94 to 97 percent passes through the module and is released as heat into the home. In other words, the module is only using a very small percentage of the heat generated by the stove to produce electricity.

Value in Combining Technologies

While more in-depth analysis is needed, it’s possible that a thermoelectric wood stove could help reduce the size and cost of solar PV systems in northern climates that have limited sunlight/solar radiation in winter. For example, a typical 5000 watt solar PV system in Vermont produces 6,280 kWh of electricity per year, while the same system produces 7,913 kWh in Los Angeles.[4] Most of this difference is due to the low winter time output in Vermont between October and February: For example, the Vermont system produces 239 kWh in December, as compared to the Los Angeles system’s 473 kWh. If the Vermont resident wanted to generate the same amount of power as in Los Angeles, they would need to increase the size of their solar PV system from 5000 watts to approximately 6300 watts. At the current cost of approximately $3.36[5] per watt installed for residential solar, this could cost the Vermont resident an additional $4,368 for additional solar panels.

Alternatively, instead of purchasing extra solar panels, the Vermont resident could invest in a thermoelectric wood stove to boost their winter time power output. As we mentioned in our previous blog, a wood stove with a 150 to 200-watt thermoelectric generator operating 16 - 20 hours per day could generate 93 to 124kWh of electricity per month, which would be a good boost to the Vermont output of 239 kWh in December. And, at 0.16 $/kWh for electricity in Vermont, the thermoelectric wood stove could save the homeowner an additional $15 to $20 per month.

While a real payback calculation for a thermoelectric wood stove will need to wait until prototypes go through more testing and we get results from the 2018 Wood Stove Design Challenge, the available information suggests thermoelectric wood stoves could help reduce the cost of residential solar installations, and potentially save homeowners thousands of dollars.


[1] http://solar-power-now.com/the-typical-solar-panel-payback-period/
[2] See our Resources page for a list of thermoelectric retailers.
[3] NREL. U.S. Solar Photovoltaic System Cost Benchmark. September 2016. In 1977, solar panels cost $77 per watt.
[4] NREL PVWatts Calculator
[5] EnergySage. Solar Marketplace Intel Report. April 2017.

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All wood and pellet furnaces must be certified by May 15, 2017

One of the loopholes in the new EPA regulations about to close

The cleanest and most efficient
forced air furnace is the Maine
Energy System Auto Pellet Air.
It delivers 89% efficiency.

One of the big loopholes in the new EPA wood and pellet heater regulations is closing this month.  Small forced air furnaces were required to meet new emission regulations in May 2016, but many very small furnaces declared themselves to be large furnaces, giving them until May 2017 to meet the new standards.  As of May 16, 2016, all forced air furnaces, large and small, must emit no more than 0.93 lbs per mmBTU of heat output regardless of whether they are wood or pellet units.

In April 2017, there were six certified forced air furnaces, four of which use wood and two of which use pellets.  The average emissions rate ranges between 0.06 to 0.84 lbs, with the average at 0.411 lbs, less than half the current standard.  However, as of 2020, this class of heaters must meet a far stricter standard of 0.15 lbs/mmBTU.  (This is the subject of litigation by the HPBA.)  Only one of the current six models, the Maine Energy System Auto Pellet Air,  emits less than 0.15 lbs, but it has to be retested using a different test method to comply with the 2020 standards.

Of the six on the market in April 2017, there is an efficiency range, from 48% to 89%.  Both ends of the spectrum are listed as pellet heaters.  At the top end is the Maine Energy System’s Auto Pellet Air, which was developed by OkoFEN, a leading pellet boiler company in Austria.  At the bottom end is US Stove’s 8500 multi-fuel furnace.  (US Stove also has a certified cordwood furnace that has lower emissions and higher efficiency than this pellet model.)  The average efficiency of the six

The US Stove 8500 pellet
furnace was the least efficient
certified furnace at 48%. Now, US Stove
has a 33% efficient log wood furnace. 

furnaces is 66%.

(June 2017 update: There are now 10 certified furnaces on the market, with an average of 60% efficiency and a huge range stretching from 33% to 89%.)

At the end of May 2017, it will be clear how which forced air furnaces did not get certified.  There are many more coal furnaces on the market today, compared with 3 or 4 years ago, as some companies have added grates and other slight modifications to outdoor wood boilers and furnaces in order to keep them on the market as coal units.  Coal heaters are still not covered by EPA emission regulations, so renaming a wood boiler or furnace a coal boiler or furnace is still a loophole used by some companies.

Review of wood pellets for BTU, moisture and ash content

The Internet is full of opinions and reviews of wood pellet brands.  However, data of actual properties of various wood pellet brands is hard to locate.  It cost under $100 for a lab to test ash, moisture and BTU content of a pellet. We tested 4 popular brands, along with corn kernels, to see the variability between brands.  Our overall conclusion: much less variability than we expected (except for the corn).

Click on the brand name to see the full lab report from Twin Ports Testing for American Wood Fibers, Pennington, Curran Renewable Energy, Nation’s Choice , and Takoma Park Silo corn.

Conventional wisdom is that you should buy a couple bags of pellets to see how they work on your stove before buying a ton or more.  That's good advice, as some stoves handle a much wider range of pellets, while others do not.  It’s especially good advice in light of the lab testing we did, that shows little variation between moisture, ash and BTU content of four popular brands.  

The four brands we bought – made by American Wood Fiber, Curran, Pennington’s, and Nation’s Choice – are all major brands but only represent a small fraction of available brands.  Two of them are PFI certified, which means that they must meet certain quality guarantees and cannot have more than 1.0% ash, 8.0% moisture, and 0.5% fines, among various other requirements.  All four brands of pellets we tested fell within the parameters required by PFI premium grade, for the criteria that we tested – ash and moisture.  We did not test for fines or for durability or bulk density or chlorides – things that can be important for performance.  The cost for testing those qualities is about $250, more than we wanted to spend for each test.

We highly recommend choosing a brand that is PFI certified as it ensures a basic level of quality that should not be taken for granted.  A few manufactures add discarded wood pallets into their fiber mix and while some old pallets may still have clean wood in them, many do not.

Pellet manufacturers, whether they are PFI certified or not, usually do not disclose actual BTU, ash or fines, but just say that they do not exceed a certain level. 

Ash content: Ash is one of the biggest concerns of consumers since high ash pellets can clog up some stoves and require more cleaning.  Of the four brands we tested, the ash content was relatively similar, ranging from about 0.3% to 0.6%, far below the acceptable level under the PFI certified standard of 1.0%.  

BTUs: 

Whether your stove is 60% efficient or 80% efficient, you will get more heat from a pellet with more BTUs.  Some pellet brands may have up to 8,800 BTUs per pound and some only 8,000. The highest BTU pellets are made from 100% softwood, like Douglas Fir and will have lower ash and will cost more. That is only a 9% difference in BTU output.  The higher BTU pellets we tested had 8,439 BTUs per pound, 5% more than the lowest BTU brand, which had 8,011.  Softwood pellets may also burn cleaner.  

Moisture content:

Moisture content varied even less than ash and BTU content between the four brands we tested. The low was 5.1% and the high was 5.8%.  PFI allows up to 8%.

Look for the PFI certified
box to help ensure you
are buying high quality
pellets.

Price:

Price on all these 4 brands can vary depending on the time of year, the location, the seller, and whether or not a ton is purchased. Pennington’s, Nation’s Choice, and Curran have all been available at big box outlets in the $250/ton range over the past several months.  The American Wood Fiber Ultra Premium White Pine is more expensive, as 100% softwood pellets tend to be, especially on the east coast.

Options for future testing

Testing and publishing the BTU, moisture and ash content of dozens of common wood pellet brands would be a great resource for consumers.  Please let us know if you agree or have suggestions about how to develop and maintain a reliable, independent data base of pellet characteristics.

This report and the pellet testing was supported in part by a grant from the Maryland-based Rouse Charitable Foundation.