IRS proposes using EPA database to verify 75% efficiency for tax credit

Industry is split three ways on question of eligibility.

July 2025 update: Congress revoked the wood heater tax credit as of Dec. 31 2025, ending what was meant to be a 10 year extension under President Biden. Expenses are eligible for stove purchases and installation of stoves prior to Dec, 31. 

Nov. 2024 - The IRS issued a proposed rule on October 25 to give guidance on how manufacturers can interpret“75% efficiency.” They are proposing to adopt the EPA database as the means of determining efficiency, which has been long expected by many in industry. 

The proposed rule is long-awaited by many who grew frustrated over the years that the IRS could not do what many felt was obvious: recognize the EPA efficiency listing. AGH was a prominent advocate for a uniform way to list efficiency as a way of protecting consumers, making a level playing field for manufacturers and instilling more faith in the industry. AGH often publicized exaggerated and misleading efficiency claims over the years.

Comments to this IRS notice are due by December 24, 2024 and a hearing is scheduled for January 21, 2025. The IRS notice can be found here.

Congress stipulated that biomass heaters at 75% efficiency, using the higher heating value, were eligible for a 30% tax credit, up to $2,000. However, Congress revoked that as of Dec. 31, 2025.

Most manufacturers were already using the efficiency numbers on the EPA database as the arbiter of which stoves or boilers were 75% efficient or higher. The EPA number is an average of the efficiencies on all the certification tests. But a few manufacturers chose to say their stoves qualified for the tax credit if any of the certification tests were 75% or higher.

The third faction, made up of masonry stove manufacturers, urged the IRS not to issue any further guidance, so that they could claim masonry stoves at 75% or higher could qualify even though they are not listed on the EPA database because they are not required to be EPA certified.

According to the Congressional Research Service, approximately 48,300 taxpayers claimed the biomass tax credit in 2023, making it the least likely tax credit that taxpayers claimed other than for home energy audits. There is no public data on how many biomass stoves and boilers were sold in recent years, but experts say that an average of 200,000 is plausible. EPA has the data but it is not organized or compiled.

Currently 67% of the 101 certified pellet stoves are 75% or higher, based on the EPA database figures and 45% of wood stoves are. However, 92% of cat and hybrid stoves are 75% or higher and only 15% of the 106 non-cat stoves on the market are 75% or higher.

The legacy of using efficiency to qualify for this tax credit, that started in 2008, raises many questions. Arguably, cleanliness is more important than efficiency when using wood, a renewable fuel that a substantial percent of Americans cut or collect on their own instead of purchasing it. The result is that stove manufacturers now focus more on efficiency, while sacrificing R&D to achieve incremental reductions of particulate matter. Congress controls the efficiency number, while EPA sets emissions levels, and a lower efficiency threshold could allow the EPA more leeway to set stricter emissions standards.

Most manufacturers did not submit comments on the proposed regulations. All comments can be found here. Among stove manufacturers, some manufacturers who make lower efficiency stoves (e.g. US Stoves) argued for the stricter definition of efficiency, while those making higher efficiency stoves (Hearth & Home Technologies) argued for a more lenient definition.

The comments by stakeholders outside the wood and pellet heating community provide an interesting snapshot into views on incentives for wood and pellet stoves and boilers. For instance, the American Lung Association does not support biomass stoves or boilers should be qualified energy property regardless of efficiency rating. The California Air Resources Board (CARB) and the Attorney Generals of MA, CO, DE, IL, ME, MD, MI, NJ, NY OR, RI and DC believe a full carbon lifecycle analysis should be done to better calculate an efficiency rating.

However, based on their comment and the sources in the footnotes, it appears that they are confusing biomass to electricity, rather than focusing on biomass heat. While this is a common mistake in the media, it is notable that whoever drafted this comment for these states also made it. Nevertheless, these states do not oppose the tax credit but argue that a stricter one could be better. No commentator suggested that only pellet heaters, that are consistently cleaner and more efficient, should receive the tax credit. A carbon life cycle analysis however, would most likely favor cordwood over pellets.

Support using EPA database

Alliance for Green Heat: The most reliable method to protect consumers, ensure that tax credits are
going to compliant models and create a level playing field for manufacturers is for Treasury/IRS to specify that eligibility is limited to units listed in the EPA Certified Wood Stove Database that have an overall weighted average efficiency of 75% or more using the higher heating value of the fuel. (AGH’s full comment can be found here.)

BPA, ACEEE, ASE: The most reliable method to protect consumers and to ensure that tax credits are going to compliant models is for Treasury/IRS to specify that eligibility is limited to units listed in the EPA Certified Wood Stove Database as having an overall efficiency of 75% or more using the higher heating value of fuel.

Blaze King: Our company has always viewed the overall efficiency to be the metric intended by the IRS as the qualifier for the 75% high heating value.

Travis: In the interest of efficiency and the preservation of resources, the IRS should rely on EPA’s database to confirm whether biomass stoves meet the 75 percent rating requirement.

US Stove Company: Therefore, for a biomass stove or boiler regulated by the EPA to qualify for the 25C credit, only the average “overall efficiency” is reported in the EPA Certification report should be recognized. In addition, this same efficiency number will be posted on the EPA Wood Heater Database, therefore easily verifiable. This will eliminate any question or “gaming” of the tax credit.

Support using any single test run

Hearth & Home Technologies: In our view, the Treasury Department and the IRS should issue guidance stating that biomass stoves meet the definition of "qualified energy property'' provided they have a "a thermal efficiency rating of at least 75 percent (measured by the higher heating value of the fuel as reflected in a single certified test run)." Providing this guidance will resolve the current uncertainty about how to meet the HHV requirement. By establishing the single test criteria, a greater number of biomass stoves could qualify for the tax credit, thereby giving consumers more affordable choices to replace noncertified heaters while burning an efficient renewable energy source.

Stove Builder International: Manufacturers should be able to qualify a property …provided this efficiency number is 75% or greater and can be found in the property’s test report. An efficiency number of 75% or greater should be obtained when the property is used at a combustion setting typically used by consumers. For instance, in the case of a wood stove, the products are typically used by consumers at the low setting. That is, consumers use their stoves in slow-combustion mode to get an “overnight burn”. The stove can be used at a higher setting, but this setting is normally recommended upon start-up only. The basis of their argument is that manufacturers will “make up any number they want.” This could not be farther from the truth. We don’t know where this paranoia comes from.

If the efficiency criteria do not offer enough flexibility and most non-catalytic wood stoves cannot qualify for the 25C tax credit, we feel that the IRS misses its objective of helping the middle class to switch to cleaner, more efficient biomass appliances.

Support current language without further guidance

Masonry Heater Association: the IRS not to issue guidance that conflates the regulations of different types of biomass heaters, potentially imposing the requirements of one category of biomass heater onto another category, for tax credit eligibility. For example, woodstoves must be on the EPA's certified list, EPA Wood Stove Database, to be legally installed; however, this is not a legal requirement of all categories of biomass heaters, e.g. masonry heaters. Masonry heaters are a category of biomass heating appliance that the EPA has chosen to defer regulating.

Tulikivi: we feel that guidance is not needed as the original text is clear enough and allows masonry heaters that meet the efficiency requirement to qualify for the tax credit despite not being on the EPA list of certified appliances

Support strict enforcement based on efficiency tiers

Comments Of The Attorneys General Of Massachusetts, Colorado, Delaware, Illinois, Maine, Maryland, Michigan, New Jersey, New York, Oregon, Rhode Island, And The District Of Columbia; The California Air Resources Board; And The Ramsey County, Minnesota, Attorney: With respect to Section 25C’s biomass provisions, we urge Treasury and the IRS to strictly enforce energy efficiency tiers to verify qualification for biomass stoves and boilers. Per British thermal unit (BTU), wood has about the same carbon content as coal, and, according to EPA, wood contains about 75% more CO2 per BTU than natural gas. As a result, wood that is harvested and burned for energy immediately increases greenhouse gas emissions—even where it is displacing fossil fuels. Biomass combustion also emits other harmful air pollutants, like particulate matter, which is connected to a multitude of adverse health consequences including premature death, cardiovascular effects, asthma, bronchitis, pneumonia, chronic obstructive pulmonary disease. To avoid inadvertently increasing greenhouse gas and other harmful pollutant emissions through biomass incentives, Treasury and the IRS should comprehensively evaluate lifecycle greenhouse gas emissions in calculating the efficiency rating of eligible biomass. If, however, Treasury and the IRS elect to rely on EPA wood stove certifications to demonstrate efficiency ratings, they should not allow certification based on test methods 125 and 127 (relying on ASTM 3053), which allow too much variability and manufacturer and laboratory manipulation.

Do not support including biomass heaters in the 25C tax credit

American Lung Association: The ALA recognizes that pollution from the combustion of wood and other biomass sources poses a significant threat to human health and supports measures to transition away from using these products for heat production. As such, we do not believe biomass stoves or boilers should be considered as part of a qualified energy property regardless of efficiency rating.

Other comments

Governor’s Office of NJ: Biomass stoves and boilers are a concern. It’s likely we would have difficulty supporting incentives for biomass but there may be cases that make sense.

Rewiring America: Treasury should structure the updated Form 5695 such that each product category (heat pumps for space heating/cooling, heat pump water heaters, biomass stoves, and biomass boilers) has its own line and can be tracked accordingly. This is crucial to track how many claims are filed for heat pumps and heat pump water heaters; otherwise, it would be impossible to distinguish between claims filed for heat pumps and biomass products.

Tall wood stoves: an elegant tradition lives on, mostly in Europe

Tall stoves evolved in Europe partly because smaller homes and apartments had little space. Tall stoves also offer space for thermal storage, which is also more needed if your wood supply mainly consists of smaller diameter logs. 

Vertical fireboxes are still the norm in Europe but they rarely reach the heights they used to, except as masonry heaters. Today, the vertical European firebox style typically accommodates shorter and smaller pieces of wood, good for a evening fire, but not to hold heat overnight.  

The abundance of cheap wood in America led to less of a priority on thermal storage.  Instead of using less wood, and capturing more of the heat, Americans were able to design stoves that held logs big enough to slowly burn overnight in horizontal burn chambers.  

More vertically oriented stoves were common in America in the 1800 and 1900s in the iconic potbelly stoves, designed as much for coal as for wood.  All sorts of “parlour” stoves also had vertical shapes, designed as heat exchangers so that heat would be transferred to the room before going too quickly up the stack.  The poor man’s heat exchange used to be longer single walled pipe that would snake vertically and then horizontally through a room, often collecting and dripping creosote before exiting the room. 

Visit our other international photo essays on firewood collection and stacking, wood fired hot tubs, tiny stoves for  tiny homes boats & RVs, and typical wood stoves from countries around the world.

The original tall masonry stoves may have emerged in central and Eastern Europe in the 1600s but were rarely this ornate.  These would represent heaters built and used by very wealthy families but the inside design and operation was common in middle class families as well.  See more photos and histories on this site. 

Tiled masonry heaters like this emerged in the 1800s and were common in the 1900s.  They had cast iron and then steel doors, clean out caps, warming ovens and were site built to go as high as they could. 

In the 1960s and 70s, thousands of these hold masonry heaters were destroyed as fossil fuel became cheap and widely available.  And, despite their design to burn hotter and faster than modern steel stoves, as populations increased and cities and towns became larger all over Europe, they began to pose significant pollution problems.

Howell Harris, perhaps the world’s leading historian on wood stoves discusses the demand for very tall stoves, emphasizing their use in non-residential settings, “including "Halls, Nurseries, Nurseries, Churches, Public Offices, Stores, Counting and Green Houses, Work Shops, Steam Boats and Ships' cabins, &c. &c." and also of the shared interest of the inventor and his customers in maximizing heat output and fuel economy.   His site has as much or more detail than anyone could hope for along with scores of high-quality photos.

Many of these elegant, tall stoves, made either of cast iron or tile, were designed for coal, but could also use wood.

While stoves like this are available on the North American market they are almost all imported from Europe and remain far more popular there.

The Victorian Age is reflected in the designs and names of parlor stoves. These stoves simulate the architecture of castles, Gothic churches, and Italian villas. They are also lavish and intricate in design. Made at the height of cast iron technology, such stoves display some of the finest examples of casting known today.  Antiquestoves.com has many more examples. 

The evolution of Danish Morso stove designs from 1854 to 2008. around the turn of the century, when Morsø began to produce and provide tiled stoves and heaters to schools, churches, the railways, ministries and not least to the royal household. This put Morsø seriously on the map, and in 1915 Morsø received the coveted title of Purveyor to the Royal Court. In the 1950’s, the tiled stoves were replaced by central heating, but opened but opened space for wood-burning stoves in which you can see the flames,

Adventures in masonry stove testing from 1988 to 2017

by Norbert Senf, 

Chair of the Masonry Heater Association Technical Committee

Left to right: Mark Champion (in his 
VT test lab), Boris Kukolj (Tulikivi), 

Chris Prior (MHA President), Norbert 

Senf (blog author)  and Jean Francois 

Vachon (soapstone stove builder). 
Photo credit: Mark Seymour.

EPA started regulating wood burning stoves for particulate (PM) emissions in 1988. Regulation was limited to airtight heating stoves. Masonry heaters were not regulated, the stated reason being that they were likely to be clean burning.

In Europe, only carbon monoxide (CO) emissions were regulated. CO is easy to measure, however PM can be very tricky. Wood smoke includes  compounds that will only be captured by a filter if you cool them down and condense them. This is done in the laboratory by mixing them with air in a dilution tunnel, and this is thought to simulate what happens in the ambient air in the real world.

State and county air quality authorities soon started to address wood smoke, and would often pass a generic local regulation that banned all appliances except those that were EPA certified. We, the fledgling Masonry Heater Association (MHA), decided to seek EPA certification.

Although we "knew" that masonry heaters were cleaner even than EPA stoves, nobody had ever measured the PM on one with the dilution tunnel method. With funding help from the Wood Heating Alliance (now HPBA), we were able to participate in a $100,000.00 test method development project for masonry fireplaces and masonry heaters. The project took place at Virginia Polytechnic Institute (VPI) in 1989 and was headed by Dr. Dennis Jaasma.

The results were interesting, with some surprises. EPA did not accept the proposed test method. We immediately realized that we needed do a lot more testing,  and that we would need to develop the capability to do it ourselves.

We were fortunate in being able to arrange for training with OMNI-Test, one of the leading EPA-accredited certification testing laboratories, then and now. OMNI developed a training session for us that took place in September 1996. It included presentations by regulators, an emission chemistry expert (Dr. Jim Houck),  and laboratory testing personnel. Dr. Stockton (Skip) Barnett showed us the low cost portable dilution tunnel that he invented, known as the Condar. He developed it while working for the Condar Company. It was widely used at the time by the major stove manufacturers for in-house testing to develop their certified  stoves.

The attached Powerpoint, Repeatability of Cordwood Combustion Particulate Measurements,  presents a summary of the work we have done at the Masonry Heater Association to calibrate the Condar against the EPA Method 5G laboratory dilution tunnel. It includes a close look at the PM testing repeatability issues,  a major discussion point over the years. We have recently completed 2 cordwood studies, using very carefully matched loads in a masonry heater. Repeatability was within plus or minus 15% - 25%, depending on the ignition method. With crib fueling, we were able to get within 10% repeatability on PM, and within 1.5% repeatability on CO.

Test Results, Presentations and Photos from the 2014 Collaborative Stove Design Workshop

Test Results

Updated on Nov. 24

Part of the Workshop rules was a requirement that teams had to publicly share their test results, which is a key part of the collaborative and educational process. During the Workshop, each team presented their test data to the 50 attendees who had the opportunity to discuss the results and give feedback to the  team.  Unlike EPA test, which starts when the stove is already hot, we used a warm start, capturing some start-up emissions, we used cordwood instead of crib wood and we used higher moisture content wood. Note: any gram per hour (g/h) references in the below test results are not comparable to g/h values from EPA test labs because we did not follow the Method 28 test protocol. 

1. MF Fire, the Mulciber. Powerpoint link.
2. The Kleiss stove. Powerpoint link.
3. Wittus Twinfire, Powerpoint link.
4. The VcV, PDF link.
5. Catalus Ventus, PDF link.

Team Presentations about their Stoves
Each team presented the concepts and technologies in the stoves. For a brief technical overview of all the stoves with contact info for the Teams, click here.

1. The Mulciber (powerpoint)
2. The Wittus Twinfire (pdf)
3. The VcV (pdf)
4. The Catalus Ventus (pdf)
5. Kliess (powerpoint)

Expert Presentations
During the Workshop, there were a series of expert presentations and webinars about automation, traditional stove technology, public health implications, air quality, regulatory issues and other relevant topics.

1. Dr. Tom Butcher, Brookhaven National Lab, Review of the Automated Stove Test Protocol (powerpoint)
2. Webinar with the five teams, hosted by BTEC.
3. Glenn Miller, Fairbanks Air District,  Technology Improvements vs. Behavior Modification (powerpoint)
4. Ellen Burkhard, NYSERDA, Renewable Heat New York (powerpoint)
5. Norbert Senf, MHA, Emission Testing of Masonry Heaters (powerpoint)
6. Gael Ulrich, Smoke Particle Formation Fundamental, (pdf)
7. Peter Cullen, Wohler SM 5000 (powerpoint)
8. Phil Swartzendruber, Puget Sound Wood Stove Retrofit Open Challenge (pdf)

Feedback Survey: Results of a 10 question feedback survey about the Workshop by teams, participants and organizers.

Photos: Day 1

Ivana Sirovica, Jessica Peterson and Jeff Hallowell, from ClearStak Brookhaven National Laboratory.

Rebecca raking coal bed to prepare for the next load of fuel. 

Thanks to John Pilger and Chimney Safety Institute of America and Olympia Chimney for donating pipe and installation!

Indigo Hotel in Riverhead NY - our base for the week

The Testo shows real time emissions, with top line showing particulate matter (PM)

Rebecca Trojanowski removes filters. The dark circle in foreground are the particulates on a filter from the test burn that will be weighed to determine grams per hour.

Even the kindling is carefully weighed so that each stove gets the same warm up rick.

Jessica Peterson from ClearStak working late into the night to prepare for testing tomorrow.

Photos: Day 2

Taylor Myers showing a thermal image of the Mulciber stove. 

Ben Myren, Tom Butcher and Eric Schaeffer firing up the New Zealand VcV stove. 

Lab in Bldg 815 with the VcV and Kleiss stoves.  (They brought 2 of exact same stove in case they needed it.)

Taylor Myers showing a real time digital display, using bluetooth, of temperatures in his stove.

Developed by ClearStak, this real time digital display shows 154 degree stack temperature, 529 in the firebox and 451 in the catalyst. Estimated efficiencies were in the mid-80s. 

Glenn Miller from the Fairbanks Air District on the left, Rob Rizzo from Mass. Dept. of Energy, and Gaetan Piedalue and Marc Suave from Polytest Labs, a EPA accredited test lab. Ellen Burkhard from NYSERDA is peering into the stove. 

Ben Myren, Tom Butcher and Eric Schaeffer firing up the New Zealand VcV stove.

The Wittus Twinfire's downdraft mechanism, where the fire gets sucked into lower chamber and then passes through catalyts before going back up the stack.

Day 3

Corey Van, one of the young ClearStak staff that helped build the Catalus Ventus. 

Rebecca Trojanowski loads the Catalus Ventus.

The new Testo moisture meter that reads moisture without "pinning" the wood.

Norbert inspects the Condar, placed right below the triple walled pipe.

The tube on the right of black pipe is a Condar, which operates very similarly to a dilution tunnel. Norbert Senf is using it concurrently with the Testo PM analyzer.

A warm up test load made by Ben Myren. This top down burn, with smallest kindling on top, and larger kindling on the bottom is a very efficient way to start fires.

Amanda Aldridge of the EPA talks with Norbert Senf (behind flue pipe) about the Condar analyzer. Rob Rizzo from Mass. Dept. of Energy in upper right.

Electronic controllers that can be put in wood heating systems that were part of Jeff Hallowell's presentation. Harold Garobedian in red jacket on right, and Rafael Sanchez from the EPA behind him.

A new Testo moisture meter that works without pins. It can measure moisture at the center of the wood, not on the edge.

George Wei hangs almost upside down to put a temperature sensor in the top of the flue pipe to measure stack temperature. This is a key data point for determining efficiency.

Day 4                                          

John Ackerly on opening day, welcoming everyone and talking about how automated stoves can solve many problematic issues issues that come with widespread wood burning.

From the left to right - Ellen Burkhard from NYSERDA, Lisa Rector from NESCAUM, Amanda Aldridge from EPA and Mark Knaebe from US Forest Service.

We spent hours in this room, having different presentations every hour, with lots of discussion and debate. Here, Ben Myren is presenting the testing results of the VcV stove.

Brian Gauld of New Zealand, John Pilger of CSIA and Jeff Hallowell of ClearStak.

Team Wittus Twinfire

Gregory Elliiot and Peter Cullen from Wohler, and John Pilger from Chimney Safety Institute of America.

Ingo Hartman, measuring glass temperature on his Twinfire stove.

We managed to find a BYOB restaurant which led to more red wine consumption. From left - Rod Tinnemore, Dave Misiuk, Amanda Aldridge, John Ackerly, Norbert Senf, Ellen Burkhard and LIsa Rector.

Final Day

The Catalus Ventus shows incredible hot catalyst temps compared to the both the stack and the firebox. This was during start up, when it was emitting maximum smoke, but between the catalyst, the fabric filter, virtually no smoke came out the stack.

Ivana Sirovica, a Research Fellow from Alliance for Green Heat, and Ben Myren, as Ben finished the final test of the week.

Tom Butcher using the Wohler particulate analyzer on the VcV stove. Because we used wood that was often above 25% moisture content, we had to deal with more moisture in our testing instruments.

Underneath the VcV stove is where the magic happens, and mechanical valves automatically close or open the primary or secondary air, depending on what the stove needs to maintain a clean and efficient burn. THis stove maintained a steady low burn rate with beautiful swirling flames in the upper part of the chamber.

Ben Myren shows how his thermocouples could read the temperature in 10 spots of the stove at all times. The top of the flue could be 250, when the air entering the catalyst was nearly 800, and 1300 in the firebox.

Brian Gauld, the owner of the VcV travelled from New Zealand, where there is also demand for automation that can improve stove performance far more than stoves are likely to perform when operated manually.

         Dr. Phil Hopke of Clarkson University and Mattian Woll of Testo.

Our cord wood was kiln dried and then shrink wrapped so it would maintain a constant moisture content. The wood was far wetter, on average, than wood used in EPA test certifications, which helped us assess how these automated stoves could perform with higher moisture content wood.

Preparation of kindling for the tests.

George Wei and Yussef were two of Brookhavens talented technicians. Both have worked on improving oil combustion systems, outdoor wood boilers and stoves.

The last stove is taken out, and demonstrates the challenge of testing the same day as removing stoves that are still hot!