AGH urges the IRS to issue guidance on wood heater eligibility for tax credits

Thank you for this opportunity to provide comments.  IRS guidance on wood heaters is long overdue.  The Alliance is an independent non-profit organization that strives to represent the interests of consumers of wood and pellet heaters.  We believe a tax credit for wood and pellet heaters is essential as we transition from fossil fuel to renewable fuels. 

The IRS asked whether guidance needed to define the term "thermal efficiency rating"? If so, what testing procedures should the Treasury Department and the IRS consider requiring or permitting to be used by manufacturers to measure thermal efficiency and demonstrate ratings that are valid for purposes of the § 25C credit?

 

Summary: 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.  

 

Using the EPA database to determine eligibility is the most effective solution from a variety of public policy perspectives but it is not without problems: multiple test methods result in disparate EPA seasonal average efficiency results for wood and pellet boilers, which are not comparable, and which are not helpful for consumers or for the purposes of setting an efficiency threshold for the tax credit.  The EPA is aware of the problem but an impending change in IRS guidance on wood heater tax credits is likely to hurt members of the industry who sell some of the most sophisticated modern wood heating equipment.  We urge the IRS to consult with the EPA on this problem and find a solution as soon as possible.

 

In addition, we urge the IRS to make it clear that the $2,000 tax credit for wood heaters is in addition to the $1,200 for other 25C qualifying home projects, not instead of them. The IRS should clarify that the full $3,200 is available to taxpayers. We also urge the IRS to confirm that 25C tax credits are available to renters, not just to owners of residences, based on the removal of the term “owner” by Congress.

Finally, the IRS asked for comments on certification or other requirements for home energy auditors.  We urge the IRS to affirm that when energy auditors are directed to inspect HVAC systems, that wood and pellet heaters are recognized as legitimate heating devices and need to be inspected for safety based on nationally recognized criteria, just as other heating systems are.  Various agencies and institutions such as DOE, NREL and BPI have begun to address this problem but wood heater remain marginalized, leaving many older, self-installed units that pose fire hazards and are not being properly inspected.

Background on wood and pellet heater testing: There is universal acceptance among test labs and manufacturers that efficiency is measured using in accordance with CSA B415.1-10.  When stoves are tested for EPA certification, the traditional test is to use the EPA’s “Method 28” which consists of 4 burn rates, from low (Category 1) to high (Category 4).  The lowest burn rate allows the lowest amount of air to flow through the stove and typically produces a higher efficiency.  High burn rates allow maximum airflow through the stove, and typically produce lower efficiencies.  The labs then combine these 4 efficiency numbers and produce “a weighted average efficiency” which is what is recorded on the EPA database of certified heaters as “overall efficiency.”

CSA B415 produces three types of efficiency: Overall efficiency, combustion efficiency and thermal efficiency.  The EPA uses Overall Efficiency to get an Average Overall Efficiency” and EPA guidance on testing deficiencies makes no reference to “thermal efficiency.”  Even within the wood and pellet heater industry, there is confusion between the terms “overall efficiency,” “thermal efficiency” and “weighted average efficiency.” The image below is an representative example of how test labs report efficiencies.  

Each of the four burn rates produces an overall efficiency number, and combustion efficiency number and heat transfer, or thermal efficiency number.  The EPA averages the four overall heating efficiency numbers to get a weighted average efficiency.  In the EPA database, this weighted average efficiency is in the column titled “Overall efficiency- HHV.” (The EPA used to use the term “Actual measured efficiency CSA B415.1 after they stopped using default, estimated efficiencies in 2015.)

There are eight labs approved by the EPA to conduct certification testing, including one in Canada, Czech Republic, Denmark and Sweden.  The labs do not use efficiency terminology consistently, and often just refer to “efficiency” rather than “overall efficiency” or “weighted average efficiency” rather than “weighted average overall efficiency.” All labs clearly distinguish HHV and LHV, and no lab uses “thermal efficiency” in their weighted averages, as far as we know.

However, some manufacturers will use “Heat transfer efficiency” otherwise known as “thermal efficiency” numbers to qualify models for the tax credit because they tend to be 1-2% higher than “overall efficiency.” Thus, if a stove has an average overall efficiency of 75%, it could have a single burn rate as low as 69%, using thermal efficiency numbers.  No manufacturer uses combustion efficiency for purposes of the tax credit as far as we know.  Combustion efficiencies tend to be in the 96-98% range.

Wood heaters are tested by EPA approved labs and then the EPA uses the data in the report to certify the stove for sale. Once it’s certified the EPA puts summary data on its Database of certified wood heaters. Since 2015, the EPA has also required manufacturers to post the non-confidential parts of their lab test report on their website.  Those reports are public and you can find the efficiency numbers for each burn rate, but they are not easy for consumers to navigate. On the contrary, they are dense, full of fine, highly technical jargon and are only used by regulators and experts.

Statistics: Currently, 25 of the 31 central wood heaters are eligible for the tax credit, using the EPA list.  113 of the 262 room heaters are above 75%, using the EPA list.  Overall, that would make about half of all heaters eligible, if the IRS were to use the efficiencies listed on the EPA database.

Public policy considerations: To achieve a level of transparency for the consumer, using the EPA database of certified heaters is an obvious solution.  Some consumers care about efficiency and the only place that consumers can make side-to-side comparisons is on the EPA database.  With pellet stoves, efficiency typically matters more than wood stoves because unlike cordwood, all pellets must be purchased, and a more efficient stove can save consumers by using less fuel.

If the IRS wants to be more lenient with manufacturers and allow more than about half of heaters to qualify, it could keep allowing manufacturers to issue certificates without any guidance, or specifically say that if any burn rate achieves 75% efficiency or more, it can be eligible for the tax credit.  If the IRS specified this, we expect all manufacturers would quickly adopt this system and about 80% or more of appliances would be deemed eligible.

Public policy is also served by setting a level playing field for all manufacturers, instead of allowing some brands to undercut others by claiming their units are eligible for the tax credit when they are below 75% on the EPA database.  Almost all US manufactures now use the EPA database to determine if their models are eligible.  

By setting an efficiency threshold for wood heaters, certain types of wood heater benefit.  The Alliance for Green Heat has monitored the changes to efficiency in wood heater for more than 10 years and documented the various ways that manufacturers claim that their stoves are eligible for the tax credit.  The averages below were calculated several years ago, when efficiencies were lower but the conclusion is remains the same: hybrid wood stoves have on average, the highest efficiencies are virtually all of them qualify for the tax credit, under any definition.  More manufacturers are building hybrid stoves in order to qualify for the tax credit and whereas there were only 6 models several years ago, today there are at least 21. Non-catalytic stoves, the cheapest, most popular, and most basic stove, have the hardest time reaching 75% efficiency. Today, only 15 out of 113 non-catalytic models are 75% or over.

From a public policy perspective, setting a 75% efficiency minimum, using the EPA database of certified heaters, is positive in that it tends to favor stoves that emit fewer particulate matters (PM) emissions.  Non-catalytic stoves tend to have higher emissions both in the lab and in the hands of homeowners if other factors are equalized such as moisture content of wood and ability of the operator. Pellet stoves and hybrid stoves tend to the cleanest, as used by homeowners.

Many taxpayers want to be able to download a certificate of eligibility to keep in their files, and taking a screen shot of the EPA list may not be as easy or feel as secure. The owner’s manual of the stove almost always has the weighted average efficiency, so that can also serve as proof of eligibility for the taxpayer.

There are two classes of heaters that would be unfairly penalized by an IRS requirement to base eligibility off the efficiency numbers in the EPA database.  The first is that multiple test methods result in disparate EPA seasonal average efficiency results for some indoor wood and pellet boilers which are abnormally low and are not comparable to other boilers or helpful for consumers or for the purposes of setting an efficiency threshold for the tax credit.  The EPA is aware of the problem, as is NESCAUM and NYSDERDA who are involved in testing programs to try to identify the calculations and assumptions leading to this problem and then find a solution.

The second are Masonry heaters are also penalized but since they do not yet have a pathway to EPA certification, the solution is more complicated. There are consistent and reliable ways to test factory-built masonry heaters and those manufacturers could issue Certificates of eligibility for the tax credit, but they will not be listed on the EPA database.  Standard combustion chambers used in site-built masonry heaters could also be tested but this is more complicated.  The Masonry Heater Association is the point group on this issue.

IRS options

The IRS has several options, depending on what their goals are.  

 

1.     The first, and best option, in our opinion is to use the “overall efficiency” numbers listed on the EPA database of certified wood heaters be the sole arbiter and end the practice of using manufacturer certificates, or only allow manufactures to issue certificates for heater models that are listed at 75% efficiency or higher on the EPA database. Many of the benefits of this are discussed above in the public policy discussion.

 

2.     There is a hybrid option of allowing manufacturers to issue certificates of eligibility if a model exceeds is 75% efficient or over for stoves and outdoor boilers or furnaces, or is 75% or more overall efficiency on any of their burn rates for indoor boilers or furnaces. 

 

3.     There is the current system, where manufacturers self-issue a certificate to declare that a particular model is eligible, sometimes without any reference to efficiency figures or definitions. This has resulted in manufacturers claiming models with weighted average efficiencies as low as 64% to be eligible. This has also allowed manufacturers to claim units that are not EPA certified to be eligible without providing any efficiency data. Another weakness of this option is that there is no agency with the time, resources, or agility to provide enforcement in this area, leaving consumers vulnerable to false claims. 

 

On the following pages, we have included representative samples of four types of manufacture certificates of eligibility for the tax credit.  The disparity of the language used and the range of models that are claimed to be eligible for the credit show a clear need for more guidance for the IRS.

 

A. Example of a certificate that claims eligibility without reference to efficiency, even though it appears all units are above 75% efficiency based on the EPA database.

 

B. Example of a company that claims its units are eligible, even though they are well below 75% on the EPA list and do not meet 75% even on individual burn rates.

 

C. Example of EPA non-certified stoves without EPA approved third party lab efficiency data to claim eligibility.

 

D. Example of a certificate that claims models are eligible solely because they are “qualified energy property” with no reference to efficiency.

 

A Review of Wood and Pellet Stove Efficiency Ratings; More Manufacturers Posting Verified Efficiencies

As of May 15 2020, all certified wood stoves, boilers and furnaces are required to have a tested efficiency.  This blog discussed the period leading up to May 15, when some heaters had verified efficiencies and others did not.

April 10, 2020 - The number of wood and pellet stoves with verified efficiency numbers on the EPA’s list of certified wood and pellet stoves is soaring as we approach the May 15 deadline, when all stoves in production are required to post their efficiency.  This gives those consumers who really care about verified efficiency numbers many more options. There are now 296 stoves, nearly half of all stoves, that have verified, actual efficiency numbers.  The EPA list of stoves is the definitive source for efficiency numbers as most most stove company websites use exaggerated, misleading efficiencies.

Among the 296 stoves with actual efficiencies, hybrid, catalytic and pellet stoves are the most efficient, averaging 77% efficient for cat stoves and 78% for hybrids.  The average non-catalytic stove is 71% efficient and the average pellet stove 74% efficient.  Pellet stoves also have the greatest range, from 58 to 87% efficiency, a 29 point difference with an average of 74%. Consumers should be aware of which pellet stove they buy.

Consumers should should be especially aware that many stove companies issue Certificates claiming their stoves qualify for the federal tax credit, even though they are far below the required efficiency.  The IRS requires a thermal efficiency rating of 75% but in the absence of any apparent IRS oversight, companies are claiming stoves with efficiencies as low as 59% qualify.  Jotul claims all of their stoves qualify, including their F370 listed at 66% efficiency.  Hearth & Home Technologies claims their Quadra-Fire Classic Bay 1200 qualifies at 63% efficiency.  Neither company replied to AGH inquiries.  The industry association, HPBA, would not comment on how manufacturers should calculate efficiency for the tax credit.

Kuma now holds the distinction of having the highest rated efficiency of any wood stove at 84%, tested with crib wood and the highest tested with cordwood, at 81%.  Enerco, a Cleveland Ohio compnay and ExtraFlame, an Italian company, have the highest rated pellet stove efficiencies at 87%.  Enerco's model, sold under the Cleveland Iron Works label, is a budget model sold in big box stores, as are the PelPro stoves that are above 80% efficiency and have a solid reputation for durability.

The EPA dropped the estimated default efficiency numbers on their list of certified stoves in 2015, an acknowledgement that those default numbers were both inaccurate and not helpful to consumers. (They used to assign 63% efficiency to non-cat stoves, 72% to catalytic and 78% to pellet stoves.) As of 2015, the EPA does not maintain or endorse any efficiency default numbers.

The Alliance cautions consumers against relying on stove efficiency claims posted on manufacturers websites. Most manufacturers post efficiencies numbers using a variety of non-standardized calculations. Virtually all post efficiencies using the European lower heating value (LHV) standard.  A 75% efficient stove using LHV would be about a 70% efficient stove using HHV if the wood was at 20% moisture content. (See this Wikipedia page for more about the difference between LHV and HHV.)

Even if a company has a verified, third party efficiency value on the list of EPA certified wood stoves, many companies will continue to list efficiency values far higher on their own websites, where most consumers get their information.    Only a handful of companies, including Blaze King, Kuma, Seraph, Travis and Woodstock Soapstone, provide the same efficiency number on their website as the independent lab reported to the EPA.  Fewer companies list their official EPA test report on their website next to their product, as required by the EPA.  Exceptions include J.A. Roby, Kuma, and Jotul.  Click here for more on brands that consumers can trust.

The EPA started to require stoves to be tested for efficiency in May of 2015, far later than their European counterparts.   Stoves that were tested and certified before May 2015 did not have to disclose their efficiency until they are required to test again, which will be 2018-2020 for many stoves.  Some of the stoves listed here were done so voluntarily by manufacturers, not because they were required to.  Pellet stove companies in particular appear to be least willing to share verified efficiency numbers with consumers, possibly because their efficiency numbers are lower than the could be.

The EPA began issuing a voluntary hangtag to stoves that meet the 2020 emission standards early, disclose their actual efficiency and meet a variety of other disclosure requirements.  Many of the stoves on the list above will be eligible to display that hangtag on the showroom floor and the Alliance for Green Heat urges consumers to consider buying stoves that display the hangtag.  Stoves sold by Blaze King, Travis and Unforgettable Fire are now approved to display this hangtag and more companies will be approved soon.

How important are efficiency listings?

Tested efficiencies of wood stoves give an indication of how efficient the stove can be when it is operated well with seasoned wood.  Efficiency and emission numbers achieved in a lab under optimum conditions are likely the best numbers that stove can achieve, not an expected average that a consumer will get.

Unseasoned wood that is over 25% moisture content will dramatically lower efficiency.  More important than a 5% difference in tested efficiency is burning your stove with seasoned wood and with enough air to the firebox.  Even the most clean and efficient stove can be polluting and inefficient if it is not operated well.

For pellet stoves, the lab tested efficiency numbers are more representative of efficiencies you get at home, assuming you keep the stove clean.  A dirty pellet stove that has not been serviced for more than 6 months is likely to get lower efficiency.

Wood Stoves with Verified Efficiencies

The non-catalytic stoves on this list range from 60% to 77% efficiency, the narrowest efficiency range of any class of stoves.  Catalytic and hybrid stoves range from 63% to 84% efficiency.  Pellet stoves range from 58% to 87%, the widest efficiency range among different types of stoves.

The Vermont Castings Encore
is a hybrid stove that does not
have a verified efficiency on
the EPA list, but they use one
on their showroom hangtag.

Some companies are claiming verified efficiencies on their showroom hangtags but it is unclear if these are actually verified, HHV numbers.  Vermont Castings, for example, and the hangtag in the showroom shows their purported tested efficiency but they have apparently not provided the a verified efficiency to the EPA for the list of certified stoves.

Pellet Stoves with Verified Efficiencies 

Virtually all companies that make pellet stoves now have some with verified efficiencies on the EPA list, a major shift since May 2015.  Italian company Extraflame currently produces the two most efficient pellet stoves on the EPA list, at 87% and 85%.   Aside from Extraflame, 14 other models have efficiencies above 80%.

The average efficiency of a pellet stoves is about 74% HHV,  but many popular pellet stoves are between 58 and 65% efficient. Of the nearly 170 stoves with actual efficiencies, the only ones under 60% or over 85% are pellet stoves.

For more background on this issue, see:

EPA Begins Listing Actual Stove Efficiencies

The Case for Minimum Efficiency Standards for Stoves

EPA Lists Efficiencies for Outdoor Wood Boilers

4 Reasons Why Wood and Pellet Stove Efficiencies are Usually Unreliable

Alliance Urges Consumers to Buy Stoves with Verified Efficiencies; EPA starts to list actual efficiencies

Updated: Jan. 2017

Efficiency is measured with a "stack loss
method," meaning a ratio of how much
heat stays in the room vs. goes up the chimney.

The EPA has started listing actual efficiencies on their list of certified stoves. Until 2015, the agency had only used default efficiency numbers for wood and pellet stoves, with 63% for non-catalytic stoves, 72% for catalytic stoves and 78% for pellet stoves. See a review of efficiencies of various brands of stoves.

The change allows manufacturers to submit actual efficiency numbers using the B415 test method and give consumers confidence about the efficiency of a stove. It has already spurred some competition among stove manufacturers, particularly the companies that make catalytic stoves and probably have the highest efficiency numbers in the market.  Verified efficiencies are up to 86%.

“If you want an assurance that you are buying a high efficiency stove, the best way is to buy from a company that publishes efficiencies using B415 and submits their numbers to the EPA,” said John Ackerly, President of Alliance for Green Heat. Currently, manufacturers are required to test for and post efficiency numbers for stoves certified after May 2015.  But a large majority of stoves were certified and tested before then, and are not required to disclose their efficiency numbers.  They can do so voluntarily, as Jotul, Blaze King, Kuma and others have.

Efficient stoves save money and time

New, EPA certified non-catalytic stoves are almost all within the 55 - 75% efficiency range, with most in the high 60s and low 70s. Catalytic stoves will likely be between 75% - 82%. “A 20% difference in fuel efficiency can add up to a lot of savings for consumers, whether you buy your firewood or cut it yourself,” said Ackerly.

With pellet stoves, the efficiency range is even greater and consumers stand to gain or lose a full 30% or even 40% in fuel efficiency depending on what model they buy. At least one pellet stove on the market gets only 33% efficiency and another 49%, but most are in the 60s and 70s, and some will be in the 80s. Industry leaders have conceded that most pellet stoves are not 70% efficient despite the EPA estimated default of 78% efficiency. 

Consumers buying new pellet stoves have little access to reliable efficiency information and could easily come home with a stove that is between 55 - 65% efficient. Most pellet stove manufacturers either do not supply efficiency data or supply exaggerated data that that makes their stoves appear far more efficient than they actually are. 

Most stove manufacturers do not disclose how they measure efficiency

The United States uses the higher heating value (HHV) for efficiency numbers for all appliances, whereas Europeans use the lower heating value (LHV). This makes it appear that European stoves and boilers are more efficient as a stove that is 75% HHV efficient would likely be around 83% LHV efficient. Many stove manufacturers use this discrepancy to their advantage by reporting efficiency using the LHV method, but do not disclose the method to the consumer.  

This phenomenon arose partially because the IRS approved the use of LHV numbers to qualify stoves for the federal tax credit that expired in the end of 2011. To add to the confusion, the IRS did not say how efficiency should be measured, allowing industry to use many different methods. As a result, virtually every stove in America was deemed to be at least 75% LHV efficient by the manufacturers who made them. Most manufacturers continue to use LHV numbers and whichever efficiency calculation provides them with the highest number.

Virtually no company, agency or non-profit has openly and honestly discussed this issue and tried to help unravel the confusion around efficiency numbers. One of the few websites that has anything on it is www.combustionportal.org. It says “ On February 6, 2007, the EPA approved use of the CSA B415 test protocol as a means by which to determine efficiency ratings. The IRS sponsored wood stove tax credit program allows manufacturers to use a different method of determining efficiency. IRS allows laboratories to use greater flexibility in determining the thermal efficiency rating for tax credit purposes.”

The decision by the EPA to start posting actual efficiencies on their list of certified wood stoves is a step forward to help consumers identify real efficiency numbers.  

EPA Declines to Release Efficiency Data on Wood Pellet Stoves

In July 2015, the EPA said it could not release efficiency data on pellet stoves, since manufacturers of the stoves claimed that it was "Confidential Business Information." The EPA is required to disclose emissions, but it does not necessarily consider efficiency close enough to emissions.

Pellet stoves are one of the most popular renewable energy technologies in American homes.  About one million homes use pellet stoves in the United States, yet none of the major stove manufacturers were disclosing the tested efficiency of their products. 

The EPA recently set stricter emission standards for wood and pellet stoves, but did not require the disclosure of efficiencies of stoves currently on the market.

The Alliance for Green Heat filed a Freedom of Information Act (FOIA) request with the EPA on June 3, 2015 urging the agency to release stove emission and efficiency information.  In their response letter, the EPA released detailed emission test results and other data, but issued a partial denial on efficiency information until it contacts manufacturers to see if they agree their efficiency values can be released.  To date, consumers have been left in the dark as to whether they own a 50% efficient stove or an 80% efficient stove.  

The Alliance for Green Heat filed the Freedom of Information Act Request to get more data on the certification test, the moisture content of the pellets used in the test and because of a longstanding problem with stove manufacturers advertising misleading and exaggerated efficiency claims.  The EPA has made efforts to reduce misleading efficiency claims by outdoor boiler manufacturers but not by wood or pellet stove manufacturers.  

In response to the request, the EPA released 42 pages of documents showing how 7 popular North American pellet stoves and 3 European pellet stoves were tested and at which burn rates they are cleanest.  One of the stoves was tested with pellets with only 2.3% moisture content, where most others used pellets with 5 - 7% moisture content.  Most commercially available pellets have 5-8% moisture content.  The EPA declined to provide the brand name of pellets used in testing.

Wood pellets for heating are usually
made from dry sawdust or wood chips
that are specially dried and ground up.

No federal or state agency requires manufacturers to use a common method of reporting stove efficiency in their promotional materials.  Most households use pellet stoves because they can save $500 to more than $2,000 per year instead of oil, propane or electricity.  However, the potential savings fluctuate widely based on the efficiency of the stove.

The EPA said they could not release the efficiency data because companies may consider it a trade secret and commercial or financial information that is exempt from being released by the EPA to the public.  Stove manufacturers claim that their efficiency information, along with almost all other data obtained from the certification testing is “confidential business information.” 

Testing for efficiency has not even been required by the EPA prior to 2015. The initial information released by the EPA indicates that it does have efficiency values for some stoves.

However, the EPA left open the possibility that it might release the efficiency values if the Alliance for Green Heat wants to receive a “final confidentiality determination” that would involve giving manufacturers an opportunity to substantiate their confidentiality claims.  If the EPA informs manufacturers that it agrees that efficiency information should be public, manufacturers would have to challenge the EPA in court to prevent the EPA from releasing that information.

John Ackerly, President of the Alliance for Green Heat said that the organization intends to seek a final determination from the EPA.  “Cars, furnaces and large appliances all have to report their efficiency and energy use to the public and this is a critical part of helping consumers save money and help the environment.  Why should there be a special exemption for pellet stoves?” Ackerly asked. 

“The lack of transparency on efficiency is holding back this sector, as other forms of renewable energy are quickly gaining traction,” Ackerly noted. 

The new EPA wood heater regulations will require manufacturers to disclosure the efficiency of new wood and pellet stoves tested after May 15, 2015.  However, stoves that are already on the market will not need to be tested for another 4-5 years and will not be required to disclose their efficiency until this time.  Many manufacturers obtain efficiency data during their EPA certification tests and include them in their test reports to the EPA, although they do not release them to the public.  The FOIA was an attempt to get the EPA to release this information that it already has in its files.

Pellet stoves have a very wide range of efficiencies and manufacturers may claim that if they released the actual efficiency of their stoves it cold cause substantial harm to their competitive position, which is one of the reasons the EPA withholds business information.

Stove manufacturers are also hesitant to disclose efficiency information to their consumers because if their efficiencies are under 75%, their product would not be eligible for a federal tax credit that has often been retroactively renewed and requires a 75% minimum efficiency.  Since neither Congress, nor the IRS, nor EPA requires any standardized measure of efficiency, stove manufacturers can claim that nearly 100% of stoves on the market are 75% efficient.  If the EPA were to disclose actual efficiencies, it would make it harder for manufacturers to convince consumers that all their stoves were over 75% efficient.

The number of U.S. homes with pellet stoves far outnumber those with residential solar panels by a ratio of about 2:1.  Pellet stoves typically cost $1,100-$3,500, and have a payback period of 3-7 years depending on such factors as the price of the fossil fuel being displaced, the frequency the stove is used – and its efficiency.