How to inspect a wood stove: A visual guide for safety & performance

Updated October 2024

The Alliance for Green Heat developed a visual guide for inspecting wood stoves for the energy audit and weatherization community as those communities have lacked appropriate training in how to inspect stoves.  Safety inspections of wood stoves are supposed to be required for all stoves, whether they are primary or just occasional heaters for DOE funded programs, such as for low-income homes covered by WAP – the Weatherization Assistance Program.

Download visual guide here

This easy-to-use guide provides photos of the most common safety issues found in wood stoves that should be checked by energy auditors - as well as other energy and hearth professionals.  It can also be useful for homeowners.  Coming soon is a checklist that will indicate the status of each item and whether it needs repair.  The guide is broken down into what needs to be checked on the exterior of the stove, the interior of the stove, the exterior of the house - and many special circumstances.  Some items are in grey areas of what an energy auditor is responsible for checking - such as the storage and moisture of the firewood - and we encourage states and counties with high rates of wood stove installations to engage in a more expansive audit.

The problem is that there is little evidence to indicate that stoves are being inspected in a meaningful and consistent way within many WAP programs.  Most states use forms that provide many options to add detail about the inspection of a furnace, but little or none for wood stoves.  Some states list wood stoves as a heating appliance and a few states, like Idaho, ask if the stove is “operable, failing or inoperable.”  Furnaces on the other hand are turned on and have their flue gases tested, producing a written record on CO, PM, temperature efficiency and draft.  This provides useful, objective indicators of the health of the furnace or boiler.  There is no corollary data input options for wood stoves that would provide a written record showing the stove had received a meaningful or even minimal inspection.

 

In recent weeks, AGH did PowerPoint presentations to two important stakeholder groups: the DOE WAP Training Consortium and the National Residential Wood Smoke Workgroup.  Both of

Download PowerPoint here.

these presentations were very productive and led to substantive follow-up work with many of the attendees.  Kelly Cutchin who heads up the WAP Training Consortium has been particularly helpful as AGH navigates the bureaucracy that surrounds WAP standards, update, trainings, etc.  

 

But while this project has gained a lot of traction and improvements are happening, we are still far away from our goal: changing the standards that the DOE uses to approve state work specification documents that have minimal attention to wood stoves.  Most states are not living up to DOE requirements that all heating systems be inspected and repaired, as needed, or possibly replaced. One problem is that DOE regulations provide far more specificity about fossil fuel furnaces and boilers. For example, “WPN 19-4 Revised Energy Audit Attachments”, a key guidance document for the Weatherization Program, mentions boilers 19 times, furnaces 21 times, and wood stoves only 1 time. The result permeates the inspections and attention that each heater receives throughout the value chain. Thus, in the sections about repairing heating equipment, there is no guidance about how to repair a stove, while there is a long list of things relevant to boilers and furnaces. This continues year after year, despite the fact that there are more wood stoves than residential boilers in the United States (around 9 million homes are heated with oil, gas and propane boilers, while 10.1 million wood stoves provide primary or secondary heat nationwide). 

There are plausible explanations for why WAP materials often have far more detail about inspecting and repairing furnaces compared to wood stoves. First, wood stoves are more often than not, a secondary heater, where furnaces are almost always primary heaters. Second, wood stoves are very infrequent in urban areas and in southern states. And third, there could be an implicit bias against wood stoves by agency officials who view them as a relic of the past and underestimate their numbers, safety issues and their importance for the rural poor.

The integration of wood heaters more fully in the WAP program ultimately should include changes to state “Standard Work Specifications” (SWS) documents, which are updated every 5 years to assure they reflect industry-accepted practices. Significant updates in the area of combustion safety occurred in the last 5 years but it is unclear if wood stoves were included in any significant way.

 

Sometimes, WAP documents say little more than a stove should be replaced if it shows “structural failure.” Some states seem to interpret that as having a crack in the heat exchanger, which in the case of a wood stove means a crack in the body of the stove. Maine is more restrictive and says replacement is "allowed only when there is a crack in the heat exchanger than may cause a carbon monoxide problem or a fire danger."  Montana is unique and at the opposite extreme where non-EPA certified stoves are considered de facto "unsafe for program purposes." 

 

Changes in these DOE funded programs will also influence the way that states, utilities and private companies conduct energy audits.  When AGH polled its supporters who have had energy audits recently, a majority said their wood or pellet stove was completely ignored.  Considering so many wood stoves are self-installed, this oversight is ripe for change.

 

Many thanks to everyone who has been working with AGH on his project, and special thanks to the CSIA, EPA and the WAP Trainers Consortium.

For further reading:

Common Problems – and Solutions – for Self-Installed Wood Stoves, Oct. 2024

Identifying Barriers to Integrating Wood Stoves in WAP Energy Audits and Weatherization Programs, Oct. 2024

Wood stove inclusive energy audit standards still missing in America, Aug. 2021
BPI Energy Auditing Standards Open for Public Comment, Oct. 2013
Unsafe Wood Stoves Routinely Overlooked During Energy Audits, May 2012

Stove Repair Relief Fund to aid families during Coronavirus pandemic

The Alliance for Green Heat is starting a fund that will help families struggling during this pandemic keep their stoves running and operating safely.  Together with the Osprey Foundation and Stove Parts 4 Less, we are launching The Stove Repair Relief Fund!  Please consider becoming a partner in this effort. 

The Stove Repair Relief Fund provides large discounts on stove parts to people who lost their jobs due to the coronavirus pandemic. With an initial fund of $20,000 provided by the Alliance for Green Heat, Stove Parts 4 Less, and the Osprey Foundation, eligible customers will receive 30 – 50% off of their parts orders. The intent is to provide essential stove parts to lower-income families who may not be able to afford to keep their wood or pellet stoves working.  It often only takes a small part to get a pellet stove back up and running or make a dangerous wood stove safe again.  

If you are a verified low-income household or have been laid off due to the pandemic, you are eligible for a 30% discount (15% donated by the Alliance for Green Heat and 15% by Stove Parts 4 Less). If you are from a verified low-income household and have been laid off, you are eligible for a 50% discount on your needed parts (25% donated by the Alliance for Green Heat and 25% by Stove Parts 4 Less).

Please note, this offer is only good for wood or pellet stove parts orders up to $500.  It is not applicable to any grill parts, gas stove parts, new stove installs or orders over $500.  If your household has been hit hard by this pandemic and you need a stove part, provide all required information on the sign-up page here to determine if you are eligible.

We are doing a soft launch of this program at the end of this heating season to assess how it works.  We hope to improve and relaunch it this fall during the upcoming heating season.

The program funders want to ensure that the funds are used to help people who really need it, and are asking people to provide documentation of their employment and economic status.  In addition, funders do not want to subsidize the sale of any parts that are available cheaper elsewhere.  Customers should check prices and ensure that Stove Parts 4 Less is offering the best price, which they usually do (make sure to also include shipping and consider the reputation of the seller for aftermarket parts). They will also match any price.  

The Alliance for Green Heat does not normally partner with or endorse specific companies, but these are not normal times.  Our staff, working with our Board, has done their due diligence to move forward with this program and will re-assess it this summer and publicly share that assessment.

We expect this pandemic to severely impact rural wood heating communities for up to a year, and many may turn to wood heating even more than in previous years.  It may also make people less likely to buy new stoves, and need to keep repairing their old ones for longer.  Pellet stove repair and maintenance has always been a challenge, and dealer training and support for older pellet stoves is often poor.  If stove dealers, NFI or CSIA technicians can't access a part elsewhere, they can alert low income clients of this program.  AGH always recommends that stove installations are completed by professionals, but basic repairs and maintenance are often done by stove owners.  If any repair has safety implications, please consult or hire an NFI technician or other professional before trying to do it yourself, even if you procure the part yourself.

The Alliance for Green Heat and Stove Parts for Less are doing everything we can to keep our employees and local communities safe, and we ask that you try and do the same.  Stay home when possible, cover up your nose and mouth with a mask or scarf and do not host large gatherings.  Save lives and give our medical professionals, first responders and people working in essential businesses a break!

Want to do your part too? Support the Stove Repair Relief Fund!

You can donate too!  To help struggling families who heat with wood and pellets, you can make a tax-deductible donation to the Stove Repair Relief Fund via the Alliance for Green Heat.  Any contributions to support this cause will be matched dollar for dollar by Stove Parts 4 Less, up to $10,000!  Please contact us if your company or institution wants to partner in this effort or has ideas on how to improve it.  100% of all donations will go to helping low-income families in this time of need.

Results of the 2018 Wood Stove Design Challenge

 By John Ackerly

The first day of testing, showing Ben Myren Prof.
Phil Hopke and Rebecca Trojanowski.
Photo: Kittner/BNL.

Conducting rigorous and transparent field testing of thirteen stoves in five days is a feat that is unheard of in the wood stove community.  The goals were also unique: fairly test stoves against one another with cordwood; help each team to improve their units and help educate a wider public about novel stove technologies that challenge how we think about the traditional, manually operated EPA certified wood stove.

The 2018 Wood Stove Design Challenge took place from Nov. 9 - 13, featuring 10 stoves in competition and 3 showcase stoves. The stoves were selected and judged by members of the

Large screen monitors provided real time data during
a test run of the Integrated Duty Cycle fueling
protocol under development. Photo: Kittner/BNL

Organizing Committee.  The Alliance for Green Heat (AGH) was the principal architect, organizer and host of the event.  Each of the 10 competition stoves received a $10,000 grant made possible by the DOE's Bioenergy Technology Office.

The Wittus team from New York
and Germany. Photo: Kittner/BNL

In the automation stove category, there were three market ready stoves that successfully went through a rigorous fueling protocol and proved that they could burn relatively cleanly and efficiently even when an operator tried to turn down the heat setting too far and at the wrong times.  An SBI stove and the VcV stove that had been in development for many years showed the value of multi-year R&D and testing, resulting in stoves that may only cost $500 more than a similar,

Staffers from EPA, DOE, USDA and Congressional
offices were able to learn about stove testing and
 engage with teams and judges. Photo: AGH

  

non-automated version.  To us, this is a major breakthrough and stoves like these should show a path to far cleaner cord wood heating in America.  

The SBI team. Photo: Kittner/BNL

The other automated stove was a German-American unit that heated water, made electricity and provided a living room fire experience with a downdraft flame into a lower chamber. While this was not an affordable stove to most Americans, it could have a reasonable pay-back over a number of years, depending on the users cord wood price.  This stove impressed both the Brookhaven National Lab and the Masonry Heater Association testing teams with ultra-low carbon monoxide numbers in the single digits under some conditions, and ultra-high efficiency.  

Ben Myren, one of the top wood stove testing experts
in the US, talking with Larry Brockman of the EPA's
BurnWise program.  Photo: Kittner/BNL

Automated stoves are regarded as one of the best, and only ways to help ensure that manually operated EPA certified stoves perform well not just in the testing lab, but in the homes of consumers.  For automated stoves to start gaining a foothold in the market federal, state and local government recognition and support will be required.

An automated pellet boiler by Maine Energy Systems capped with a Stirling Engine was the most

A Tesla owned by Osprey Foundation head, Bill Clarke,
 being charged by Maine Energy System pellet 
boilers with a Stirling engine. Photo: Kittner/BNL

futuristic of the entries, especially since it was charging a Tesla car in front of the tent. This compact unit could heat a business or multi-family dwelling and provide up to 5 kW of electricity.  

The five testing teams used different equipment
to gather a variety of data. Photo: Kittner/BNL

In the thermoelectric category, the judges concluded that “the most innovative thing is that almost all teams used commercially available thermoelectric modules and showed that it is feasible to generate useful electrical energy without sacrificing the energy efficiency or impeding the heat quality of

This is a Swiss-made electrostatic precipitator for
residential wood stoves that reduced PM by 50 -
90% in our testing.

the wood stove.  Most designs returned the waste heat after electricity generation into useful radiant heat into the room to increase efficiency.  These designs prove that the woodstoves is a good potential commercial opportunity for thermoelectrics to generate useful electrical energy and also increase their commercial appeal for consumers.”

It was clear that stoves or boilers with Thermoelectric Generators (TEG) could produce 100 to 250 watts of power. While this is a relatively modest amount of electricity, larger automated stoves or boilers operating 15 to 20 hours per day may help supplement limited solar power output during winter months. 

Fred Legget of Vulcan Energy 
with a TEG adapted to a Wiseway.
Photo: Kittner/BNL

The George Washington University, Unforgettable Fire and ASAT teams all successfully used off the shelf technology, while TEG expert Fred Leavitt of Vulcan Energy used commercially available TEGs by Hi-Z, and adapted the gravity fed Wiseway pellet stove to get a more steady 130 watt output. 

The Wittus cord wood stove was by far the most market ready and was able to make 250 watts, and it peaked at over 300 when using low moisture pressed wood logs.  Ken Adler, AGH’s Program Director of Thermoelectrics, coordinated the thermoelectric side of the competition and the thermoelectric testing.

University teams have been a key part of the Design
Challenge with SUNY Stony Brook competing this year.

Scoring was done using a numeric rubric based mostly on data produced by the testing equipment but judges did have discretion to award some points based on their subjective assessment in several areas.  Judges assessed automated stoves by these criteria and thermoelectric stoves by these.

And the awards goes to …

The Wittus team won both first prizes.
Photo: Kittner/BNL

·     * First Prize for automated stoves: Wittus.  Great performance on particulate matter, CO, efficiency and safety.

·     Second prize for automated stoves: SBI. A fully automated non-catalytic stove using only 2 sensors that may only cost $500 more than if it were non-automated.

·     * First prize for thermoelectric stoves: Wittus - again;  The highest electric output of up to 250 watts, and an integrated design that can maintain stable electric output.

·     * Second prize for thermoelectric: Vulcan Energy, using the Wiseway pellet stove that produced more than 100 watts and good PM reduction.

Stove testers Tom Butcher, Jake Lindbeg, Rebecca 
Trojanowski Photo: Kittner/BNL

·     Innovation prize: SBI, for simplicity.  The use of only one thermocouple and a sensor on the door, enabled the designers to regulate the stove despite attempts by the testers to turn the heat demand down and make it perform poorly. 

·     * The People’s Choice Award: 509 Fabrications.  Despite being a new, small company without an extensive social media network, the 509 Fabrications pressed log stove was a consumer favorite, garnering more votes than any other stove. 

The MHA testing crew: Ron Pihl, Jim 
Schales, Norbert Senf, Mark Seymour 
and Boris Kukojl. Photo: MHA

Unique and rigorous testing

The 2018 Wood Stove Design Challenge pushed the limits of rigorous wood stove testing both in terms of the amount and variety of technology used, and the fueling protocol, which is far more rigorous than any standard fueling protocol.   More details about this will be forthcoming.  Data produced by this event will show the extent to which automated stoves can navigate fueling protocols where testers try to make stoves go into smolder mode, to see if the automation is robust enough to avoid that.  Data is also more valuable for understanding real world venting conditions, as EPA approved test labs terminate in a warm indoor space, not the colder outdoors.  

Real time emission displays allowed testers teams
and judges to learn more about performance patterns.
This shows exceptional  CO and stack temps on the
Wittus. Photo: Senf

Between Brookhaven National Lab and the Masonry Heater Association, we had up to 5 separate testing teams, allowing many stoves to be tested at once.  We

Jonathan Male, head of DOE's Bioenergy
Technologies Office introducing the awards
Photo: Kittner/BNL

also wanted to have ensure that the Brookhaven and MHA teams could  periodically test the same stove at the same time.  Norbert Senf of the MHA had worked for months to automate the Condar, and the new Condar controls worked very  well, with minimal glitches. They did three runs simultaneously with Brookhaven National Laboratory who used a diluter and Testo 380. Comparisons of the two approaches will be published at some point.

Air quality testing during the Design Challenge

During the Challenge, we monitored indoor and outdoor air quality to get some sense of the impact

Tinted stove pipe donated by Olympia Chimney, 
showing mostly invisible smoke during the event
Photo: Kittner/BNL

from 9 – 13 wood and pellet stoves operating under one roof.  We used a Thermo Scientific pDR-1500 Aerosol Monitor, an Speck indoor PM monitor and a Purple Air PA-II - SD monitor.  Results were mixed, with most indoor readings between 20 - 35 micrograms per cubic meter, but with far higher spikes. The EPA short term PM standard is 35 micrograms per cubic meter.  Outdoor numbers were usually around

Les Otten, right, with Maine Energy Systems
Okofen Pelletmatic E-max CHP unit. Photo: MYSys

10 micrograms per cubic meter. Often the Speck showed  moderate to elevated inside the tent, but on several occasions, prototype stoves released excessive smoke into the tent – and outside of it.  We will issue a more detailed report on this. 

A note of gratitude

Julie Tucker of the USDA Forest Service, with
DOE's Jonathan Male and  AGH's John Ackerly
Photo: Kittner/BNL

 The Wood Stove Design Challenge is a collaborative process involving three major donors - the Department of Energy's Bioenergy Technology Office, New York State Energy Research and Development Authority and Osprey Foundation and scores of in-kind and volunteer partners.  Olympia Chimney and Masonry Heater Association were key in-kind partners, along contributions by West Penn Power

Dusty Henderson with the 509
Fabrications pressed wood log stove
that won the People's Choice Award. 

Sustainable Energy Fund, HPBA, Schott-Robax, Lignetics, Chimney Safety Institute of America, Society for American Foresters, National Fireplace Institute, Catalytic Hearth Coalition, Biolite local sweeps and installers and others were key in enabling the event to occur.  

Unless otherwise noted, photos taken by Sam Kittner and made possible by funding from Brookhaven National Lab and can be used freely by all, with attribution to "Sam Kittner for Brookhaven National Lab."  Photos attributed to AGH can also be used freely and attributed to "Alliance for Green Heat."

The GW University Team. Photo: Kittner/BNL

The innovative rocket stove entry from
ASAT being tested by Ben Myren
Photo: Norbert Senf

Our tent was right between the Capitol and the Washington Monument.
Photo: Kittner/BNL 

Photo: Kittner/BNL

HEPA Air Filters Show Good Results at Reducing Indoor Wood Smoke

By Diane Peng and John Ackerly*

Alliance for Green Heat
Updated: Jan. 2017

If you smell wood smoke in your house, you should go to the source and fix the problem. But if the source is a neighbor’s stove or outdoor wood boiler, it can be very difficult to solve the problem.  Recent research suggests that a high-efficiency particle air (HEPA) filter can reduce indoor wood smoke by up to 60%. Even small amounts of smoke from backpuffing when you open your stove to reload it can pose a health concern and may warrant the investment in a HEPA air filter. 

A 2016 study by the Department of Energy found in-home HEPA filters to reduce particulate matter (PM) by 16 - 50%. It also found that replacing an old wood stove with a new, certified one could reduce indoor PM by 36 - 53%.  However, studies found that in a third of the homes where stoves old stoves were replaced with new ones, there was no change in indoor PM levels.

This highly rated Whirlpool HEPA air
filter cost under $300.

Wood smoke contains two types of pollutants that that are of major concern, particulate matter and carbon monoxide (CO). Particulates from wood smoke  range in size from 0.01 to 0.1 microns and can penetrate deep in the lungs, causing respiratory ailments. Carbon monoxide is a colorless, odorless, and tasteless gas that can be lethal when concentrations grow high enough in contained spaces. Having a working carbon monoxide meter in your home is vital to your safety. Fortunately, carbon monoxide is unlikely to be a problem if the smoke is from your neighbor’s stove or boiler, because the concentration will be too low.  An air filter will help reduce particulate matter.

Many air filters claim that they are effective at reducing particulates including from wood smoke, but only HEPA filters have been proven to be effective.  The June 2012 issue of Consumer Reports rated HEPA air purifiers and found the Whirlpool AP51030K ($300) and the Hunter 30547 ($260) to the most effective and “Best Buys.”

Fireplaces are much more likely to cause
indoor wood smoke problems than wood
stoves.  Your nose is an excellent instrument
to tell if smoke is leaking into your home.

Indoor air pollution poses a real threat to human health. The air we breathe inside our homes can be filled with dust, pollen, animal dander, smoke, and many other physical and chemical pollutants, sometimes making indoor air more harmful to our health than outdoor air. Simply opening a window and providing ventilation can reduce the amount of pollutants inside our homes, but when this solution is not sufficient, many turn to indoor air filters.

Air filters direct air through a filter that removes any suspended particles. They can be portable units for individual room purification or cartridges that are installed directly into the home’s HVAC (heating, ventilation, and air conditioning) unit for home purification. The filter itself can be made out of a variety of materials: foam, cotton, fiber, and synthetic fibers. Pleated fibers work best because they provide greater surface area for which to catch the pollutants. One major limitation to air filters is its inability to filter larger particles because they settle from the air before reaching the filter. It is also important to note that these types of filters remove particle pollution only; gaseous pollutants such as carbon monoxide will not be removed from the air.

Filter efficiency is measured by the minimum efficiency reporting value (MERV). MERV values range from 1 – 20 with higher scores corresponding to more efficient removal of particles. High-Efficiency Particulate Air (HEPA) filters have MERV values ranging from 17 – 20 and have met the U.S. Department of Energy standard of removing 99.97% of particles greater than 0.03 microns from the air that passes through. HEPA filters are not traditionally installed in a home’s HVAC unit but are found in separate filtration devices.

Both old and new wood stoves can leak
smoke into the home.  Its often the installation
and the chimney, not the stove, responsible
for leakage. A CSIA certified chimney sweep
is an excellent resource to find and help
remedy indoor smoke issues.

Wood particles are between .01 and .1 micrometer.  One source gave the average at 0.07. According to the EPA, HEPA filters can filter particles as small as 0.03 micrometers in size.

Researchers from the University of Montana and other experts published a paper, “Evaluating the Effectiveness of a Commercial Portable Air Purifier in Homes with Wood Burning Stoves” in the Journal of Environmental and Public Health in 2011 and found that a portable HEPA air filter is an effective option for reducing particle concentrations in homes that use wood burning stoves as their primary or secondary heating source. Particle concentrations of the homes in the study decreased 61-85%.. Another research group also found that installing a HEPA filter significantly reduced particulate pollution. In addition this group found that people living in these homes saw a 32% average decrease in their levels of C-reactive protein, a marker of inflammation and cardiovascular disease.

One thing to keep in mind is that it is always better to prevent the problem rather than try to fix it. The best solution to purifying indoor air is to remove the source of contamination. This can be hard to do if the source of wood smoke inside your house is a neighbor’s outdoor wood boiler. Smoke from a neighbor’s outdoor wood boiler could very well end up inside your own home through your ventilation system.

Bottom line: If you have any level of detectable wood smoke in your house, go to the source and fix the problem.  If you can’t fix it, it is probably time to upgrade your stove and have it professionally installed, particularly if you have a stove made prior to 1988 that is not certified by the EPA.  If you can’t replace or fix the leaky stove, an air filter may be an inexpensive way to mitigate the particulate matter problem. Even with an air filter, however, carbon monoxide may still remain a serious pollutant in the home.   Given the potential negative health impacts of any prolonged exposure to wood smoke and other indoor air pollutants, there is a growing body of scientific evidence that HEPA filters may significantly improve air quality in homes effected by wood smoke and that these reductions may have positive health benefits.

Sources:

http://www.epa.gov/iaq/pubs/airclean.html

http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/air-purifiers/room-air-purifier-ratings/ratings-overview.htm

http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/air-purifiers/home-air-purifier-ratings/ratings-overview.htm

An air filter intervention study of endothelial function among healthy adults in a woodsmoke-impacted community,  Am J Respir Crit Care Med. 2011 May 1;183(9).

http://www.ncbi.nlm.nih.gov/pubmed/21257787

Hart JF, Ward TJ, Spear TM, Rossi RJ, Holland NN, Loushin BG. Evaluating the Effectiveness of a Commercial Portable Air Purifier in Homes with Wood Burning Stoves: A Preliminary Study. Journal of Environmental and Public Health. 2011 Jan: 2011: 324809

Ogulei D, Hopke PK, Wallace LA. Analysis of Indoor Particle Size Distributions in an Occupied Townhouse Using Positive Matrix Factorization. Indoor Air. 2006 Jun;16(3):204-15.

INDOOR AIR QUALITY: Wood-Burning Stoves Get Help from HEPA Filters

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3080954/

* Diane Peng was a Research Fellow at the Alliance for Green Heat and is now a medical student.  John Ackerly is the President of the Alliance.  Thanks also to edits from Derek Rogalsky, a medical student at Georgetown Medical School and the lead author of Estimating the Number of Low-Income Americans Exposed to Household Air Pollution from Burning Solid Fuels.