Wood pellet data is vital to understand contribution of pellet heating in America

 The Alliance for Green Heat submitted a public comment on the EIA's Densified Biomass Fuel Report earlier today. The EIA was gathering comments on a proposed three-year extension on the report along with specific questions on its function and use.

"The Alliance for Green Heat (AGH) would first like to thank the U.S. Energy Information Administration (EIA) and the Department of Energy (DOE) for giving the public an opportunity to submit comments on the proposed three-year extension to Form EIA-63C, “Densified Biomass Fuel Report.” As a national nonprofit that advocates for the reduction of fossil fuel heating through the responsible and sustainable use of wood and pellet heat, we are deeply invested in the outcome of the EIA and DOE’s decision to continue to collect data on pellets.

Summary: The EIA does not need to collect more information from pellet manufacturers. However, it does need to publicly release much more of the information it is gathering.

It is important for policymakers, environmental organizations, and the public to have a far more accurate understanding of the differences between how utility pellets are made, how premium heating pellets are made, and the carbon impacts of how they are used. Utility pellets have biodiversity, equity, and carbon impacts that are more serious than premium heating pellets based on their feedstock, the size and location of their manufacturing plants, and the enormous amount of waste heat that is lost when making electricity. Data gathered by the EIA provides some of the underlying metrics to understand those different impacts.

Wood pellets are an excellent low-carbon heating fuel for homes, businesses, and institutions. They will likely become an even greater complement to heat pumps in the future, based on the different pros and cons of each heating pathway as our energy grid seeks to keep up with increasing electric demand. Wood pellet production and use are also extremely important for better understanding air quality and whether states and air quality agencies have been able to increase the percentage of pellet stoves compared to wood stoves. Also, EIA data from their housing survey, part of the Residential Energy Consumption Survey, shows that wood pellets serve many very low-income homes. The 2020 data shows the income bracket with the highest reliance on pellet stoves compared to wood stoves is the $10,000 - $19,000 household income bracket. This makes wood pellets very relevant to the energy equity community.

Our industry and stakeholders have become used to seeing top-level data such as the wood pellet production capacity by region, overall production of heating vs. utility pellets, and domestic vs. foreign pellets. But to really appreciate the various roles this industry plays in providing renewable heating in America, we should all be versed in more granular detail.

For example, it is very important for government agencies, pellet stove manufacturers, pellet fuel distributors, retailers, and consumers to know the volume of:

• PFI certified domestic heating pellets made year-by-year,

• Non-PFI certified pellets made year-by-year if the percentage of bagged vs. bulk domestic heating pellets is trending up or down,

• Utility pellets used domestically,

• ENPlus A1 or A2 bulk heating pellets are made in the US (these would likely be bagged in Europe for residential distribution), and

• Compressed bricks, compressed logs, and briquettes made, year-by-year.

The EIA could also provide more detail about where wood comes from. It provides summary, top-level data, but we believe there is more data available that does not infringe on confidentiality.

A breakdown by state also tells an important story of pellet production in the United States. North Carolina, the top producer of industrial pellets for export, makes nearly as many pellets as the bottom 20 states combined - which produce heating pellets.

Response to EIA questions:

1. In response to the invitation to comment on the following statement: “(a) The proposed collection of information is necessary for the proper performance of agency functions, including whether the information will have a practical utility,” AGH would like to highlight the value that the Densified Biomass Fuel Report provides to hundreds of stakeholders in the renewable energy space who need this information to assess the capacity of this sector. The data provided through the reports helps track trends in pellet production and increases the ability to produce accurate, science- based assessments on pellet heating. Without the Fuel Report, organizations would lose one of their most reliable and unbiased information sources on pellet data.

In the energy transition landscape that our nation is currently undertaking, being able to account for, and have accurate information on, all forms of renewable energy is paramount. If our nation’s leading agency on energy information is missing data and research on a large, mainstream, and established renewable energy source like biomass, the agency is failing to carry out its mission.

2. In response to the invitation to comment on the following statement: “(c) EIA can improve the quality, utility, and clarity of the information it will collect,” AGH would like to suggest that the EIA publish more of the data that it collects. Assuming no confidentiality conflicts, we believe publishing all gathered “Product Type” information is essential (e.g. amount of “Wood Pellets Premium (PFI certified) Bagged,” Wood Pellets Premium (PFI certified) Bulk”, etc.). Similarly, publishing data on “FeedStock Type” (e.g. “Roundwood,” “Sawdust,” “Waste Wood,” etc.) would be helpful when explaining to policymakers and the public the different supply chains in the pellet industry. This is particularly important for policymakers and the public to differentiate how heating vs. utility pellets are made. This would also provide industry and organizations with a clearer vision of the current capacity of biomass for heating, helping provide decision- makers with valid, data-driven information. Because this information is already gathered in the monthly reports, this would not add any time burdens on the pellet manufacturing companies.

Wood is a diverse and vital renewable energy source for America. Many Americans do not seem to know that up until 2015, wood produced more renewable energy than any other renewable source. Since 2016, biofuels have been the top producer, but the intensive process of converting solid biomass to biofuels sharply reduces its carbon benefits.

Many Americans may also be surprised that wood still produces more renewable energy than hydroelectric solar and geothermal combined. As recently as 2015, wood produced more energy than hydroelectric, solar, geothermal, and wind combined. It is a vital part of America’s transition to renewable energy to know that the use of wood as a renewable energy has been relatively stable but shrinking since 1985, and the amount of solar and wind energy has been rapidly growing. Part of this story is understanding and managing all the different feedstocks that go into wood energy - mainly pellets, wood chips, and wood logs.

The EIA can do a better job using the data that it collects from pellet manufacturers to tell a more detailed story about wood pellets made in America and pellet heating in America."

Alliance for Green Heat and USDA Forest Service partner to expand national network of firewood banks using local, renewable energy to assist low income households

AGH, April 8, 2024 - Alliance for Green Heat is making over $1 million available to expand and connect the nation’s network of firewood banks thanks to a grant from the USDA Forest Service made possible by President Biden’s Bipartisan Infrastructure Law. Firewood banks, similar in approach to food banks, provide a local, renewable and cost-effective heating source to households in need. 

Firewood banks can start applying for funds on May 1. Banks that have already received funding can apply for renewable grants on September 1. 

The program is intended to help firewood banks expand, be sustainable, deliver seasoned wood and improve safety practices. 

The Census Bureau estimates 1.9 million U.S. households use wood or pellets as a primary heat source. In rural areas, about 25% of homes use wood as a secondary heat source. In tribal communities, wood is often the primary heat source for the majority of households.  The top wood heating states, in order, are Vermont, Maine, Montana, New Mexico, Idaho, New Hampshire, Oregon and West Virginia. 

Forest Service Chief
Randy Moore

“Firewood provides a local, renewable source of heat for so many families across our country, especially in tribal communities,” said Forest Service Chief Randy Moore. “Thanks to the Bipartisan Infrastructure Law and our partners at Alliance for Green Heat, we are able to support the network of firewood banks that are providing lifesaving aid by ensuring more families can access the firewood they need.” 

Funding mostly goes to purchase tools, chain saws, splitters and protective safety equipment. Most firewood banks receive free logs from towns, tree trimmers, loggers and other donors but some have to purchase logs. They largely rely on volunteers to cut, split, season, and deliver firewood to local households who have run out of firewood and cannot afford to buy more.

Most communities in the United States have excess wood which is thrown away. An important source of firewood comes from efforts to remove material from forests that could potentially fuel a destructive wildfire, like dead or dying trees. 

In its first two years, the grant program funded 80 firewood banks in 24 states. 31% are operated by, or primarily serve, tribes, 19% by faith-based organizations and 47% by non-profits, towns, or community groups, and 3% by businesses.  During the first two year of the program, firewood banks produced more than 20,000 cords of wood to about 20,000 homes. On average, each firewood bank produces more than 200 cords per year, with many western tribal firewood banks leading the way producing 500 to several thousand cords. Nationally, the Alliance for Green Heat has identified more than 150 firewood banks and scores more are likely active. 

Volunteers prepare wood for thousands 
of homes in nearly every US state.

“Firewood is ‘the people’s fuel’, used by rural households who can’t afford fossil fuel, or are trying to be less dependent on it,” said John Ackerly, president of the Alliance for Green Heat.  “It is and always has been an affordable way to reduce fossil fuels and back up heat pumps but the challenge is using it without producing too much smoke.” 

As of May 1, existing wood banks who served households last winter and start-up firewood banks can apply for funding.  Firewood banks seeking a second, renewal grant can apply starting in September. For more information about firewood banks and to apply for funding, visit firewoodbanks.org.

About the Alliance for Green Heat

The Alliance for Green Heat promotes modern wood and pellet heating systems as a low-carbon, sustainable and affordable energy solution. The Alliance works to advance cleaner and more efficient residential heating technology, particularly for low and middle-income families. Founded in Maryland in 2009, the Alliance is an independent non-profit organization and is tax-exempt under section 501c3 of the tax code.

 

State electrification policies and wood and pellet heating

To date, state legislation targets fossil fuel, not wood and pellet combustion

Decarbonizing residential heat generally means the conversion of fossil fuel appliances to primarily electric sources of heat. Typically, this would be high-efficient heat pumps or geothermal – but it could also involve pellet stoves.

In rural areas, wood stoves are likely to remain popular in the transition to heat pumps as a backup energy source during power outages, and they could also relieve stress on the electric grid at peak times. As states begin to pass laws to move towards electrification of homes and buildings, there is some concern that wood and pellet appliances could also be restricted, either inadvertently or purposely but AGH has not found any policies that would restrict wood and pellet combustion appliances. However, the lack of specificity in bills leaves open the possibility of contradictory interpretation at the local or county level. 

AGH has our eyes on six state-wide electrification policies, continuously monitoring movements in the legislature, code councils, or courts as they develop. Much of the current electrification movement is happening at the local level. Over 100 counties or cities have decided to adopt energy codes or ordinances that phase out the use of fossil fuels in the residential heating sector.

We suspect restrictions on wood and pellet appliances will be driven more by concerns over particulate matter (PM) emissions, which may be justifiable when it comes to wood stoves in urban areas but problematic for pellet appliances. The development of “zero emission” heating standards might also be a problem for wood and pellet technology. 

Photo Source: AGH created image to add pellet stove. Original image: Unique Heating and Cooling.

Washington D.C. is the only state-level jurisdiction that targets “on-site fuel combustion,” but it is unclear that this will include fireplaces, wood, or pellet stoves.  Given the number of exemptions that are being added to such policies, we expect technologies like pellet stoves and fireplaces are likely contenders for such exemptions.

Only one state, New York, has passed a bill that would phase out fossil fuel equipment in the residential sector, but they specifically did not include wood or pellet heaters. There are plenty of exemptions in New York’s electrification law: emergency back-up power generation, manufacturing facilities, commercial food establishments, laboratories, laundromats, hospitals, other medical facilities, critical infrastructure such as backup power for wastewater treatment facilities, and crematoriums. It also exempts the full application of the law in situations where the building code council deems it infeasible (Part WW, Subdivision 6 of section 11-104).

Closest to New York’s strategy was Washington state’s decision to adopt energy codes that would effectively phase out fossil fuel infrastructure starting in March 2024 (Section R405) and California’s vote to develop and propose zero-emission standards for space heating by 2030 (CARB, 2022). Washington’s energy code proposal does not threaten wood and pellet use, as they can be an acceptable part of a building’s overall energy performance in conjunction with a heat pump.

California’s proposal for zero-emission standards for space heating is still unclear but could possibly pose a problem for wood heating. Both require follow-up rulemaking as they move throughout committees and councils, fleshing out exemptions and practical applications. Because the gas and homebuilders industry in 2023 asked a federal judge to dismiss their case against the Washington State Building Code Council (Spokane Home Builder’s Association v. Washington State Building Code Council, No.  1:23-cv-03070-SAB), we will be able to see the practical application of the amended energy codes sooner rather than later.

New Jersey is the only state that has current legislation in progress that includes the phasing out of “unregulated fuels” in its push to electrify residential homes (S.249). We suspect the intention of including “unregulated fuels” was to target fuels like propane and oil, which are not delivered by regulated utilities, not wood and pellets. However, wood or pellets could be considered unregulated, despite their obvious role in decarbonizing the building sector. Further defining “unregulated fuels,” and identifying the goals behind that definition, will give us a better idea of how wood and pellets will fare in the future of New Jersey electrification policy.

Photo Source: Bensonwood

Massachusetts has a bill in progress that would need to be fleshed out before determining whether it could apply to wood and pellet heating (H.3183 / S.2115). “An act Relative to the Electrification of New and Substantially Remodeled or Rehabilitated Building,” states that buildings “shall use electricity instead of fossil fuels for space heating.” In some ways, this could be interpreted as still allowing wood and pellets for space heating, if it isn’t a conversion from fossil fuels. There are qualms to be had about this wording, for sure, but flexible enough to allow advocacy for wood and pellets inclusion in practice.

Wood stoves have been restricted in some urban areas and smaller towns and valleys based on concerns over particulate matter but this should not be confused with restrictions on carbon intensive fuels. AGH urges jurisdictions who restrict the use or installation of wood stoves because of excessive wood smoke to exempt pellet heaters.

Summary

AGH urges jurisdictions to consider all low carbon heating technologies, and to be sensitive to how reliant many rural low-income homes are on wood and pellet heating. We suspect it will take decades for there to be enough funding to switch most rural low-income homes to heat pumps, and even then, many households may want a wood or pellet stove back-up.

We also believe it is an important time for wood and pellet heat advocates to reach out to electrification groups and build alliances. By supporting and uniting with this movement, wood and pellet technologies have the best chance to be understood as a respected partner in the low carbon energy transition. This would also open opportunities to educate movement leaders on the critical difference between firewood and pellet use for heating versus its use in electricity generation, or its non-essential uses like in fireplaces, firepit, etc. Wood stoves also play an important role in energy poverty alleviation. The importance of wood and pellet heaters to low-to-moderate-income households is generally understood by legislators. Because of this, many states still incentivize wood or pellet heaters, as does the U.S. Congress through a federal tax credit that is at the same level of solar and geothermal.

Beyond the United States, the Alliance for Green Heat follows standards around the world that might provide some insight and creativity for policies and regulations here at home. Dan Gates, a Luths Services director/engineer in Scotland, recently published an opinion piece on Scotland’s recently adopted “New Build Heat Standard” (NBHS). Dan’s analysis of the NBHS, which would ban direct emission heating systems in newly constructed homes in Scotland starting at the beginning of this month, is similar to analyses we find ourselves undertaking in electrification policies stateside.

Dan analyzes four main points, but we think the first point is the most relatable to the electrification work AGH undertakes. He asks, “Ban on biomass but what about stoves?” In Scotland’s case, it is unclear whether wood stoves could qualify as “emergency heating.” It is likely that you would have to argue that your new wood stoves would act as your energy heating in the event of a power outage (not just as an accessory heating system in general) for it to qualify. Dan makes a point we often make in our own public comments on similar legislation: wood stoves are incredibly complementary to heat pump systems in rural areas. He argues that making an exemption for wood stoves in rural areas would be a good idea, preventing “backlash against the legislation on the main point of the regulation- to ban oil/gas boilers on new build.” Either way, clarification on this question of whether wood stoves have a place in the NBHS needs to be made.

At Alliance for Green Heat, we think it is important to keep our eyes on evolving electrification policy that could affect wood heating no matter the country. Ideas and needed clarifications are often similar to our own, strengthening the resolve and interest in utilizing wood heat in the most strategic manner in the energy transition.

Fossil fuel industry stops Maryland electrification legislation

In this year’s legislative session, Maryland lawmakers introduced a bill that would have made the Maryland Department of Labor adopt a requirement that new buildings meet all water and heating demands of a building without the use of fossil fuels, along with requirements on “solar-ready” standards and EV charging infrastructure.

The bill would also require buildings that could potentially receive a waiver of the fossil-fuel free building demands (e.g. emergency back-up power systems, commercial food establishments, etc.) be sufficiently “electric ready.” The Chesapeake Climate Action Network has reported that lobbying by Washington Gas and Baltimore Gas and Electric killed the bill before it could even come to a vote.

Photo Source: CCAN

The Alliance for Green Heat supported this bill, and others like it, because it would have helped to decarbonize residential heating, and would have allowed homeowners to pair a wood or pellet stove with another low-carbon heating appliance – the heat pump. We’ve found that wood stoves can foster confidence in those wishing to switch over to electric, giving them a sense of comfort knowing that they will have heat no matter the possible service disruptions.

“The Better Buildings Act of 2024 (SB 1023 / HB 1279) is a strong step in the right direction to decarbonize Maryland’s residential heating,” said Darian Dyer, Policy Analysis for the Alliance for Green Heat. “Our mission has always been promoting low carbon heating and giving homeowners a choice between low carbon heating options.”

This year also saw a significant setback in Maryland for low-carbon heating when the MEA abruptly announced cancelling a wood and pellet stove rebate program that mainly benefited more rural, LMI households. That program was the result of advocacy by Heather Mizeur and AGH to balance the rebates for solar panels and electric car chargers that went to mostly higher income homes in wealthier counties with a program aimed at more rural, less wealthy homes.

AGH advocates for policies that decarbonize heating without disproportionately burdening rural and low-income households. Our priority is to see that proper “guardrails” are in place to support an equitable energy transition. These guardrails involve the following:

1.     Making sure that electrification policies do not result in electrical resistance heating that are inefficient, high carbon and would particularly burden lower-income apartments and homes with high operating costs;

2.     Ensuring that wood and pellet heating remains a viable option for primary or back-up heat for electric and non-electric homes;

3.     There are mechanisms in place to support low and middle-income households to install more efficient heating technology such as heat pumps and pellet stoves.

During such policy changes in the energy field, we also support state-funded initiatives to help retrain those laborers and contractors that have found fossil fuel infrastructure work as their main source of income to set them up to succeed in renewable energy roles.

The Better Buildings Act of 2024 was an important step in a major residential decarbonization strategy, and many details still needed to be hashed out. The Alliance for Green Heat looks forward to Maryland’s legislature making the climate-smart decision in advancing something like the Better Buildings Act in the next legislative session in 2024 and welcomes the work that will need to be done to make it an inclusive, equitable standard.

Even though Maryland is a very progressive state, it still lags behind scores of other states in decarbonizing its grid and its heat. In Maryland, a great majority of homes could be heated and cooled with heat pumps, and 5 to 10% of Maryland homes could have a wood or pellet stove as a back up to a heat pump or fossil fuel furnace, or for primary heating. Pellet stoves are a sustainable and relatively clean option for almost any single family home in Maryland, while wood stoves are better suited for rural areas.

Low-cost air quality monitors excel at detecting levels of indoor wood smoke

At $39, real time PM sensor can empower homeowners – and neighbors 

Ever wonder if your wood stove or pellet stove elevates your risk of inhaling particles that could endanger your health?   Recent advances in technology now make indoor air quality monitors small inexpensive and simple for people with wood and pellet stoves - or fireplaces.  The Alliance for Green heat bought and tested several and found the Govee Smart Air Quality Monitor, at $39, to be the best.

 

The Govee Air Quality Monitor (right) shows PM, temperature and humidity on a digital display.  The Amazon Smart Quality Monitor on the rleft ($79) only has a small light indicating air quality.

Not all wood and pellet stoves result in poor indoor air quality.  But there is little research that compares different types of wood and pellet stove installations. The human nose is very sensitive and if you smell wood smoke in your home often, that is enough of a reason to look into the problem.  

 

Low-cost sensors like the Govee or the Amazon sensor (that connects to Alexa) detect particulate matter (PM2.5) and can help homeowners better understand the issue and may be a motivating factor to take action, which could mean calling a chimney sweep or just cleaning your pellet stove better before lighting it.  

In the future, such monitors could easily be built into stoves, which could be a significant advance in helping homeowners understand how to best run them.  This year, MF Fire will be introducing an aftermarket sensor package designed to help homeowners operate their stoves better, but they do not measure indoor PM.

Feb. 20. The Govee (left) and Amazon (right) are both easy to set up on your phone and see temperature, humidity, PM and CO on an hourly, daily, weekly or monthly basis. We found they correlated relatively well. They both spiked around 7 PM, cooking dinner but the Amazon did not record much of a morning spike when I lit the stove and cooked breakfast. Both calculated the daily average at exactly 3ug/m3.

On Feb. 19 both the Govee (right) and Amazon (left) monitors caught the morning start-up/breakfast and elevated evening PM.  The Govee had a 2 ug/m3 daily average and the Amazon had a 3 ug/m3 daily average.  One big benefit of the Govee is that is shows temperature on the same screen as PM, and you can see when the pellet stove is turned off around 10PM and turned back on around 6:30 AM. 

 

Digital displays are now everywhere in our homes and cars and they tell us everything from when to add air to our tires to when to change the filter on a furnace.  But for those of us who heat our homes with wood stoves and pellet stoves, the health of our kids and our spouses should be paramount. The EPA also has good information on indoor air monitors.

Another benefit of the Govee is that it pushes a message to your phone, wherever you are, when PM spikes.  At 6:40, just as I was lighting the pellet stove, it briefly spiked to 35 ug/m3, and I got a message on the cellphone when I looked at it, 15 minutes later, at 7:05.  The average on Feb. 21^st was 3 ug/M3.and there was also a little PM elevation around dinner.

 

Low-cost sensors are also useful for neighbors who may be breathing wood smoke from someone else’s wood stove.  When outdoor air quality is bad, it leaks into homes and these sensors can help neighbors talk to each other using data, not emotional reactions, to wood smoke issues.

 

Data from my home’s pellet stove

 

My pellet stove emits a little smoke on start up, but I found that after the first half hour, there is no air quality impact that the sensors could detect. I turn my pellet stove off when we go to bed and when we wake up the sensors usually say the house has 1 µg/m³, meaning 1 microgram per cubic meter of air. By the time the pellets catch fire, it usually reads 6 or 7 ug/m3 but it can also go up to 30 or 40. But if we fry something for dinner, the sensor often goes to 30 or 40, and if we over fry something to the extent you can smell something is nearly burning, the sensor can read 100 or even 200. Our conclusion is that the riskiest behavior in the house is cooking, but your house may be very different, and a wood stove may emit far more indoor smoke than my pellet stove.

 

If I don’t clean the burn pot of my pellet stove, it takes longer for the pellets to light off, and there can be quite a bit of smoke. Currently, I have a Harman Accentra but I had the same problem with a Ravelli.  It appears that the exhaust fan doesn’t go on until the stove sensors fire in the burn pot, but by then the smoke has found any available crack to leak into the room.  This seems like a design flaw, but we all know that positive pressure in a firebox is a recipe for problems.  

 

In our house, we use an older gas stove that is located in the kitchen, about 15 feet away from the PM sensors which were placed just 2 feet away from the pellet stove. Our impression is that regardless of whether you have a gas, electric or induction stove, frying will reduce air quality, particularly at higher temperatures.  We don’t have a exhaust hood or fan above our cook stove, which we presume would be a big help to reduce PM from cooking. A hood with a fan exhausting to the outside may be the best investment in homes that fry food often.

 

Indoor air quality for wood stoves, pellet stoves and fireplaces

Conventional wisdom, based on tens of thousands of wood and pellet stove users, is that indoor smoke is usually far worse with wood stoves.  Part of the problem is that wood stoves need to be reloaded, usually every 1 – 4 hours, and depending on wind conditions outside, how quickly the door is opened, etc. the negative pressure in the firebox is broken, and smoke spills into the room. When a pellet stove is reloaded, you open a door to the hopper, not to the firebox, so there is no impact on pressure in the firebox and no opportunity for smoke leakage. Also, since the exhaust flue is powered by a fan in a much smaller pipe, windy conditions outside are far less likely to impact indoor air quality.

 

An air quality sensor can tell you how bad your indoor air gets when you reload – and crucially – how long it takes to get back to normal. Once you start measuring it, it gives you a metric which can lead to behavior change.

 

With both wood and pellet stoves, improper installation can aggravate or cause leakage of smoke. With pellet stoves, the exhaust pipe has positive pressure and can leak if it's not sealed or installed properly.  With wood stoves, a short exhaust pipe which can often be found in trailers, and self-installed stoves, can lack the suction needed to keep smoke from spilling out into the room.

 

Did I need the sensor to help me understand the relationship between cleaning my firepot better and start-up smoke?  Not necessarily, but it gave me data to measure it on a daily basis, better understanding the solution, and it gave my whole family some reassurance that the stove did not cause much of a problem at all compared to cooking. 

 

How much smoke is acceptable?

It is easy to say that no additional indoor PM is acceptable yet we all live with it when we cook, toast bread and vacuum floors and rugs.  The EPA and the World Health Organization(WHO) say that indoor 24-hour averages should be below 12 – 15 ug/m3, or more recently down to 9 ug/m3. My house, with cooking meals for 3 people and running a pellet stove from 6:30 AM to 10 PM, almost always stayed well under those average limits. However, in homes were a wood stove were to result in daily averages of 20 or more, that would likely be unacceptable to many people, as I think it should be.  Learning when and how to reload your stove quickly and efficiently may help.

 

In terms of outdoor, ambient wood smoke, we know that concentrations of wood stoves in valleys, especially those with more frequent and severe inversions can pose serious health risks.  I have come to believe that restrictions on the new installation of cord wood stoves in those areas is often a step in the right direction.  Wood stoves are not a good energy solution in any densely populated area, not because they are usually not operated well-enough with dry enough fuel. However, we think pellet stoves can be a far greater energy solution than they are today, and should be allowed to be installed even in areas where cord wood stoves aren’t.

 

The toughest question is how to compare and contrast the additional local PM from wood or pellet stoves and the disastrous global impact that oil and gas heating have.  All renewables are increasingly getting local pushback even in the face of overwhelming data showing we need to ramp up renewables far faster than we have been.

 

What do the academic studies say?

There have been multiple academic studies of indoor PM impact of cord wood stoves but we could not find any about pellet stoves. For wood stoves,  one study found an average of 20% higher PM in homes with wood stoves. Another said that wood stoves triple the PM in a homes. Another found that the age of the wood stove was not a determinant of indoor air pollution but more frequent cleaning of the flue was a factor. This was the same conclusion of a well-known study in British Columbia that found there was not a consistent relationship between stove technology and outdoor or indoor concentrations of PM_2.5. Yet another studyfound higher PM in homes with wood stoves and the primary mechanism for introducing PM into the home was opening the door to the stove.

 

Do air purifiers work for wood smoke?

Yes, air purifiers can be effective for indoor smoke from forest fires, your neighbor’s wood stove, or your own wood stove. AGH began promoting the use of air purifiers in 2015 and since then, the rise of wildfire smoke have made them a commonplace solution.  But if the problem is your own wood stove, you should fix the problem before putting a band-aid on the symptom of the problem.  One of the highest rated air purifiers is  Blueair Blue Pure 211i Max(around $279) or Blueair Blue Pure 211+ (around $169).  Both consistently perform nearly as well or better than more expensive ones. One downside for all air purifiers is the cost of replacement filters ($25 - $35 for Blueair filters) which should be replaced once or twice a year depending on how much you use it and how dirty your air is.

 

Purple Air Sensors

I have used multiple Purple Air sensors extensively but did not include any of the data here in part because they are far more complicated to set up and can be glitchy. They are highly recommended, however, for a wide variety of ambient PM measuring. Data from ours led us to the same conclusion: the pellet stove caused a spike in PM when it started, but air quality returned to the same levels as when the stove was off pretty quickly.  With the Purple Air, we also confirmed that by far the worst events in the house were cooking, not starting or operating the pellet stove. 

In 2019, I set up both indoor and outdoor Purple Air sensors at my house, and my neighbors’ who had a cord wood stove. Sensors with a circle around them are indoor. The data was made public, and of interest to the Purple Air community. 

 

Here the Purple Air sensor at the bottom, mostly in green was indoor and the upper one, mostly in yellow was outdoor. Thus, the 7 PM spike from cooking did not impact outdoor PM, but the stove lighting around 8 AM caused a spike indoor and outdoor. (This is data from 2 units but each unit is a combination of two sensors, and you can see how closely they track each other.) 

 

Use of Govee and Amazon sensors outdoors

The Govee and Amazon sensors are indoor sensors but I was curious to see if they could detect start up smoke of my pellet stove when placed on my front porch, about 25 feet and around a corner from my pellet stove exhaust pipe.  I brought both sensors outside and turned my stove off at 11 AM and turned back on at 4 PM.  The result indicates that outdoor emissions of this pellet stove start-up were not detectable at 25 feet away on a relatively windless day

 

This shows that both the Amazon and Govee monitors did not detect elevated PM2.5 during a pellet stove start-up cycle a 4:00 on Feb. 21 when placed about 25 feet from the pellet stove exhaust pipe. If the sensors were placed directly under the exhaust pipe, the results would be very different, as there is always a strong smell of smoke there.

 

Conclusion

We found that our pellet stove does not significantly impact air quality in our home compared to other daily activities such as cooking and cleaning.  The pellet stove does emit some PM on start-up, but on a daily or hourly average basis, it was usually still well within EPA and WHO recommended limits.

 

If you regularly smell wood smoke in your home, you have a problem and you should not delay in trying to fix it.  A low-cost air sensor can be an excellent way to assess the problem with reliable data, or let you know that you don’t really have much of a problem at all compared to other daily household events like cooking and cleaning. 

If you have a pellet stove that emits some smoke on start-up, or if you have done any air quality monitoring in your house with a wood or pellet stove, please contact us and share you experience.