Mapping wood heating and wood smoke in the United States

Updated, Dec., 2020: Wood heating has made a comeback in the United States and has been the fastest growing heating fuel for most years between 2005 and 2015, according to US Census figures. Currently, 2.36 million homes in the United States use wood as a primary heating fuel (ACS, 2015, 1-year estimates). And 8.8 U.S. million homes use it as a secondary heating fuel (EIA, RECS, 2009). Wood was the dominant residential heating fuel in the United states until coal began to take over in the 1880s. After that, heating oil and then gas became popular. The percent of the population primarily heating with wood dropped from 23% in the 1940s, when the US Census first began tracking heat, to a low point of 1.3% in 1970, when fossil fuels were cheap and popular.

Wood smoke follows wood heater installations and the first map shows shows county level particulate matter from residential wood combustion based on the 2011 National Emissions Inventory, Version 1.5.  The EPA should be releasing data from the 2014 National Emissions Inventory this year, so that residential wood smoke changes can be compared from 2011 to 2014.  Emissions from fireplaces - and more recently from outdoor fire pits - mix with smoke from residential wood heaters, and complicate assessing the impact of wood stoves and boilers.

This second map also shows PM 2.5 emissions from residential wood combustion by county, but its on a per capita basis according to the 2008 National Emissions Inventory, in this  EPA report, "New Methodology for Estimating Emissions from Residential Wood Combustion." It appears to show the densest per capita concentrations of PM2.5 in Wisconsin and Minnesota where the most outdoor wood boilers are made and installed.

The third map, from the same 2008 EPA, report provides further detail on the source of PM 2.5 emissions by appliance type. Each appliance type is represented by a different color. Red represents fireplaces, green represents fireplaces with inserts, dark blue represents woodstoves, light blue represents indoor furnaces, magenta represents outdoor hydronic heaters, and yellow represents wax/sawdust firelogs. While the terminology is somewhat confusing, the map shows some interesting trends.  For instance, wood stoves emit the majority of PM in the Northeast, while outdoor hydronic heaters are the largest source in the Great Lake states (outdoor wood boilers continued their popularity in these states after the 2008 EPA report). Fireplaces with inserts are the largest emitter in most of the south and California. Indoor furnaces are the most common source of PM pollution in Ohio, Indiana, and Illinois.

The next map was produced by the Census Bureau, showing per capita use of wood stoves. It shows 17.8% of homes in Vermont use wood or pellets as a primary heat source in 2012. Maine had the second highest percentage at 13.7% of homes. Out West, Montana has the highest percentage with 9.2% of homes, followed by Idaho at 7.9% and Oregon at 7.1%. On the US mainland, the states with the least wood heating are predictably Florida, at 0.2% of the population and then Texas at 0.4%.

The Alliance for Green Heat produced a map using Census data to show the continued growth of wood heating between 2000 and 2012. By 2010, the growth trend was well established, due in part to the housing crisis and recession. In that period, wood heat doubled in about 10 states, mostly in the Northeast.

This map below, made the Alliance for Green Heat, also uses Census data but breaks down primary wood heating households by Congressional districts. This provides a much more detailed look at the geography of wood heating compared to state level details. Presumably, a map showing wood usage at the county level could also be produced.  

This last map shows a curious phenomenon in 1950 where the Census Bureau found higher rates of primary wood heating in southern states than in many northern ones. This is likely due to the quicker penetration of fossil fuels in northern states, whereas room heaters in southern states, including those in many poor, rural black and white households, continued to operate on cordwood.

This map shows a per capita use of primary wood heat in impoverished counties.  Note the hot spots in northern Maine, West Virginia, Arkansas and the Navajo reservation in New Mexico.  We are unclear if Native American populations are among the hot spots in Washington, Oregon, and Northern California.

This final map of oil and gas heating use per capita generally correlates with heating costs, or at least it did before gas and oil prices plunged in 2019 - 2020.  Where there is high use of oil and gas, there is generally high use of wood heat in rural areas.

What Consumers Need to Know about New EPA Wood Stove Rules

Updated: May 2022

There have been many claims, counter-claims, predictions and fears about the new EPA regulations on wood and pellet heaters.  Here is a summary of the key points in the rule that will impact you, the consumer.

The rule became law on Friday, May 15, 2015 and various provisions go into effect on Jan. 1, 2016, May 15, 2016 and May 15, 2020.  On March 11, 2020 the EPA ruled that no major changes would be made to the rule and that there would not be any retailer "sell-through" period. Scroll to the bottom to see a timeline of implementation. This rule is an NSPS - a New Source Performance Standard  - established by the EPA with input from industry, states, consumers and other stakeholders.

Wood stoves: Most stove consumers will not notice any differences between stoves sold before 2015 and those sold now. As of 2016, stoves must not emit more than 4.5 grams an hour of particulates and after May 15, 2020, 2  or 2.5 grams an hour.  One of the biggest changes is that some of the really cheap, uncertified wood stoves went off the market after Jan. 1, 2016.  Similar, certified stoves that are EPA certified and put out less smoke are still available for $500 - $900.  Consumers will see more hybrid and catalytic models.

Pellet stoves: Consumers will also not notice differences in pellet stoves either but pellet stoves are getting gradually cleaner and more efficient.  As of Jan. 1, 2016 all pellet stoves have to be certified by the EPA.  Many models are also getting more efficient.  In 2020, pellet stoves also have to emit no more than 2 grams an hour. As of Nov.  2020, seventeen models are more than 80% efficient and more than half only emit 1 gram or less of particulate matter. Just because a stove is higher efficiency does not mean its more durable.

Prices: Prices are expected to rise modestly. As of November 2020, tariffs on steel were the biggest driving factor, not EPA regulations.  In 2018, we analyzed 77 popular models and found a 3-4% price rise since May 2015, but that may be due to a host of factors, and not necessarily impact of regulations. In the longer term some manufacturers say their stove prices may go up $75 - $400 by 2020.  

Retail “sell-through” period: Retailers had until Dec. 31, 2015 to sell existing stock, after the law went into effect on May 15, 2015.  There is not a similar sell-through provision in 2020 and all stoves that are not 2020 compliant need to be sold by May 15.  

Existing and second hand stoves: Existing stoves are not impacted by these rules, nor is the vibrant second hand market for wood stoves. States can regulate existing and uncertified stoves and two states - Washington and Oregon - do not allow anyone to sell or install an uncertified stove off the second hand market.  All states allow consumers to purchase and install second hand EPA certified stoves. (How to buy a second-hand EPA certified stove.)

Corn, coal and multi-fuel stoves: Corn and coal only stoves are not covered by EPA rules and can continue to be sold without any government emission regulation, so long as they don't advertise that they can also use wood or pellets. To advertise a multi-fuel stove that can use pellets and corn, the stove has to be certified for pellets and also tested with corn.  There is no threshold for emissions with corn, but the stove has to also be tested with corn and that data must be submitted to the EPA.  (More on corn stoves and coal stoves.)

Misleading advertising: Some manufacturers post unverified and exaggerated efficiency claims on their brochures and websites but this is gradually improving.  The new rules specify how stove efficiency is to be tested and reported to the EPA, and now all models have verified efficiencies on the list of EPA certified stoves. To date, neither the EPA nor state agencies have cracked down on exaggerated and misleading efficiency claims in advertisements.  As of 2021, consumers can rely on most certificates issued by manufactures about whether a stove model qualifies for the 26% federal tax credit.

Efficiency: There is no minimum efficiency standard, but the new rule requires efficiency testing and reporting.  Prior to 2015, manufacturers were allowed to keep their efficiencies confidential and most did not disclose them.  The average wood and pellet stove was about 70% efficient, but has been going up.  The median pellet stove efficiency is steadily climbing and is now about 74%, with some in the mid and high 80s.

New hangtags: The EPA has been issuing special, voluntary hang tags for those stoves and boilers that already meet the stricter Step 2 standards (2 grams and hour), disclose their actual efficiency and/or that have been designed and tested with cord wood. This will help consumers more easily identify the cleaner stoves and those that are designed to be used with cordwood - the same type of fuel that consumers use.  (Update: as of summer of 2017, a technical testing problem led to a temporary recall of these hang tags.) As of May 2020, only stoves tested and certified with cord wood will be allowed to use the hang-tag.

Carbon monoxide (CO): The new rules do not limit the amount of CO that can be emitted but require that it be tested and reported. There is a much wider range of CO than there is PM, with many pellet stoves under .05 grams per minute, and many non-catalytic wood stoves higher than 1.0 grams per minute, a 20-fold difference.

Stoves tested with cordwood: The rules set up an alternative, voluntary compliance option for Step 2 emission levels as of 2020 of 2.5 grams an hour for stoves tested with the ASTM cord wood

method.  There was a hope that these stoves would burn cleaner in hands of consumers, but that has not turned out to be the case. Generally, the cord wood test is a bit easier and manufacturers prefer to use it and tend to get cleaner PM numbers in the lab. No matter how the stove was tested in the lab, it is essential to use dry wood and give the stove enough air to get good performance and minimize health issues from wood smoke.

Pellet fuel: All new pellet stoves must be tested and warrantied to use with pellets that are certified by a third party entity - either the Pellet Fuels Institute (PFI), ENplus or CANplus. Consumers will likely see more and more pellets certified by one of those entities, which means they meet certain quality and consistency standards. As of 2020, 34 pellet plants make PFI certified pellets.  AGH urges consumers to purchase third party certified fuel, which in the U.S. means PFI certified.

Export stoves: US manufacturers can continue to make and sell their existing stoves that do not meet the new EPA standards in other countries.  Uncertified stoves with no emission controls or testing can be sold in most of the world.  US stove companies are also increasingly exporting to countries that have emission standards, like Japan, Korea, Australia and New Zealand. These stoves have to be labeled as an “export stove. May not be sold or operated within the United States.” 

Masonry Heaters: The EPA did not set emission standards for masonry heaters in this rule, but asked the Masonry Heater Association to further develop a testing standard so that they could be included in the next NSPS, which should be in 2023.

Fireplaces: The new rules do not apply to fireplaces, but there is a voluntary method for cleaner fireplaces to be tested and qualified by the EPA.  This rule does not refer to the voluntary program, which may mean there is little interest in including fireplaces in the next NSPS.

Owners manuals: All owners manuals should be updated as of May 15, 2015. Updated manuals will have more detail and must instruct operators how to get optimal performance from the stove or boiler.

Litigation: The largest stove and boiler industry association, the HPBA filed suit over the 2020 emission standards for boilers and the case was delayed many times.  Air quality groups are joining that suit to defend it from being weakened or delayed.  In August of 2021 the Federal Appeals Court ruled in favor of EPA, and dismissed industry's challenge.

Role of states: Several states have passed resolutions barring state agencies from enforcing this NSPS but the rule clearly states that it does “not impose any requirements on state and local governments.”   To date, Missouri, Michigan and Virginia have passed laws barring state enforcement, largely a symbolic gesture. A number of other states, including New Hamphsire and Vermont have formally taken delegation of NSPS provisions to achieve cleaner air in their states and protect consumers.

Boilers & Furnaces

Boilers: Like stoves, boilers must meet Step 1 emission limits by May 15.  Retailers could still sell older, uncertified and unqualified boilers through Dec. 31, 2015.  In 2020, they must meet stricter emission limits.  EPA regulations have led to far more efficient boilers, with many now topping 80% but the regulations have hit the boiler and furnace industry harder than the stove industry.  Only 29 of the more than 100 boiler and furnace models are now 2020 compliant.

Warm air furnaces: Furnaces that heat air, instead of water, got a reprieve from the EPA after intensive advocacy by industry and pressure from Congress.  Small ones have to meet Step 1 emission standards by May 15, 2016 and large ones not until May 15, 2017. Only 3 furnace models are now 2020 compliant.

Loophole for unregulated outdoor boilers: Manufacturers of unregulated outdoor wood boilers can continue to make and sell these units for "commercial" applications.  However, one outdoor boiler company has already indicated that as long as the customer assures the dealer that the unit will be used for commercial purposes, its up to the consumer to use it as they please.

Boiler and furnace prices: Unlike stoves, options for consumers will change more, since the boiler furnace industry had not been regulated and many low-cost, low-efficiency units were on the market.  Prices - and efficiencies- are likely to rise significantly but operating costs will be significantly lower.

Moisture meters: Conventional uncertified forced air furnaces and then certified ones must come with a free moisture meter.  (Some advocates had urged all stoves to come with moisture meters.)

Comments? If you think we have omitted important information in the NSPS for consumers, please let us know at  info@forgreenheat.org.

For more info:

• The EPA's BurnWise website
• Position of the main industry association, the HPBA
• EPA Rules Begin Cleaner Chapter for Wood Heating
• Air Quality Groups Intervene in Industry Lawsuit Against EPA
• Talks Yield Some Consensus Between Industry, Enviro Groups
• Independent Stove Manufacture Challenges Stove Industry Positions on NSPS 

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.