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.

New EPA Stove Regulations Begin Cleaner Chapter for Wood Heating

Statement by the Alliance for Green Heat on the Wood Heater NSPS

Key EPA architects of this NSPS include
Greg Green, left, and Gil Wood,  right  and
Amanda Simcox. Gil retired on February 3. 

Overall, the EPA did a good job and released a fair rule that includes many compromises between industry and air quality agencies.  We think these rules are good for consumers and will not drive prices up substantially for most product categories, but will result in cleaner and more efficient appliances that will ultimately save consumers time and money. This is our initial reaction to the rule, which we will be followed by a more thorough analysis.

High performance stoves: The EPA took some key steps to address the lack of recognition for high performing appliances. Notably, stoves that test with cordwood in the next 5 years can use a special EPA label that will alert consumers that the device is designed and tested for use like the consumer will use it. This shift is possibly as important than just lowering emission standards for wood stoves. Along these lines, the EPA is also allowing stoves that already meet the 2020 standards, to use a special label so consumers can more easily recognize these higher performing stoves. We are, however, very disappointed that the EPA removed the long-standing requirement that all stoves have a consumer hang-tag that helps consumers better appreciate the basic differences between all stoves on the showroom floor.

Boiler testing: Another positive step forward is EPA’s recognition of the European test method EN303-5 to certify European style indoor pellet boilers that have been accepted by Renewable Heat New York (RHNY). Also boilers certified by the New York State Department of Environmental Conservation (NYSDEC) will be automatically deemed EPA certified. This is another step to recognizing higher performance equipment. NYSERDA deserves credit for the R&D, test method and other funding that EPA and DOE should have been doing to develop higher performance equipment. These parts of the new EPA rule will help give consumers more options to buy cleaner and more efficient devices.

Stove emission standards: As expected, the EPA is staying with the de facto status quo for the next 5 years, at 4.5 grams an hour (g/hr). The 2 g/hr standard for stoves as of 2020 is fair and reasonable. As the EPA explained in the rule “nearly 90 percent of current catalytic/hybrid stoves and over 18 percent of current non-catalytic stoves” already meet the Step 2 emission limit of 2 g/hr. We hope that those manufacturers who have to redesign stoves use the opportunity to redesign to use cordwood and to reduce start-up and fugitive emissions. The optional Step 2 certification test for cordwood at 2.5 g/hr represents a very creative and positive approach by the EPA to move towards required cord wood testing.

Some independent stove and boiler companies played a vital role in broadening the debate and sharing key data sets that enabled the EPA to show that some stoves can already meet the Step 2 standards of 2 g/hr with cordwood. We are pleased that companies who participated in the 2013 Wood Stove Design Challenge helped the EPA and OMB understand that smallest manufacturers can undertake the R&D to make very clean and affordable stoves that operate well on cordwood.

Key issues not addressed: Some of the most important issues with wood stoves are difficult to address in regulations, such as indoor air quality from fugitive smoke and the ability for homeowners to reduce air-flow so much that the stove smolders for hours on end, which is often a nightly occurrence. Ultimately, we believe that some types of automation are needed to prevent the widespread consumer misuse of wood stoves. The attempt by the EPA to set a maximum emission level while the stove is on its lowest burn rate was a good start. We had urged the EPA to more formally address alternative tests for automated stoves that hold tremendous promise to reduce widespread poor operation by consumers.

Warm air furnaces: Delaying the standards for all warm air furnaces for 1 - 2 years was a mistake because some companies have little ability or intention of meeting the Step 1 standards. An interim measure after 6 months to distinguish between companies on their way towards meeting standards and those who aren’t would have been far better.

Exempt wood stoves: We are very pleased to see that the era of exempt wood stoves is over. About 1 out of every 3 or 4 new wood stoves sold in America has been exempt in recent years and EPA had considered a weaker standard for them, but is now holding them to same standard as all other stoves.

Masonry heaters: The EPA was not able to set standards for masonry heaters but we are glad to see that the EPA has charted a path forward to work with the Masonry Heater Association so that masonry heaters become a certified appliance category

Sell-through period: The sell-through period, set at 8 months through December 31st is fair for certified wood stoves, pellet stoves and qualified or EN303-5 approved boilers, but too long for exempt wood stoves and traditional outdoor boilers which should have come off the market sooner.

Electronic reporting: We were very glad to see that the EPA will begin electronic reporting for stove certification tests and provide more transparency for the public and access more data that is not Confidential Business Information (CBI) about stove tests.

Efficiency: Achievable efficiency standards are important in the near future and we are pleased that the EPA will finally require the manufacturers to test for, and report actual efficiency numbers not only to the EPA, but also on their websites. In practice however, many existing stoves many not have to retest for 3-5 years and it is unclear if they will have to disclose efficiency before then, unless they do it voluntarily. This is particularly important for boilers and pellet stoves that have a very wide range of efficiencies.

Renewable energy: We are very disappointed that the EPA did not mention the term “renewable” in this rule. The EPA Office of Air and Radiation should take into consideration that this sector has potential not just to make cleaner energy, but to use a renewable energy source and displace fossil fuels. Governor Cuomo’s Renewable Heat New York is investing tens of millions into the sector and integrates the goal of driving down emissions, driving up efficiency while replacing fossil fuels and offering homeowners an affordable, renewable heating source. In addition to setting minimum emission standards for lab testing, the EPA should adopt a more integrated approach to this technology that is being increasingly adopted not just by New York, but by other states as well.

In conclusion, the EPA crafted a fair and balanced rule overall and took some important steps towards testing with cordwood and recognizing those companies who take steps to build stoves based on how consumers operates them. In the long run, this new rule will result in cleaner appliances and a better foundation for renewable wood and pellet heating.

Full EPA rule and fact sheets

Wood and pellet stoves

Step	New PM emissions limit	Compliance deadlines
Step 1: All uncertified wood and pellet stoves (cat and non-cat)	4.5 grams per hour for crib wood test method If tested with cordwood, emissions test method must be approved, and stoves must meet crib wood limit	60 days after publication in the Federal Register
Step 2: All wood and pellet stoves (cat and non-cat)	2.0 grams per hour, or 2.5 grams per hour if tested with cordwood (test method must be approved)	5 years after publication in the Federal Register (2020)

Hydronic heaters

Step	New PM emissions limit	Compliance deadlines
Step 1	0.32 pounds per million Btu heat output (weighted average), with a cap of 18 grams per hour for individual test runs (crib wood test method) If tested with cordwood, emissions test method must be approved, and stoves must meet crib wood limit	60 days after publication in the Federal Register
Step 2	0.10 pounds per million Btu heat output for each burn rate, or 0.15 pounds per million Btu heat output for each burn rate. If tested with cordwood; method must be approved	5 years after publication in the Federal Register (2020)

Warm air furnaces

Step	Standard	Compliance deadlines
Step 1	Operational/work practice standards	60 days after publication in the Federal Register
Step 2	Emissions limit of 0.93 pounds of PM per million Btu heat output, weighted average. Cordwood testing is required for forced air furnaces	Small furnaces: 1 year after publication in the Federal Register (2016) Large furnaces: 2 years after publication (2017)
Step 3	Emissions limit of 0.15 pounds of PM per million Btu heat output for each individual burn rate. Cordwood testing required	All furnaces: 5 years after publication in the Federal Register (2020)

Related stories:
Private Talks Yield Consensus on Key Issues in NSPS
Paper Undermines Stove Industry Variability Study

Wood Heating Trends in Utah

The proposal by the Governor of Utah to ban the wintertime use of wood and pellet stoves was met with intense opposition from a large majority of Utah residents and the wood stove industry. It also underscored the need for Utah state agencies, the media, and the public to better understand the role of wood heating and its prevalence in the United States. This short paper compares census data of wood heating in Utah compared to the rest of the country.

As of 2013, 10,500, or 1.2%, of Utah residents use mainly wood and pellets for their primary heating, far less than the national average of 2.1%, according to the US Census. There are likely to be an additional 40,000 to 50,000 who use it as a secondary heat source, though the US Census does not track secondary heating.  The EPA however estimates that there are about 93,000 wood and pellet stoves in Utah, some of which may not be used at all or only occasionally.

Utah is one of the states that buck the national norm, in that far more homes heated with wood and pellets in 1990 compared to 1940. Utah residents gave up wood heating faster than the United States as a whole, with the number of homes mainly heating with wood hitting a low point in 1950, two decades before the rest of the country. But between 1970 and 1990, Utahns embraced wood heating far more aggressively than the rest of the country. The number of Utah homes mainly heating with wood rose from 0.3% in 1970 to 3.2% in 1990, a high point that the state has not hit since then.


The rapid growth of wood and pellets in Utah since 1970 is likely due to many of the same reasons it has grown so quickly elsewhere: both gas and oil prices had been climbing, until gas prices finally dropped in 2008 and oil prices just starting dropping in 2014.  And, the increase of wood and pellet heating may also be linked to an increased desire for household energy security by both conservative and liberal households, but for different reasons.

Median household income remained relatively static in Utah for most of the 2000s before they began falling in 2008 and rising again in 2012, compared to the US where incomes first decreased in 2007 and only started recovering in 2013. Often, more households turn away wood heating as incomes rise and this is likely a factor in Utah since 2012 as well.

Since 2005, the percent of Utahns using wood or pellet as a primary or sole heat source has ranged between 1% and 1.4%, and since 2010 has remained steady at 1.2%, significantly below the national rate of 2.1% that has remained unchanged since 2009. Wood heating peaked in 2009, at the height of the recession and dropped slightly as the economy has picked up.

Wood and pellets are the fastest growing heating fuel in Utah, followed by electricity, as it is the US overall. Wood and pellet heating as a primary heat source had increased nearly 40% in Utah from 2000 to 2013, slightly less than the nation overall.

Utah is quite different than national heating trends when it comes to gas and oil. Gas heating has grown 30% in Utah since 2000, yet has only grown by 4% nationally. This increase in gas heating may be tied to slower growth of wood heating in areas with gas lines, while wood heating remains robust in areas without gas lines. Accurate county data could confirm this.  And oil heating has dropped far quicker in Utah than it has in the nation overall, although it has not been a very widespread form of residential heating in Utah.

Utah has the lowest percentage of homes heated primarily with wood in the West.  The Census does not have county level data of wood heating in Utah, but typically rural counties have far more wood heating than more urban ones.  And, lower income counties typically have more primary wood heating and higher income counties have more secondary wood heating.

EPA Estimates of Fireplaces, Stoves and Boilers in Utah

The EPA figures, above, estimate nearly a quarter million wood fueled devices in Utah.  A majority of those are fireplaces and studies show that a large percent of fireplaces are never used or only used once a week, unlike stoves which are often used every day.  About 93,000 units are stoves, nearly 16,000 of which are pellet stoves, 48,000 uncertified stoves (most made prior to 1990) and 26,000 are EPA certified stoves, made since 1990.

As this chart shows, 84% of Utah residents heat with gas, one of the highest percentages in the U.S. The second most popular heating fuel is electricity, which heats 11% of Utah homes, followed by propane, which heats 2%.  The fourth most common heating fuel is wood and pellets which account for 1.2% of homes.