Blog Post

Have Your Wood or Pellet Stove and Cleaner Air Too

Wood smoke is still a guilty pleasure in the northern U.S. and Canada. But newer wood stove technologies produce less smoke—and less guilt.

This gravity-fed pellet stove from Wiseway produces few emissions and uses no electricity.Photo Credit: Wiseway Pellet Stoves

I love fall and the start of heating season here in Vermont: the leaves are changing colors, there’s frost on the grass, and the morning fog mingles with smoke from wood stoves, its scent triggering memories of home, family, warmth, and the pending winter.

There must be some primeval connection to smoke that I find comforting, yet I know that wood smoke is also a significant source of pollution in the form of fine particulates that are lung irritants and asthmagens; sulfur oxides and nitrogen oxides that cause acid rain; and polycyclic aromatic hydrocarbons (PAHs), benzene, formaldehyde, and dioxin that are carcinogenic. Fortunately, there are a number of newer wood stoves available that significantly reduce these emissions.

Wood can be sustainable—or not

For wood to be an environmentally viable fuel requires careful application—sizing stoves appropriately, using properly sized and dried wood, and operating stoves correctly—and you need an efficient wood-burning appliance.

Older wood stoves can have particulate emission rates of 30 or more grams per hour (g/hr), and many of these are still in use today.

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For perspective, gas and oil furnaces have emission rates of about 0.001 and 0.02 g/hr, respectively.

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In 1988, the EPA began limiting particulate emissions from wood stoves to 7.5 g/hr for non-catalytic and 4.1 g/hr for catalytic wood stoves, and the State of Washington tightened emission standards further, establishing 4.5 and 2.4 g/hr standards for these respective stoves. But wood stove technology has surpassed these regulations, and many stoves are now available with emission rates below 1.0 g/hr.

Just say no to smoldering

Gone are the days of placing logs in a chamber and dampening the fire to smolder for hours, releasing a little heat into the room and a big cloud of particulates into the atmosphere. Today’s stoves use either two combustion chambers that create intense heat and fully burn the wood; or they burn at a lower temperature and use catalytic converters to eliminate most particulates and transform combustion gases into water and CO2.

Both technologies have their pros and cons which have spurned years of “cat” versus “non-cat” debates: catalytic models create fewer emissions but require platinum or palladium converters that need to be replaced over time; and non-catalytic units are relatively simple to operate but are not quite as efficient.

Getting high-tech with pellet stoves

A third option, the pellet stove, burns compressed wood pellets and is known for low emissions (many release less than 1.0 g/hr). These typically require electricity to power controls and fans that improve combustion, turn augers to deliver pellets, and circulate the heat. The most efficient models, listed in GreenSpec, use electronically commutated motors and some come with battery backup options for use during power outages.

A pellet stove’s use of electricity and noise from the blower motor can be detractions, but there is now an alternative: one company listed in GreenSpec now offers a pellet stove that requires no electricity. The pellets are gravity fed and burn using two-stage combustion. The emissions from these power-free stoves are higher (1.9 g/hr) than those of the most efficient competitors, and they look a little funky, but they are quiet—and the company can even integrate a water-heating feature.

Getting cleaner burns from logs

There are a few wood stoves available that release less than 1.5 g/hr, including hybrid models as well as a few catalytic and non-catalytic stoves. The hybrid stoves combine catalytic and two-stage combustion, creating the lowest emissions of any wood stove and better than many pellet stoves.

 According to Rod Tinnemore, environmental specialist, who oversees Washington’s woodstove program, “Hybrid stoves work well at both low and high burn rates.” By combining technologies, some hybrid stoves now have emission rates below 0.5 g/hr. And though the EPA’s emissions ratings only account for particulates, “the catalytic converter will reduce carbon monoxide and PAHs as well,” said Tinnemore.

The performance of these wood stoves is impressive, yet the technology is still in its infancy, according to Tinnemore. Wood may never be as clean a fuel as natural gas, but using the new generation of wood and pellet stoves will help us reduce our dependence on fossil fuels and lower heating bills substantially, and maybe I can enjoy the smoke with a little less guilt.

Published October 3, 2012

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Comments

May 17, 2013 - 7:00 pm

I am a little (a lot) late to this conversation, but I think the only wood-burning appliances should be direct vent masonry ovens which burn at such high temperatures that they burn off all the nasty particulates and gases.  And even then, they should only be used in an emergency situation, where power is out for an extended period of time.

Wood burning in my area (near Fresno, CA) destroyed my health and made me chemically hypersensitive.  Not just residential wood burning, but also the nasty, dirty practice of agricultural waste burning.

Combustion appliances are really not in tune with the high-performance standards I think that Building Green would want for all homes, especially new homes.  A truly healthy home would not have any, in my opinion, except perhaps a masonry oven for emergencies only.

October 5, 2012 - 8:23 am

I did a quick Google search and found several comparisions of heating sources but few showed pollution in the assessment.  Here's one from the EU. Good luck reading it.

http://acm.eionet.europa.eu/reports/docs/ETCACC_TP_2009_18_LCA_GHG_AE_2013-2030.pdf 

October 4, 2012 - 4:35 pm

Hi Cate,

I am not aware of a thorough life cycle assessment that compares wood against other fuel options across the board. The best thing we can do is make sure our homes are well-insulated so we can use as little fuel as possible. Wood may not be the best fuel choice in that scenario, but wood can be an important piece of our overall energy puzzle, providing some protection against power outages and future fuel disruptions.

Burning wood for fuel is a complex issue and its environmental impact/appropriateness depends on a number of factors (where you live, building envelope/ventilation, geography/thermal inversions, etc). But I think we are seeing the beginning of some real technology breakthroughs in terms of wood stove performance, and the combination of lower emissions and the possibility of using pellets made from beetle kill wood just might make wood a viable choice in more parts of the country.

Brent