Article source: www.woodheat.org

Advanced Wood Burners Cut the Smoke

The new wood burning technology found in EPA certified stoves goes a long way toward solving all three wood smoke problems: airshed contamination, nuisance wood smoke and indoor air pollution. These advanced stoves, inserts, fireplaces and furnaces cut wood smoke by up to ninety percent compared to older so-called ‘airtight’ stoves, and also spill less smoke into the indoor air because fires don’t tend to smoulder in them, the condition that most contributes to smoky indoor air.

Smoke emissions from older conventional wood stoves average at least 25 grams per hour of operation, while the emissions from older wood-fired outdoor boilers range from 50 g/h to well over 100 g/h. In contrast, the EPA regulation limits emissions of certified wood stoves to no more than 7.5 g/h. However, since the regulation was first established in 1988, the average emissions of certified stoves have declined steadily due to advances in technology and competition among manufacturers. Today, most current wood stove models emit only 2 to 4 g/h.

Although the EPA emissions limits are stated as solid particles (particulates) collected on filters, other detailed testing has shown that the emission of the scary-sounding polycyclic aromatic hydrocarbons like fluorene and benzo (a) pyrene, as well as volatile organic compounds like benzene and xylene are all far lower in the exhaust from advanced wood heating equipment than from old style wood burners.

Despite what some anti-wood heating activists have claimed, the technology is effective in reducing pollution. The reduction in smoke emissions has been a significant technological breakthrough in wood burning and is noticeable at the top of the chimney where no visible smoke is seen.

Advanced equipment is more efficient too

Just as noticeable to users, however, is the increase in efficiency that results from burning and not wasting the energy-rich smoke. Conventional wood stoves range in efficiency from a low of about 35 percent for a cast iron box stove or furnace to a high of as much as 55 percent for a 1970s era ‘airtight’. Most older outdoor boilers are less than 50% efficient. In contrast, EPA certified wood stoves average around 70 percent and none are less than 60 percent efficient. The new breed of emissions certified outdoor boilers are also much more efficient.

The difference in efficiency between conventional wood burning equipment and the advanced low-emission models is so significant that users can immediately see the difference when they upgrade and begin using a new stove. The reduction in fuelwood consumption by up to one-third is significant for each household that uses the new technology, but it also has the potential to increase the number of houses that can be heated based on the sustainable harvesting of a given area of forested land. Another significant factor that reduces a wood-heated household’s impact on the forest resource is the lower heat energy requirements of modern housing. Together, the increase in wood burning appliance efficiency and improvements in housing energy conservation can roughly double the number of dwellings that can be heated by the yield from a given woodlot compared to just 25 years ago.

An outdoor boiler firing up.Community-wide smoke problems are uncommon in areas where level topography does not produce the same number or severity of winter inversions that trap smoke close to the ground. While community level smoke problems are relatively rare, nuisance smoke caused by thoughtless neighbours has been identified as a problem in dozens of towns. One technology in particular has been the focus of many complaints. Outdoor wood-fired boilers (OWB), which look like metal garden sheds and send hot water to one or more buildings through buried pipes, have become notorious for the dense smoke they produce. Small towns have enacted bylaws restricting the installation of outdoor boilers by either banning them from residential areas or placing limits on their proximity to property lines.

The source of the problem is that central heating furnaces and boilers, including OWBs, were exempt from the original EPA emission rules back in 1988 on the basis that there were too few of them to bother regulating. Well, that was then. Now OWBs are very popular and as a result a new smoke emissions test for OWBs has been approved and certified models are now on the market. On paper the new breed of OWBs look much better than the older, smokier versions. Time will tell if they are clean burning enough to satisfy regulators and reduce public complaints.