When cleaner burning woodstove technology first emerged in the mid-80's, the EPA announced a four-year, two-phase plan to incorporate this technology into every new woodstove to be sold in the US.
The regulations pertaining to woodstove exhaust are very similar to those that apply to automobile exhaust. Older technology cars may remain on the road and old technology woodstoves may remain on the flue, but any new car or woodstove sold must comply with current emissions standards. As the old-technology cars and woodstoves die off and are replaced with new-technology models, air quality is automatically improved.
Here's a brief history of EPA woodstove emissions legislation:
1970's: Spiraling fuel prices cause consumers to turn to airtight woodstoves as an economical heating alternative. A typical airtight woodstove of this vintage emits 40-60 grams of particulates into the airshed every hour, and airborne wood smoke particulates become a problem, especially in rural areas where woodburning is prevalent.
Early 1980's: State and Federal EPA offices set up air testing stations to study woodstove particulates. Several States pass legislation limiting woodstove emissions: some areas institute "burn bans", which limit or prohibit woodstove use during periods of high airborne particulate pollution.
Mid 1980's: Motivated by existing and pending emissions regulations, woodstove Manufacturers
develop and introduce new, "clean air" reburn designs which dramatically reduce particulate woodstove emissions. There are two designs that prove effective:
Catalytic woodstove designs reburn the exhaust gases by causing the exhaust gases to come into contact with a catalytic converter element, similar to those used in automobiles.
Non-catalytic woodstove designs cause the exhaust gases to reburn in a secondary burn chamber located at the top of the firebox.
The public shies away from these newfangled critters, which are a little more complicated and slightly more expensive than the older, more familiar high emissions designs. The EPA decides that a slight nudge will be needed to speed up implementation of the new technology, and legislation is drafted regulating wood-burning heater emissions on a national level. Because catalytic converters become less effective over their 3-5 year lifespans, it is decided to hold new catalytic-equipped woodstoves to a lower emissions standard.
Wood furnaces, site-built masonry fireplaces and wood cookstoves are exempted from Federal EPA emissions requirements (a complete list of exempted appliances can be viewed on the EPA's website).
July 1, 1988: The EPA's Phase I regulations go into effect. All woodstoves manufactured after this date must emit fewer than 8.5 grams of particulates per hour (5.5 grams/hr if catalytic equipped), and are to be exempted from local "burn bans". Existing inventories of non-approved woodstoves may continue to be sold intil 1990.
July 1, 1990: All woodstoves sold at retail after this date must comply with Phase I emissions regulations.
July 1, 1990: Phase II regulations go into effect. All woodstoves manufactured after this date must comply with Phase II limits of 7.5 grams/hr (4.1 grams/hr if catalytic equipped). Existing inventories of Phase I approved woodstoves may continue to be sold intil 1992.
July 1, 1992: All woodstoves sold at retail after this date must comply with Phase II emissions regulations.
1992-2000: EPA approved woodstove owners report a dramatic decrease in fuel usage. Chimney Sweeps notice a tremendous decrease in creosote formation in flues venting EPA approved stoves. As the number of homes being heated with "clean air" woodstoves increases, areas that had experienced numerous "burn ban" episodes each Winter due to wood smoke pollution back in the 1980's report no such incident days whatsoever.
July 1, 2000: Latest Revision of the Clean Air Act: in the spirit of "If it ain't broke, don't fix it", Phase II woodstove emissions standards remain unchanged.
2006: The EPA's program to cause a gradual changeout of the old 40-60 gram "smoke dragons" for the new, environmentally friendly models has been an unqualified success: the EPA estimates that these higher efficiency woodstoves save the nation $29 million annually by reducing wood use and the need for chimney cleanings.
The Future: EPA air quality studies continue, and woodstove design engineers just can't seem to stop tweaking their reburn designs, so it is possible the EPA will introduce even stricter woodstove emissions regulations, perhaps modeled after Washington State's limit of 4.5 grams/hr (2.5 grams if catalytic equipped).