Six states have 70% of all installed outdoor wood boilers: Michigan, Wisconsin, Minnesota, Ohio, New York, and Pennsylvania. Michigan alone is home to 20%!
In a March 2006 study, it was estimated that there were nearly 166,000 unregulated outdoor wood boilers (OWBs) in the U.S. As of then, nearly 20% of all OWBs were in Michigan, where many of the top manufacturers are located. Of the 6 states, none have yet to successfully regulate OWBs and allow only the cleaner burning, EPA qualified versions to be installed. New York legislators attempted to pass a bill to regulate use at the state level, but the bill is currently considered dead in the water. Still, the EPA considers the voluntary OWB program to be a success because it has led to the development of extremely clean burning units. Unfortunately, only a handful of states restrict installations to clean units. Pennsylvania is aiming to join their number with a set of regulations currently in progress.