top of page
OWB, Rt 7, Worcester NY, Oct. 2021 ja photo.jpg

Outdoor Boilers

Outdoor wood boilers, also known as hydronic heaters, caught on colder, rural areas where fuel is abundant, particularly in the Great Lake states where most of them are built. They began as a very basic, unregulated technology that was advertised as being an affordable and efficient way to heat your home. However, most were extremely inefficient and polluting. Their excessive pollution is one of the main drivers of the new 2015 EPA stove and boiler regulations.


Today’s outdoor wood boilers are regulated by the EPA and contain more sophisticated technology than units made and sold previously. Their attraction is that operators do not have to bring the wood into their homes and can use large pieces of wood. Many homeowners also use these boilers to heat their domestic hot water, which means they operate year-round at levels far below what they are designed for, adding to smoke problems. However, even the units that meet EPA requirements between 2015 and 2020 can be problematic in the hands of homeowners, some of whom are used to using unsplit green logs and even burning household garbage.

Axe in Tree Stump

Certified Outdoor Boilers:

Before establishing federal requirements for hydronic heaters, The EPA began a voluntary program in 2007 with the input of hydronic heater manufacturers and regulators. As of May 15, 2015, all residential hydronic heaters manufactured and sold must be EPA-certified and emit no more than 0.32 lbs per mmBTU. Based on the EPA central heater database, certified hydronic heaters range from 39% to 90% efficient. As of December 2017, the average certified outdoor wood boiler is 66% efficient and the average pellet boilers is 84%.

State Policies Addressing Use of Outdoor Wood Boilers:

While the federal government regulates emission limits for all states, each state or city or county can regulate property line set-backs, stack heights, etc. or choose to ban outdoor boilers altogether. The state of Wisconsin compiled a nine-page list of counties and towns that banned or restricted outdoor boilers. The EPA maintains a list on stove and boiler restrictions as well. Many states have passed rules that establish property line setbacks and minimum stack height requirements to ameliorate problems and prevent installation in densely inhabited areas. These states include Indiana, Maine, Maryland, Massachusetts, New Hampshire, New York, Oregon, Pennsylvania, Utah and Vermont. Washington State, Oregon and much of California have effectively banned use of outdoor wood boilers.

Stack of Logs

More background and resources on outdoor boilers

  1. AGH's blog of the legacy of outdoor wood boilers click here

  2. Resources, links and advice from the state of Minnesota

  3. News coverage and consumer input from Popular Mechanics

  4. Central Boiler falsely claims Outdoor Boilers are cleaner than wood stoves

bottom of page