Wood Burning Indoor Boilers

Indoor wood and pellet boilers are widespread in Europe and are steadily gaining in popularity in the US. Indoor wood boilers have been used in America for many decades, but they tend to be a more basic technology that is not very efficient or clean. Modern, automated pellet boilers (hot water) and furnaces (hot air) using bulk pellets offer homeowners virtually the same convenience as a fossil fuel furnace by feeding fuel automatically from a large storage area.  Both New Hampshire and Massachusetts offer generous rebates to install these systems.

indoor boilersModern indoor wood boilers can have oxygen sensors, microprocessors, and catalyst capabilities. This allows them to achieve very high efficiencies, in the mid 80s, HHV. They need to be loaded once or twice a day and hot water storage tanks ensure that they burn as cleanly and efficiently as possible. Hot water storage allows the full load of fuel to be completely burned, while extra heat is stored in the tank. This prevents the boiler from cycling on and off.

Modern pellet boilers and furnaces also have automated sensors to control combustion, along with automated fuel loading so that the operator may only need to clean out the ash tray once or twice a month. Pellet boilers and furnaces can be loaded daily with 40-pound bags of pellets, just like stoves. They may also have a bulk storage bin that holds several tons of pellets and is only refilled once or twice a winter.


For more info: http://www.woodheat.org/outdoor-boilers.html.


Wood Burning Outdoor Boilers

outdoor boilers

Outdoor wood boilers, also known as hydronic heaters, are a controversial technology that has spawned thousands of complaints and lawsuits across the country due to excessive smoke.  Recently, cleaner outdoor boilers have reached the market, but they can still be problematic in populated areas.

Outdoor wood boilers gained popularity in rural areas where fuel is abundant. They began as a very basic, unregulated technology that was advertised as being an affordable and efficient way to heat your home. 

The EPA began a voluntary program in 2007 instead of developing national regulations. Under the voluntary program, companies that meet certain emissions and efficiency standards for at least some of their units can advertise as “EPA Phase II Qualified.” Based on independent third party testing, these boilers are estimated to be 55 to 65% efficient, while the unqualified ones are 35 to 55% efficient. The list of hydronic heaters that qualify for the EPA's Outdoor Wood-Fired Hydronic Heater program is here. States that have passed regulations to allow only the cleaner, Phase II units to be installed are: Indiana, Maine, Maryland, Massachusetts, New Hampshire, New York, Oregon, Pennsylvania and Vermont. Washington State effectively bans outdoor wood boilers.

The EPA is now in the process of making mandatory regulations, which will likely take effect in 2014 thus requiring all states to only allow the installation of the cleaner, more efficient units.

According to the State of Washington Department of Ecology, "most OWBs employ very primitive combustion technology" and "are designed to burn wood at lower combustion temperatures and generally have shorter stacks, which emit smoke closer to homes and neighborhoods." Lower combustion temperatures result in less complete combustion, causing increased emissions of particulate matter. OWBs often run on idle periodically to avoid overheating the water, and produce large plumes of opaque smoke as they reheat after a cooling period.

For more information on AGH's comparisons of OWB regulations, click here.

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