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Outdoor Wood-Fired Boilers
Outdoor Wood-Fired Boilers
Outdoor wood-fired hydronic heaters, also called outdoor
wood-fired boilers, are not allowed in the state of Washington
at this time. This site is designed to help you get the facts before
purchasing a wood-fired boiler. If you have any questions about
outdoor wood-fired boilers, please contact us.
With rising energy costs, more Washington residents are using
wood as a source of heat and hot water. But not all wood heat is
the same. EPA tests and certifies indoor wood stoves for
emissions, but does not test or certify outdoor wood-fired
boilers. Because outdoor wood-fired boilers are used year-round,
they burn much more wood than wood stoves do. They can emit
nearly twice as much smoke per hour as an EPA-certified wood
stove. The air pollutants in this smoke are bad for your health
and that of your family and neighbors. They also harm the
environment.
What are outdoor wood-fired boilers?
Outdoor wood-fired boilers are wood-fired water heaters that are located outdoors or are separated from the space being heated.
The fires in the large fire boxes heat water that is circulated into the home through underground pipes. The energy may be used to
heat houses, shops, domestic hot water, greenhouses, swimming pools and spas.
Indoor wood-fired boilers are subject to the same regulations as outdoor wood-fired boilers.
Are any outdoor wood-fired boilers legal in Washington?
Not at this time. However, Ecology is willing to consider allowing outdoor wood-fired boilers to be sold in Washington
if the manufacturers can show they meet Washington's standards. To show an outdoor wood-fired boiler meets Washington's
standards, a manufacturer must:
- have the device tested using a test method that Ecology
considers adequate and acceptable; and
- submit test results to Ecology showing the device emits no more than 4.5 grams of fine particles per hour.
To date, no manufacturers have shown they meet these requirements.
Ecology also wants to be sure that stack height and setbacks are sufficient to protect the health of people in the neighborhood.
EPA has a voluntary program for manufacturers of outdoor wood-fired boilers. Boilers that are accepted into this program meet stricter guidelines and pollute less than older models.
However, test results for this program have been achieved using a hardwood (oak) test fuel, which may under-report the amount of smoke emitted. Manufacturers need to provide test results
using Douglas fir, which is the standard test fuel used for wood stoves and other wood burning devices.
Get more information about EPA's voluntary program.
What causes outdoor wood-fired boilers to smoke?
Manufacturers continue to work on improving the efficiency of outdoor wood-fired boilers.
Early models use very primitive combustion technology that cuts the air supply to the firebox
when a set temperature is reached. This causes large amounts of smoke. Most of the smoke emitted
is fine condensed organic material that does not burn under cool, low-oxygen conditions. Burning
wood that is too wet can also cause poor combustion and heavy smoke. (State law says wood to be
burned must have less than 20 percent moisture content.)
How can smoke from burning natural wood be harmful?
Wood smoke from wood stoves and wood-fired boilers is harmful because it contains very fine particles.
These particles are so small they can be carried deep into the lungs where they cause significant health
problems such as asthma, lung diseases, heart diseases and death. These particles can also increase the
risks of certain types of cancer. Breathing smoke is especially harmful for children, the elderly, and
people with heart and lung problems. It is estimated that fine particle air pollution costs citizens of
Washington hundreds of millions of dollars each year in health care costs and lost productivity due to illness.
If I want to burn wood, what should I do?
- Buy a wood burning device that is certified by EPA, and that is as clean and efficient as possible.
- Consider your neighbors. Burning wood in dense residential
neighborhoods may never be a good idea, but it is especially bad during temperature “inversions,” when the air is still and cold.
- Have an energy expert inspect your home. You may find that more
insulation or other energy saving improvements may be a better
investment than an expensive wood heating device.
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