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Outdoor Wood Burning Gasification Boilers/Furnaces
When you burn wood under "open" conditions (which includes most wood stoves), it
burns at about 1200 degrees. This is hot enough to burn only the volatile oils and
some of the gases in the wood, but not the wood itself - which is why relatively large
amounts of unburned wood is deposited as ash or escapes up the chimney as smoke. .
The gasification process burns wood under such conditions that it cooks out the
carbon monoxide, hydrogen, and other trace gases. This occurs in the primary
combustion chamber very similar to a wood stove, except the oxygen is limited so it
produces carbon monoxide instead of carbon dioxide.
From there, the wood gas travels through a ceramic nozzle to a secondary combustion
chamber. At some point in, or just after the nozzle, more air is injected which
combusts the wood gas at about 2000 degrees and burns any remaining ash/smoke
particles suspended in the stream of gas and smoke.
The super heated flue gas then travels through a heat exchanger in the furnace
transferring the heat to water used to heat the house.
burns at about 1200 degrees. This is hot enough to burn only the volatile oils and
some of the gases in the wood, but not the wood itself - which is why relatively large
amounts of unburned wood is deposited as ash or escapes up the chimney as smoke. .
The gasification process burns wood under such conditions that it cooks out the
carbon monoxide, hydrogen, and other trace gases. This occurs in the primary
combustion chamber very similar to a wood stove, except the oxygen is limited so it
produces carbon monoxide instead of carbon dioxide.
From there, the wood gas travels through a ceramic nozzle to a secondary combustion
chamber. At some point in, or just after the nozzle, more air is injected which
combusts the wood gas at about 2000 degrees and burns any remaining ash/smoke
particles suspended in the stream of gas and smoke.
The super heated flue gas then travels through a heat exchanger in the furnace
transferring the heat to water used to heat the house.
Outdoor wood burning gasification boilers/furnaces are now being offered in response
to the backlash against traditional, smoky, outdoor furnaces. The gasification process
practically eliminates smoke and reduces emissions to comply with current EPA
standards.
Traditional outdoor wood furnaces average 1.8 lbs of particulate emissions (smoke)
per MMBtu (one million BTU of heat input). The current standard set by the EPA is 0.60
lbs/MMBtu.
Outdoor furnaces sold in Maine after April 1, 2008 must comply with Phase I of Maine's
rule (0.60 lbs/MMBtu) and furnaces sold after April 1, 2010 must comply with Phase II.
Phase II has an emissions limit of 0.32 lbs/MMBtu.
The new, EPA compliant gasification boilers can be distinguished from traditional
outdoor furnaces by the "EPA Orange Tag Approved" label. However, not all "EPA
Orange Tag Approved" outdoor furnaces meet the stricter standards imposed by
individual states.
to the backlash against traditional, smoky, outdoor furnaces. The gasification process
practically eliminates smoke and reduces emissions to comply with current EPA
standards.
Traditional outdoor wood furnaces average 1.8 lbs of particulate emissions (smoke)
per MMBtu (one million BTU of heat input). The current standard set by the EPA is 0.60
lbs/MMBtu.
Outdoor furnaces sold in Maine after April 1, 2008 must comply with Phase I of Maine's
rule (0.60 lbs/MMBtu) and furnaces sold after April 1, 2010 must comply with Phase II.
Phase II has an emissions limit of 0.32 lbs/MMBtu.
The new, EPA compliant gasification boilers can be distinguished from traditional
outdoor furnaces by the "EPA Orange Tag Approved" label. However, not all "EPA
Orange Tag Approved" outdoor furnaces meet the stricter standards imposed by
individual states.
By the way, the outdoor wood furnace has been
officially renamed "Hydronic Wood Furnace" by the
American Society for Testing and Materials to more
accurately describe what has also been known as a
"wood boiler."
The term "boiler" suggests these devices operate
under pressure and produce steam for heating, when
in fact, most outdoor wood boilers operate under
zero pressure and produce no steam, only hot water.
That being said, the terms "furnace" and "boiler" are
still used interchangeably on various manufacturers'
websites. Back to gasification; here's how it works:
officially renamed "Hydronic Wood Furnace" by the
American Society for Testing and Materials to more
accurately describe what has also been known as a
"wood boiler."
The term "boiler" suggests these devices operate
under pressure and produce steam for heating, when
in fact, most outdoor wood boilers operate under
zero pressure and produce no steam, only hot water.
That being said, the terms "furnace" and "boiler" are
still used interchangeably on various manufacturers'
websites. Back to gasification; here's how it works:
| Central Boiler E-2300 Classic Wood Gasification Boiler |
With an efficiency rating of 85%, wood gasification is about 30% more fuel efficient
than the typical wood burning stove or furnace. To put it another way, you need 30%
less wood to produce the same amount of heat.
Some manufacturers of outdoor wood burning gasification boilers also offer indoor
models. These are basically the same as the outdoor model minus the shed. Prices
range from $7,000 - $10,000, which compares favorably with traditional outdoor wood
burning boilers.
Here's a link to the current list of EPA Orange Tag Approved outdoor wood burning
gasification boilers.
than the typical wood burning stove or furnace. To put it another way, you need 30%
less wood to produce the same amount of heat.
Some manufacturers of outdoor wood burning gasification boilers also offer indoor
models. These are basically the same as the outdoor model minus the shed. Prices
range from $7,000 - $10,000, which compares favorably with traditional outdoor wood
burning boilers.
Here's a link to the current list of EPA Orange Tag Approved outdoor wood burning
gasification boilers.
Ash and some small chunks of wood from the primary burn chamber get
blown through the nozzle into the secondary chamber. This type of furnace
does not need an ash box.
blown through the nozzle into the secondary chamber. This type of furnace
does not need an ash box.