Reprinted from MOTHER EARTH NEWS NOs 67, 76, 90 and 97.
In five short years, 28 manufacturers have risen to the
challenge of woodstove pollution.
MOTHER EARTH NEWS takes pride in the fact that over five years ago
(in issue 67) we took a hard look at one of our
own favorite forms of alternative
energy — wood heat — and admitted that it
had some serious environmental pollution problems.
In the intervening years, we've shared
current research on woodstove pollution . . .
offered all the advice we could on ways to lessen
one's wood burning impact (including a
build-it yourself retrofit catalytic combuster, in
issue 76, page 162) . . . and highlighted the new
commercial offerings — from retrofit
catalysts (issue 90, page 102) to a new design
that burns so cleanly it could conceivably be used
without a chimney (issue 9, page 24)! The
following piece, condensed from five years of our
wood stove coverage and amended with the
latest news, offers vital information about the
wood burning pollution problem and what you
can do about it.
Woodstoves and Environmental Pollution Problems
If you've spent any time contemplating the curl of smoke
from a woodstove flue, you've probably wondered just what
was in that cloud . . . and whether it contained pollutants
that might someday be recognized as harmful. But if you'd
asked the experts before June of 1980, when the Monsanto
Corporation completed a study for the Environmental
Protection Agency (EPA), there really wouldn't have been
much they could tell you. Up to that time, there was
precious little solid technical information about the
specific kinds and quantities of emissions produced by
residential wood-fueled appliances and environmental pollution problems.
Since the alarming results of that study were published,
though, scientists have rushed to get a handle on the
problem. And study after study has confirmed that
woodstoves, particularly the airtight models that became
popular in the 1970s, do pose significant pollution
problems. In some locales, woodstove pollution is quite
serious, constituting the major source of particulate
emissions. And on a national basis, wood burning produces a
significant share of some very dangerous compounds.
According to Dr. Dennis Jaasma, a wood-combustion research
scientist at Virginia Polytechnic Institute and State
University, the most threatening pollutants are
particulates, vapor-phase hydrocarbons, and carbon
monoxide. All of these substances can be drawn deep into
the lungs through normal breathing and thus pose various
respiratory hazards to those exposed to them.
Scientists don't know for sure what the annual contribution
of wood burning may be to the emission of these three
groups of compounds, but estimates have been made that the
numbers are 0.7%, 2.5%, and 4% respectively. (By
comparison, diesel engines contribute about 1% of the
national particulate emissions and are regulated by the
Environmental Protection Agency.)
But it's actually a subcategory of the
particulates and vapor-phase hydrocarbons that may be of
the greatest concern. It seems that woodstoves are prolific
producers of compounds known as polycyclic organic matter (POM). Many POM are known to be
mutagenic or carcinogenic, and it has been estimated that
woodstoves emit about 40% of the total annual load of these
compounds in our atmosphere. The EPA further estimates that
woodstoves produce 90% of the POM emitted from all sources
other than transportation — making them a far greater
concern than fossil fuel-fired powerplants or industry.
The Pressure Is On
The insistence of regulators that woodstove pollution be
controlled has played no small role in the development of
new wood burning technologies, and the ball may only have
begun to roll. Today, Oregon has a regulation that,
effective July 1, 1986, prohibits the sale of stoves that
fail to meet its emission requirements. Colorado, too, has
passed a law that will begin to take effect in 1987.
But the biggest player on the horizon is the United States
Environmental Protection Agency. In an uncharacteristic
show of expeditiousness — brought on at least in part
by legal pressure concerning POM from New York State and
the Natural Resources Defense Council under the Clean Air
Act — the EPA now plans to propose a woodstove
emissions rule by January 1, 1987, that might take effect
by the first day of 1988. What this means is that in a very
big hurry (perhaps less than two years from now), the
conventional airtight woodstove could be on its way to
The List of 28 Clean Certified Woodstoves
Today, there are 28 woodstoves certified for sale in
Oregon. (Only 19 of those can stand up to Oregon's more
stringent 1988 requirement.) However, with EPA's regulation
little more than one development season away, you can
expect to see the number of clean burners increase rapidly.
As it's said, necessity is the mother of invention.
At present, performance figures from Oregon's Department of
Environmental Quality (DEQ) make up the largest body of
data about clean-burning stoves. Still, though numbers may
not lie, they can certainly be misrepresented.
Consequently, when you go shopping for a clean-burning
woodstove, we encourage you to study performance claims
carefully. Efficiency and emissions offer a good basis from
which to begin selecting a woodstove, but there's more
involved in picking the right heater. The heat output, for
example, should be in a range that's useful for your house.
And it may be important to you that the firebox hold enough
wood for an all night burn at the desired heat output.
One way that manufacturers have gotten non-catalytic stoves
through DEQ testing is to use small fireboxes and prevent
air inlets from being closed beyond a certain point. So,
not all of the stoves listed by DEQ can be adjusted to a
low enough burn to prevent overheating in small,
well-insulated houses . . . and some can't achieve a
great enough output for long enough to keep a
large, poorly insulated home up to temperature.
Beyond these practical concerns, several factors limit the
usefulness of the Oregon performance data to consumers.
According to Paul Tiegs, senior principal scientist of 72
Omni Environmental Service — the laboratory that did
most of the testing on the 28 stoves the listed efficiency
figures are accurate only to within plus or minus 5%. Thus
you shouldn't pick one stove over another strictly because
it can claim a few extra percentage points of efficiency.
Furthermore, the efficiency/emissions figures from Oregon
are adjusted to suit the climate and wood burning
conditions in that state. DEQ researchers studied the
habits of Oregon wood burners and determined that they fire
their heaters at medium-to-low rates (a heat output of
about 13,000 Btu/hour, or three pounds per hour in a
conventional heater) and in about six-hour cycles.
Consequently, the "weighted" average efficiency and
emission figures you might find in a manufacturer's
literature or in performance ratings on stove labels are
statistically biased toward 13,000 Btu/hour. If you operate
one of these stoves at more or less than that rate, the
absolute efficiency and emissions (as well as its
performance in relation to another heater) could be
Woodstove efficiency figures are inevitably likened to EPA
fuel mileage ratings for cars. The lessons are much the
same: Though these numbers are for comparison purposes
only — your actual efficiency and emissions "may
vary" — the performance of any of these stoves will be
significantly better than that of your present one. You'll
find that you're getting more heat from your wood
or — if you keep the stove turned down — that burn
time is dramatically extended.
If you're burning four cords of $100-per-cord wood each
year (and be realistic about what wood really costs),
stepping up from a 50% efficient black box to a 75%
high-tech stove will save you $130 in firewood alone in the
first year. Add to that the cost (or aggravation) of
chimney cleaning that you can save, and you've got a pretty
convincing economic argument for buying a new stove. The
health argument is even stronger: Using one of these stoves
can be a "Clean Air Act" of your own.