If you'd rather burn the smoke from your stove than clean
it from your chimney, look into . . .
In the last issue of MOTHER, we reviewed the progress
that's being made toward developing clean-burning,
efficient wood stoves. The latest high-tech wood burners
use 30% less wood and emit up to 90% fewer pollutants than
did the best heaters built only five years ago. However, a
lot of us simply don't have roughly $1,000 to lay
out for the latest catalytic-converter-equipped wood
Luckily, there is a course of action available that's a
great deal more affordable than purchasing a complete new
wood stove and that still provides much of the
efficiency improvement and emissions reduction made
possible by these state-of-the-art combustors. There are,
you see, over a half-dozen catalytic retrofit devices on
the market today, and test results show that they offer
significant performance gains over a plain old airtight
heater. If you're in the market for such a device, here are
some of the things to look for.
Any retrofit catalyst is a compromise, because the stove
that it's installed in was not designed to insure an
adequate supply of oxygen and good mixing of the smoke and
oxygen at the combustor. Also, add-on catalysts are often
positioned farther from active flames than are designed-in
units, so the temperature of gases entering them is
generally lower. This means that the add-on (and
particularly the external) catalyst may be reluctant to
"light off" at the beginning of a burn or after
Catalyst retrofits that are positioned inside the firebox
offer some obvious advantages. (MOTHER presented plans for
a build-ityourself model on page 162 of issue 79; see page
128 for back issue ordering information.) Their close
proximity to the burn zone allows them to get into action
early and keep working until there's little left but coals.
Having the unit too close to the fire can, however, be a
liability. If adequate precautions aren't taken to prevent
flames from reaching the ceramic monolith, thermal shock
can quickly destroy the catalyst: There have been reports
of combustors that disintegrated after only a few months'
use in stoves designed without adequate flame impingement
protection. Internal combustors are probably best suited to
stoves that are used continuously at low to medium heat
Many designers, including Robert Vincelwho developed the
Riteway internal'and the Uni-Com external catalyst
retrofits-have concluded that the stress to the combustor
inside a stove isn't generally worth the gains provided by
that position. Vincel's Uni-Com uses elaborate mixing
geometry to insure good distribution of gases, and is
fitted with cast refractory to give the unit thermal mass.
The latter measure helps the combustor get through
transient cool conditions-such as occur during
reloading-without dropping below ignition
Tests have been done on three retrofit cat alysts by
Shelton Energy Research for the New York State Energy
Research and Development Authority. The evaluation was
limited to one stove design, and Jay Shelton suggests that
the numbers shown in the accompanying chart could have been
different if a variety of appliances had been used.
Specifically, some retrofits add secondary air to insure
good oxygenation. This could be an advantage on some
heaters and a disadvantage on others. Some combustors are
longer than others, and the extra length could improve
performance on larger stoves with high flue gas velocities.
Furthermore, a number of add-ons are also restrictive (that
is, they slow the exhaust gases and reduce the maximum burn
rate), which may provide better heat transfer in stoves
that are leaky. (Restrictions may also protect the
combustor by preventing high burn rates and attendant flame
But, whether you choose an internal or external catalyst
retrofit, there are operating techniques that can help you
get the most out of the device. Catalysts thrive on just
those conditions that tend to plug the chimneys of
conventional airtights with creosote. Once the catalyst has
gone into action, it will work best when the firebox is
loaded with fuel, the air controls are adjusted for a low
burn, and the fire is allowed to smolder. In fact, those of
us at MOTHER who use catalyst stoves have found that little
attention needs to be paid to the heater's operation. A
typical day consists of jamming the firebox full first
thing in the morning and again before going to bed. A
12-hour burn is within easy reach, and the heat output
remains quite stable over that period.
Unfortunately, there's only one way to be absolutely sure
that the catalyst is working. Despite all the
advertisements that show the combustor glowing, this
situation only occurs for, at most, a couple of hours
during the burn cycle; most of the time, the catalyst is
working just fine without emitting any visible radiation.
Only a dual-probe thermometer, with one sensor before the
combustor and one after, will show with assurance whether
gases are being burned in the catalyst. (Companies that
market such devices include Vermont Technology Group, Inc.,
Morrisville, VT 05661, and Lehman Engineering, P.O. Box
487, Mazomanie, WI 53560.) A surface thermometer will give
you a general idea of whether the combustor is generating
heat, but will give little clue to the combustor's overall
effectiveness. Of course, a reduction in the amount of
smoke coming from the chimney is a general indicator of
combustor light-off, and heavy build-up of black, shiny or
gooey creosote (rather than tan or brown soot) is a sure
sign that the catalyst hasn't been working for some time.
Don't assume, however, that a properly operating catalytic
converter will eliminate creosote. Some material
will still accumulate, and chimney maintenance should be a
regular part of your routine.
The list of manufacturers of retrofit catalytic converters
that accompanies this article includes most, if not all, of
the devices that are presently available for universal
application. Many stove manufacturers make kits designed
specifically for their products (Riteway is one company
that offers such a device), and you should check first with
the local dealer who handles your brand of heater. Then, if
that fails, consider a universal retrofit. You won't regret
Applied Ceramics Versagrid
P.O. Box 29664
Atlanta, GA 30359
4041448-6888 (to locate nearest dealer)
External catalytic dampers and cata lytic converter
retrofits that fit 6", 7", I and 8" flues. Top or rear
exhaust. Catalytic converter kit retails for `$139.95.
Five-year limited warranty.
Arden Industries Smoke Genie
P.O. Box 565
Spruce Pine, NC 28777
An internal catalytic retrofit that mounts in most stoves
without internal baffles. Catalytic converter encased in
ceramic housing. Sevenyear limited warranty. Retail price
Rt. 6, Box 131
Elizabethton, TN 37643
( to locate nearest dealer)
More than six different models for external and internal
retrofit to flue pipes, freestanding stoves with and
without internal baffles, top or rear exhaust, and
fireplace inserts. Retail from $94.95 to $119.95. Limited
warranty on catalyst.
Catalytic Damper Corporation Intensifire
P.O. Box 188
Flint Hill, VA 22627
8001643-5827 or 7031675-3011
T wo external retrofit models: Intensifire 2000 has large
combustor and fits 6", 7", and 8" flue pipes. Comes with
probe thermometer and fiveyear warranty for $199.95.
Intensifire 1000 fits 8" flue pipes (adapters available for
others) and has shorter catalyst. Two-year warranty.
Retails for $99.95. Adapters for rear exhaust available for
Metal-Fab Smoke Consumer
P.O. Box 1138
Wichita, KS 67201
( to locate nearest dealer)
Two external models (P9C and P10C) can be top or rear
mounted and fit 8" flues. Adapters allow use on 5", 6", or
7" flues also. Stainless steel wire mesh catalytic
converter. Limited one-year warranty.
Nu-Tec Incorporated .
P.O. Box 908
East Greenwich, RI 02818
Internal and external retrofits for freestanding stoves and
fireplace inserts. Limited five-year warranty. Top or rear
exhaust for 6", 7", or 8" flues. Retail prices from $129.95
Bridgewater, VA 22812
An external retrofit that fits 8" pipes but which can be
adapted to other sizes. For top or rear exhaust. Limited
oneyear warranty. Retail price $199.50.
Sotz Retrofit Catalysts
13628S Station Rd.
Columbia Station, OH 44028
80013219892 or 2161236-5021
External retrofits for 6" and 8" flues and for Sotz
two-drum stoves. Oneyear limited warranty. Retail (with
shipping) $110.97 to $116.97.