Wood savings: burn the smoke, too

If ever a man believes in getting the most out of his wood stove every time he stokes up, it is Robert V. Van Dewoestine of Corning, N.Y. He burns the wood and -- get this -- the smoke as well.

In his opinion, wood smoke is a secondary fuel, a complicated mixture of unburned gases, including hydrogen and methane -- so why waste it up the chimney.

As a result, Dr. Van Dewoestine gets a warmer home from every firing; his wood pile lasts somewhat longer; his chimney stays a whole lot cleaner; and he feels good about not adding to the pollution load in the atmosphere.

What makes all this possible is a catalytic combuster, an offshoot of the technology that brought the catalytic converter and cleaner exhaust gases to the automobile.

When costly heating bills arrived on everybody's doorstep a few years back, Dr. Van Dewoestine, with several acres of woodlot for a backyard, turned to the obvious to lower home energy costs. But all the literature pointed to some inherent problems in wood burning, notably the creosote buildup in chimneys.

So Dr. Van Dewoestine, along with some of his colleagues at Corning Glass Works, set out to see if this was a problem that could be licked. Now they feel they have gone a long way to doing just that.

With some catalytic-converter experience behing them (Corning was involved in ceramic substrate development for the automotive catalytic converter), the scientists began working on a similar device that would clean up wood smoke. The idea was to burn the smoke so completely that almost nothing was left but carbon dioxide and a little water vapor when it exited up the chimney. That sort of perfection hasn't been reached, but nonetheless the scientists have gone a long way toward reaching the goal.

This is how the honeycombed combuster works:

Just before leaving the stove, the smoke passes through the combuster, which, in turn, lowers the temperature at which the smoke gases burn. Normally, the gases ignite at around 1,100 degrees F., but the catalytic enables them to burn at a moderate 450 degrees, the temperature at which many gases enter the flue.

As the smoke starts to burn, the combuster heats up. This markedly increases its efficiency, so that within a few minutes any remotely combustible gas within the smoke is totally consumed, adding additional heat to the house as well as reducing cleaning to a once-a-year chore.

Another major plus: creosote-producing softwoods can be burned in a combuster- equipped stove.

The value of the combuster is seen in the fact that some 40 percent of the heat in wood is contained in volatile materials that are driven off as gas. Well-designed wood stoves with a secondary air intake can get some of these gases to burn before they escape from the fire. Even so, tests show that between 20 and 30 percent better wood efficiency is derived from the combuster. Even at the lower end of the range this means that where you used to burn five cords of wood a year, now you will burn four.

On the other hand, you might find yourself burning two cords for every three you used to burn.

Why the wide range of fuel efficiency? Dr. Van Dewoestine explains it this way: "If you burn your wood with a wide-open damper to encourage a hot fire, more of the gases will be burned before the smoke goes up the flue. In that event the combuster will improve efficiency by about 20 percent. But if you go in for controlled burning with a partly closed flue and a long-lasting fire, many more gases will escape unburned in a conventional stove. Under these conditions the combuster improves fuel efficiency as much as one-third.

Having field-tested the combuster over two years at, among other places, Dr. Van Dewoestine's home, Corning offered its development to stove manufacturing companies with this proviso: Only stoves with a bypass system that enabled it to work even if the combuster got clogged for any reason would be allowed to include the combuster.

While better fuel efficiency is most likely to spark public acceptance of the combuster, lowering polution from the home wood-burning stove is likely to be the long-term promoter of this device.

Continued expansion of the use of wood stoves -- considered by the EPA to contribute more to pollution than domestic coal-burning stoves on average, according to a Monsanto Research study commission by the EPA -- could impose restrictions on wood burning.

Commenting on this problem in its Nov. 13 issue, Britain's New Scientist says: "In some New Hampshire valleys, especially prone to haze, atmospheric particulate matter from wood burning has reached concentrations high enough to place a restriction on industrial expansion." Put another way, a device to clean wood smoke may one day be mandated for all new stoves.

Meanwhile, several stove companies have shown interest in the combuster. Among the first to produce stoves equipped with the combuster is Franklin Industries, Inc., of Warwick, R. I. (The no-charge phone number: [800] 556-7382 .)

Two models, with heating capacities of 10,000 cubic feet, retail for $950 and show that the combusters will last at least two years without any loss of efficiency. Dr. Van Dewoestine says they could be effective for many more years.

"We don't know because we've only been testing for two years," he adds.

Should the idea catch on in a big way, then combuster prices will come down markedly because of the economies of large-scale manufacture.

As yet, the combuster is not available as a retrofit for existing stoves, but such a system is in the development stage