Fire up the old flame with a retrofitted combustor

By , Staff writer of The Christian Science Monitor

One recent winter morning I went outdoors to check out the chimney just 25 minutes after refiring the old black wood stove in the basement of our cottage here. Normally it would belch smoke for an hour or more under these circumstances, until all the wood had been converted to charcoal. Yet on this crisp morning not a trace of anything was visible coming from the chimney. Even heat waves seemed noticeably absent.

The stove, which is no longer being manufactured, is as basic as they come - barrel-shaped, with a small baffle just below the flue. On its own it could never be the largely pollution-free device it was proving itself to be that morning.

What made the difference? A retrofitted catalytic combustor, or smoke burner, placed right on top of the stove where the smoke exits into the flue.

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Retrofits are afterthoughts. They can never work as effectively as the combustor built into a stove that has been specially engineered for the purpose. But early signs are that this one is performing particularly well.

Under coming federal Environmental Protection Agency regulations, sales of new stoves that do not meet stringent clean-burning standards will be banned from the market beginning in 1988. It will still be perfectly legal to own non-conforming stoves, such as the one I now have, if they are installed prior to the end of this year.

So why did I bother to attach a catalytic burner to my old but perfectly legal stove? Simply because it pays for me to do so. Beyond cleaning up the air in my immediate environment, it will cut down on the amount of wood I burn each heating season and dramatically reduce the formation of creosote in my chimney. The latter is a safety as well as a convenience factor.

Peter Albertson of Nu-Tech Inc., makers of catalytic retrofits, states that, on average, retrofits should prove about two-thirds as effective as the built-in version which can boost combustion heating efficiency by as much as 50 percent. You can seldom get the perfect mix of air with the exiting gasses for optimum burning and heat retention in a retrofit, he says. On the other hand, the retrofit is almost as good at reducing creosote-forming gasses.

When my chimney was showing no visible emissions, the catalyst was burning at around 1,200 degrees F., which is perfectly acceptable but ``unnecessarily high'' in Mr. Albertson's view. When a light white plume is showing, he points out, most of that is condensing steam. No plume indicates that enough heat is exiting the chimney to disperse the water vapor before it can condense into visible steam. The idea, of course, is to keep as much heat as possible indoors. Albertson suggests that between 800 and 1,000 degrees F. is an efficient burning temperature.

If you attach a retrofit combustor to a stove, be prepared to work a little with it during the first few weeks. It's rather like getting behind the wheel of a new car: you know how to drive, but it behaves differently from the old one. No two stoves or two chimneys are quite the same, so the ideal air intake setting in one home won't necessarily work in another.

Fully engineered catalytic stoves have two, even three air intake settings. The retrofitted stove invariably has only one, so that even minor variations in the setting can result in major temperature variations. This was my experience at first, but after several firings it seemed that I could hit the right setting fairly soon.

Already my wife and I have noticed a significant drop in wood consumption for the same heat output, and we don't have to feed the stove as often. Presumably, the chimney isn't sooting up anywhere near as much either.

A related story on wood stoves ran on the Home & Family page on Tuesday, Jan. 20.

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