TESTING CHEMICAL CHIMNEY CLEANERS

Issue # 71 - September/October 1981

If you've been looking for a way to tame the buildup of creosote in your woodburner's chimney, you can check one possibility off your list.  

Jay W. Shelton
and Cathleen Barczys

For the last century, chemical "chimney cleaners", "soot removers", and various other stovepipe "deposit modifiers" have been available to consumers searching for an alternative to the frequent chimney inspections and the sweepings that most coal— and woodburning appliances call for. Such chemical cleaners are usually dry mixtures of various compounds and/or elements, but at least one product is liquid (an aqueous solution). Whatever form they take, the compounds are put on (or sprayed into) the fire, and their manufacturers claim that the mixtures can help keep a chimney clear of creosote, while also serving to minimize the buildup of deposits inside a stove's combustion chamber and on its heat transfer surfaces. Formulations are also available for oil burning appliances, and large quantities of them are used today in some industrial furnaces and boilers.

There has, in recent years, been a good bit of debate about just how effective the chemical chimney cleaners are in reducing creosote buildup in residential flues, but there's been little scientific evidence on which to base a decision. (To the best of our knowledge, the only previous study was conducted by the U.S. Bureau of Mines in 1929—30, and that piece of research investigated the effects of such products only on coal soot ...but not on wood-generated creosote.) Therefore, in an effort to determine the effectiveness of chemical chimney cleaners, we tested four representative name—brand products, simultaneously, in six identical "airtight" (steel) stoves. (One woodburner was used with each cleaner, and two served as untreated controls.) Creosote accumulation was measured by carefully weighing each flue before and after every test.

The chemical chimney cleaners we tested were selected (from a large group of products) on the basis of two qualifications. First, we wished to examine products that had strong national recognition and wide availability ...to make the results useful to as many consumers as possible. And second, we wanted to test compounds with widely varying compositions ... in order to analyze the effects of the several different chemical formulas employed by the various manufacturers. Consequently, some products that do have wide national recognition and availability weren't included because they were similar in composition to other cleaners that we did test.

A typical test series began with the cleaning and weighing of each and every test section of the chimneys. Then, after the stovepipe had been reassembled, the stoves were loaded and lighted. A normal evaluation run consisted of firing for 8 to 12 hours per day, five days a week, with an average of three loads of wood being burned daily. The power output, wood type and moisture content, cleaner dosage, and length of test series were varied over a full seven months of testing.

Stack temperatures were continuously monitored, to insure that the stoves were all running alike, and to identify any chimney fires that occurred (since the ignition of deposits would have altered the creosote in the chimney and affected the weights that were being checked).

CONCLUSIONS

The particular brands of chemical chimney cleaners that we chose didn't show any substantial effectiveness in our tests. We burned both oak and pine (using seasoned and green wood separately) in both cool and hot fires, and tried using normal and larger-than-normal applications of each product. We looked for signs of any prevention of creosote buildup or of its disappearance once formed ... for evidence of its failing in flakes down the chimneys ... and for changes in either the creosote's brushability or its flammability. Although we did see some such transformations take place, they were just as evident in the untreated systems as they were in the treated ones. Thus we don't attribute any of the positive effects to the chemicals themselves, but rather think that factors such as temperature, which were common to all the systems, played the major role in changing the nature of, or reducing, creosote.

In fact, in our tests, temperature was clearly a more important contributor to the reduction of creosote accumulation than was the use of any one of the chemical chimney cleaners. In general, relatively small, hot fires tend to be cleaner-burning (producing less smoke) than do largefuel load, smoldering fires ... thereby substantially lessening the rate of creosote buildup in the first place. And, once a tar glaze has formed in the chimney, a hot fire tends to transform it into a dry, flaky deposit ...which is light in weight, may fall off the chimney walls of its own accord, and (even if it does not drop) is much easier to brush away than the original gooey creosote. (See the accompanying photographic representation of such changes in creosote form.)

High temperatures, however, are not a cure—all for creosote problems, since an unusually hot fire will be the type most likely to ignite creosote and produce a chimney blaze. Lighting a small, intense fire once a day can be an effective way to reduce creosote formation, but doing so could also prove to be a dangerous practice unless one inspects the flue often enough to insure that no substantial (1/4" or more in thickness) deposit has formed.

In short, then, none of our test chimneys was rendered completely clean by either the chemical additives or by heat. A considerable amount of creosote always remained in the pipe until it was removed by brushing. It's entirely possible that, in spite of our negative findings, some chemical chimney cleaners do work in some cases. Although we believe that our selection of products and our testing conditions were representative, it was—of course—impossible for us to test all the available cleaners in all types of chimneys with all kinds of creosote.

However, even if some chemical chimney cleaners do sometimes work, it's evident that they don't always work ...both laboratory records and real-world experience prove the point. Therefore, it can be quite dangerous for anyone who uses a flue treatment compound to assume that it's working. Such complacency may well result !n less frequent inspection and/or cleaning ...which could result in a chimney fire. Frequent checking for creosote deposits and sweeping when necessary are still essential chores for anyone who heats with wood!

AUTHORS' NOTE: This research project was largely sponsored by Shelton Energy Research. We gratefully acknowledge partial support from Metalbestos Systems, and contributions of equipment from DuraVent Corporation and Oliver MacLeod, Ltd. (the manufacturer of ProJet chimney).

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