Testing Chemical Chimney Cleaning Products

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

| September/October 1981

071 chimney cleaning products - chimney fire

The purpose of chimney cleaning products is to prevent this: a roaring chimney fire.


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 wood burning appliances call for. Such chemical chimney cleaning products 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. That piece of research investigated the effects of such products only on coal soot, not on wood-generated creosote.) Therefore, in an effort to determine the effectiveness of chemical chimney cleaners, we tested four representative name-brands, simultaneously, in six identical "airtight" (steel) wood 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 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).

Testing 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.

9/15/2014 5:19:31 PM

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5/18/2014 5:06:00 PM

Mix: 5lbs Copper sulfate + 1lb Trisodium phosphate powder detergent. Every 10 or so fires, place two heaping Tablespoons of this mix in an envelope and toss it atop a hot fire. When it comes time to sweep, instead of black peanut brittle like creosote, you'll find a crumbly dusty like accumulation that quite easily brushes away. This has proven true for several years, heating my home with hardwood, cast iron woodstove, in an insulated stainless steel flue. Prior to using this DIY mix, the top of my chimney was 'enameled' with black shiny creosote which was a real pain to remove.

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