Testing Chemical Chimney Cleaning Products

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The purpose of chimney cleaning products is to prevent this: a roaring chimney fire.
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Six identical "airtight" steel stoves—equipped with DuraVent single-wall chimneys—were employed to perform the research on the four chimney cleaning products.
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Diagram shows the stovepipe setup used in the tests.
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Photo shows creosote accumulation in the untreated control pipe after the cleaning phase. Heat has caused the creosote to dry and swell. Some of the flakes have already fallen to the bottom of the pipes.
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Photo of stovepipe  A1 was taken in Series 3 before cleaning started, and is of an untreated (control) pipe.  
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Photo of stovepipe  A2 was taken in Series 3 before cleaning started, and is of a treated pipe.
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Photo shows creosote accumulation in a treated pipe after the cleaning phase. Heat has caused the creosote to dry and swell. Some of the flakes have already fallen to the bottom of the pipes.

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.

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 large-fuel-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. A deposit of this type 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.

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.

Overview of Tests Performed 

Series 1
  Wood type: Piñon*
  Phase I
   Description: Creosote accumulation phase with cool fires
   No. of Days: 3
  Phase II: Cleaning with regular doses of chemical cleaners
   No. of Days: 2
  Phase III: Cleaning with three times the regular dose
   No. of Days: 3
Series 2
  Wood type: Oak**
  Phase I: Creosote accumulation phase with cool fires, except for 10 minutes of hot fire during the last two days.
   No. of Days: 3
  Phase II: Cleaning with regular doses of cleaners
   No. of Days: 2
Series 3
  Wood type: Piñon
  Phase I: Creosote accumulation on top of previous accumulation, cool fires
   No. of Days: 3 1/3
  Phase II: Cleaning with regular doses
   No. of Days: 2
  Phase III: Cleaning with regular doses in an oxygen-rich environment
   No. of Days: 5 1/3
Series 4
  Wood type: Piñon
  Phase I: Prevention phase, using cool fires with regular doses of cleaners from the beginning
   No. of Days: 4
  Phase II: Prevention phase, cleaners at five times regular dose
   No. of Days: 5
  Phase III: Cleaning phase, hot fires and cleaners at five times regular dose
   No. of Days: 4
Series 5
  Wood type: Piñon
  Phase I: Cleaners at 5 times regular dose, one hot and two cool fires per day to approximately "typical" stove use
   No. of Days: 8 1/3
Series 6
  Wood type: Oak
  Phase I: Prevention phase, cool fires, cleaners at 5 times regular dose
   No. of Days: 6 1/3
  Phase II: Prevention phase, one medium fire and one cool fire per day, cleaners at 5 times regular dose
   No. of Days: 3 1/3 
  Phase III: One hot fire and one cool fire per day, cleaners at 5 times regular dose
   No. of Days: 3 1/3 

In this chart, one “day” equals three fuel loads, which was the average number of loads per day. Occasionally as many as six loads were burned in one day or as few as one, if the fires being burned were very hot or very cool, respectively. For example, in Series 6 there were actually 22 firing days and a total of 28 days of laboratory effort.

*Pinon, or Pinus edulis, is a moderately pitchy conifer.
**The type of oak used was Quercus turbinella.

Summary of Cleaner Performance, Overall Test Series

Chimney Sweep Soot Destroyer (Coughlin Products)
  Prevention phases: 26
  Cleaning phases:   31
  Average:           29
*Safe-T-Flue (Webster Industries)
  Prevention phases:  6
  Cleaning phases:   -4
  Average:            1
Red Devil Soot Remover (Meeco Manufacturing)
  Prevention phases:  7
  Cleaning phases:   20
  Average:           14
Cleans-Up (Charnas Industries)
  Prevention phases: 16
  Cleaning phases:   -2
  Average:            7
Control 1
  Prevention phases: -7
  Cleaning phases:   -5
  Average:           -6
Control 2
  Prevention phases:  7
  Cleaning phases:    5
  Average:            6 

These numbers represent the percentage difference between the particular system and the control systems. A positive number is not favorable: it indicates the chimney accumulated more creosote (or lost less) than the controls. For each phase of each series, we computed the percentage point difference between each test chimney and the average of the control chimneys. We then computed a weighted average of these numbers for each system with the weights for each test phase being proportional to the average amount of creosote accumulated (or lost) in all the chimneys for that test phase.

Creosote prevention phases started with clean chimneys or directly followed, without mechanical cleaning, a previous prevention phase. Chemical cleaners were used right from the start, with no separate creosote-accumulating, nonchemical burns beforehand. A variety of fire conditions–mostly hot–were used during the prevention phases.

Creosote cleaning phases started with dirty chimneys, and chemical cleaners were then applied. The fires were either hot or a mixture of hot and cool. 

*Safe-T-Flue reports it now has a different formulation on the market.

Red Devil Soot Remover, which was used in these tests, and Red Devil Creosote Destroyer are different products. Creosote Destroyer was not yet on the market when this research study began.

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).