Monday, May 18, 2020

Glaze Creosote Confession: The Potentially High Cost of Ignorance

This was my twenty-third winter season cooking on a woodburning cookstove, but I still have things to learn.  Truthfully, I'm kind of embarrassed to share the information in this post, but since the whole point of this blog is to help others enjoy cooking on woodburning cookstoves, I feel obligated.

First, some history:

The first wood cookstove that I used was the Qualified Range.  I bought it new in January of 1997 and had it installed in the little house with a pre-fabricated metal chimney.  I would say that the distance from the stove collar to the top of the chimney was probably less than twelve feet.  I never had any trouble with creosote accumulation in that setup.  However, I only used it from January of 1997 to May of 1998 because then I moved to the "big house."

When I moved into the "big house" on the farm, I had to wait a winter before I was able to get a new stainless steel liner put in the original brick chimney, but by the fall of 1999, I was again using the Qualified on a daily basis for cooking and heating.  The Qualified was in use in the "big house" from 1999-2011 when it was replaced by the Margin Gem.  During those twelve years, I had one chimney fire, but it started in the stovepipe of the stove and spread to the chimney.  It was easily extinguished by closing the drafts of the stove, and since it happened in the summer, it was not difficult to get on the roof and sweep the chimney clean again.  Had I been more diligent about keeping the stovepipe clean, the fire wouldn't have happened at all.

With the Qualified Range, there was never a lot of creosote in the chimney. I would sweep it in the fall of the year before daily firing of the stove began, and what creosote was present was always light, flaky, and easy to remove.  The creosote in the stovepipe was always the same, but would sometimes cling more stubbornly.

Now, the Qualified Range was not airtight.  It had the old style sliding drafts on the left side of the firebox, and though they were made well, there were some gaps that were inherent with that sort of stove construction.  Tiny gaps were also present in the top left corner of the firebox and where the outer front door latched to the cast iron of the firebox.  Further, the standard of fit and finish for the cast iron stovetop was lower than that of the Margin Gem.  If a bright fire was burning in the stove and all of the lights were put out at night, you could see tiny yellow flickers against the backsplash of the stove and on the kitchen ceiling.  Obviously, there were plenty of places where air could gain entrance to the stove even when it was shut down tightly.  Therefore, the Qualified could not hold a fire overnight or during the day when Nancy and I were gone to work and school.

The Margin Gem began its career in our kitchen in the spring of 2012 and has been in daily use from late September or early October until May ever since.  Shortly after it was installed, I noticed that the creosote in the chimney was different.  Some of the dry, flaky, familiar stuff was present, but there was a coating of black, tarry stuff that was very smooth.  This, however, appeared to only be in the top three or four feet of the chimney, which is the part that sticks out above the roof line.  It was a thin layer, as I said, and I didn't think a whole lot about it.  I attributed it to the fact that the stove is airtight and also to the fact that because the Margin Gem has both a hyper-heat water reservoir and a waterfront for the range boiler, a lot of the heat from the fire was being absorbed before it had a chance to travel up the chimney.

I didn't think a whole lot about this new creosote.  Usually, after a summer of only intermittent firing--usually using small sticks that burn hot and quick--the hard, shiny stuff would sweep out of the chimney with the fall sweeping that began the continual firing season.

Fast forward to this last winter.  During the months when the Margin Gem is being fired daily, I sweep the chimney once per month as long as the roof is free of snow.  During December and early January, we were burning some mulberry wood which had been dead for at least six years, but was more wet than I would have liked.  When I went to sweep the chimney in early January, my chimney sweeping brush got stuck in the chimney.  The shiny, hard creosote had become quite thick on the inside of the chimney, and it was no longer just in the top three or four feet of the flue.  I had a really tough time getting my brush back out of the chimney, and I knew we had to do something.

My first thought was that we needed to have a professional chimney sweep come and clean the chimney.  I did some phone calling and discovered that where we live, professional chimney sweeps are few and far between, and they are really busy.  We would have had to wait a very long time before a professional chimney sweep would have been able to come to our house--in fact, I was basically told that we wouldn't be able to see a chimney sweep until after the heating season was over.

We couldn't wait that long.  During the winter months, the Margin Gem heats our home and our hot water, and it cooks nearly all of our food.  I was worried about the creosote situation and began doing some research. I learned that professional chimney sweeps use mechanized equipment to clean chimneys rather than just a steel brush on rods like I have.  I discovered that our nearest Menards carries such equipment and promptly plopped down around $150.00 for a set of chimney cleaning equipment that attaches to a drill.  (I didn't know that this kind of chimney cleaning equipment even existed, and I'll write a post about it sometime because it is worthy of a lengthy discussion by itself.)

I got my new purchase home and opened the package.  Having never known anything about this sort of chimney cleaning device before, the first thing I did was open the instruction booklet.  Among other disappointing information there (which I will discuss in a later post), the instruction booklet said that the chimney sweeping equipment was not for use on "GLAZE CREOSOTE."  There it was: a name for the stuff I had seen lining the chimney!

After more research, I knew how dangerous glaze creosote in a chimney can be (if ignited, it burns at a higher temperature than light, flaky creosote does).  That same research taught me that there is no mechanical way to remove it, so sweeping wasn't going to make any difference.  Glaze creosote must be removed chemically.  Even professional chimney sweeps must treat glaze creosote with a chemical first and then come back to sweep it later, and the powders and chimney sweeping logs commonly advertised and sold locally have no effect on this type of creosote.  Internet reviews told me that two different products were highly recommended for use in glaze creosote removal: Cre-Away and Anti-Creo-Soot.  These are environmentally safe products that convert the glaze creosote from a hard substance to flaky creosote which is easy to remove.  Unfortunately, neither of these compounds are sold locally, so we had to order online and wait for delivery.  For a few days, we limped along with a stove that was operational but obviously not breathing as well as she should.  Then we began the glaze creosote mitigation process.

The two chemicals we used to remove our glaze creosote.  (Because I know
someone will ask, the cookstove on the left is the ceramic base to a lamp that
sits on the corner of our kitchen table.)

The Process of Glaze Creosote Removal:

The sites I read told me that I should start by using the Cre-Away.  Cre-Away is a fine white powder which comes in a plastic bottle with a hinged nozzle on the top.  You apply the Cre-Away to the chimney by squeezing puffs of it up into the stovepipe and the bottom of the chimney.  Because our chimney is so tall, the directions on the bottle also recommended sprinkling it down from the top of the chimney.  As we had very little snow this winter, this was not a difficult process.

Once Cre-Away has been placed in the chimney, the next step is to build a hot fire in the stove to activate the chemical reaction.  The flue temperature has to reach a minimum of 300ºF in order for each of the products to work, so I moved the flue thermometer that we have on our Jotul heating stove to the stovepipe of the Margin Gem.

Cre-Away was amazing!  It wasn't long before I could hear chunks of creosote falling down the chimney.  For three days in January, as soon as I got home from school, I would take the stovepipe down, remove the pile of creosote that had fallen down the chimney in the last 24 hours, and re-apply the Cre-Away.

The next step was to use the Anti-Creo-Soot.  This is a liquid, and to apply it you spray it into a good hot fire.  You can see in the picture above that the Anti-Creo-Soot which I purchased was in a gallon jug.  You can purchase smaller spray bottles of this compound, but they are more expensive, so it was cheaper for me to buy the gallon jug and pour some into our own spray bottle.  For the first application of Anti-Creo-Soot, the directions say to apply 60 (that's right, sixty!) squirts to the inside of the firebox or directly onto the fuel.  In severe cases of glaze creosote, the directions recommend sixty squirts each day for seven days.  Twelve squirts per day after that is what they advise for keeping your chimney clean thereafter.  Again, flue temperatures must reach 300ºF, in order for this compound to be activated.

Anti-Creo-Soot was excellent too.  It was very easy to apply, and chunks of creosote continually rattled down the chimney, especially when the fire was first stirred up in the morning or upon my return from school in the evening. I continued to regularly take the stovepipe down and clear away the piles of creosote left in the elbow at the bottom of the chimney.

Finally, a thorough sweeping is in order.  I am happy to report that this sweeping was easy, and I've never seen so much creosote come out of the chimney at once.  The Margin Gem was breathing freely again, and I could breath a sigh of relief!

I continue to squirt Anti-Creo-Soot into the firebox occasionally--especially when I know I'll be sweeping the chimney soon--and the effect that it has had is remarkable.  I cannot say enough good things about both of these products!


Here is an abbreviated list of the new things I know after having dealt with this situation:

1. Only burn dry fuel!  I knew this but admit to not prioritizing our fuel supply as well as I should have.  Also, I was under the impression that creosote only formed from wood that was wet because it hadn't been dead long enough.  Not so!  Wood that has been "seasoned" for adequate time but has been allowed to become wet again is just as susceptible to depositing creosote in a chimney.

2. There are different types of creosote, so you must pay attention to what is present in your chimney.

3. Glaze creosote can be removed by a do-it-yourselfer; you don't have to hire a chimney sweep if you are able to access your chimney yourself.

4. Glaze creosote can only be removed by using chemical compounds to loosen it before it can be swept away.

5. Cre-Away and Anti-Creo-Soot are awesome!  They are very effective in glaze creosote removal and are easy to use.

I hope that embarrassing myself and letting you all in on my former ignorance proves helpful to someone and that I can save someone else the danger of a chimney fire or the expense of hiring out work that one can do oneself.  Be safe!


  1. Jim,

    Great information! Thank you.

    Please don't be embarrassed about this topic. We've been heating with wood for 30 years and have never experienced glaze creosote in the flue. So I wouldn't have known what to do about it if I found it -- until now.

    I have always thought highly of mulberry for firewood. I don't get much, any more, but when we lived in Iowa, it was a common fuel for us. I confess, I too have burned wood that was wetter than it should have been -- though, as you wrote, properly cured, otherwise. So far, it has only been annoying. But you've given me something to watch for.

    Harvesting firewood is at the top of the list, right now, though rainy weather has been a hindrance. So far, I have hauled in mostly elm and ash (both green and white). I have cut a little black cherry and more sassafras than I care for (which isn't much).

    I wish you a great summer!

    1. Thanks for the support, Brett! We woodturners have to stick together.

      We're still firing the Margin Gem every day, but I have a good jump on next season's firewood. So far a lot of black locust. I don't like the smell of the smoke, but it burns good, long, and hot. We have a lot of mulberry in our future too. My brother came with his hay grapple on the tractor and pulled some bulldozer piles apart for me to work on cutting up. Been dead for a good long time, and now if I can get it under dry cover, it will be good burning this coming winter.

  2. Thank you for sharing about your experience. We don't have a wood burning stove anymore, but maybe we will again in the future. You can't beat that heat for warmth.