First just what is Creosote?
Creosote is really a mixture of condensed gases left over from incomplete combustion of wood or coal. What most call creosote is actually often a mixture of tar, creosote and ash in reality. When looking at oil burning appliances most think of it simply as soot.
Realistically there are a few types of creosote possible to be found in a chimney. We will discuss in some detail three of them and touch on the other two at the end.
The first, often called Stage one or Level one can be fairly easily removed with the proper tools. This is what dried creosote is when there is a fairly good combustion taking place and the pipes and chimney warm up enough to dry the condensed gases. In this type of creosote the fire did cause deposits, typically at start-up, however there was adequate air for adequate and speedy drying of the deposits. This is something a home owner or DIY person can do a fairly good job of if they take the time and are patient in their removal process – although as they are only pushing and pulling up and down it may take then an hour or more to adequately clean the average chimney (those who think they are finished in one or two pushes up and down are often sadly mistaken).
The second which is called Stage or Level two is a bit more tricky to remove the hard and shiny flakes. This is not nearly as easy to brush away but is still not terribly difficult with power rotary professional level sweeping equipment. This is very difficult to impossible to remove with the manual push brushes.
The third one, often called Stage or Level three is the hardest of any to remove. It occurs when the flue temperatures remain low, with incomplete combustion and allow for a very slow drying of the creosote deposits. This is when the stove is turned way down and really never gets hot, when the chimneys are cold and uninsulated, when using wet/unseasoned wood or old punky wood, when the chimney/flue is oversized for the appliance (an 8 inch chimney or larger on a six inch stove as an example) or even when the house is so tight that the stove simply can not get adequate draw or draft – lacking combustion air supply. Third degree looks like a black shiny tar coating and will be hardened and shiny. It is an extremely concentrated source of fuel and will burn very hot if ignited. It can layer year after year and can become very thick – we did an outdoor furnace this week where it was an inch thick all around the chimney.
I did say there were actually five types and only mentioned three. The forth is actually the initial condensation of the creosote deposits before it drys and is actually a semi-liquid gummy material which can if thick enough actually run down the pipes. This will dry and become one of the three types mentioned earlier. The last one is more of a bubbly and expanded type which can occur after a chimney fire. This occurs during a chimney fire where the creosote is actually boiling and is not consumed before the fire goes out. This can actually cause further flue congestion and closure and is more like a light weight dried out sponge – often two inches or more thick on the walls of the chimney. It is fairly easily removed with a power rotary sweep. If you do not get regular annual cleanings however, and you get more Level three creosote filling this sponge material you can quickly and easily get 50 kg or more of creosote in your chimney. While the first fire may not have caused serious damage the second will be far more intense than was the first. The hard part here is that Stage or Level three creosote is very hard to remove.
Most sweeps use some sort of brushes to remove creosote and any Certified Sweep I know personally today will be using power rotary sweep equipment, simply because it does a better job – far better job in fact. These tools, like the manual brushes will quickly and easily plow through Stage one creosote. The power tools can also with a bit more work handle Stage two creosote build up – the manual brushes will struggle with these deposits but given enough time and persistence may get that as well – although there are flat metal brushes which although quite expensive do work fairly well. The very best by far however for Stage two creosote is a power steel rotary tool.
For Stage three the power rotary tools can also be quite effective – the manual tools are useless here. But even with power tools it can be a difficult job. This is where chemical removers come into play. Chemical removers however take time and do require a second trip by the Chimney Sweep. One of the most effective being CreAway, which can actually reverse many problems over time provided one changes their burning habits. By continuing to burn the same way as you did to develop the problem in the first place will not prevent further deposits and my application of CreAway is only a waste of money – well I can keep reapplying it but it is expensive to buy and apply. If the third degree is really bad there may actually be a case to remove the liner and reinstall!! But lets first look at the options – CreAway will work if there has been no chimney fire and the walls simply look like they have a tar coating on them. There is also a chain head for the power rotary sweep which can be rather effective on the hard to get Stage three creosote – contrary to what one would think, the chains will not break the chimney tiles. In all likelihood however in chimneys which have been abused to the point where Stage three creosote is present – the tiles are very likely already broken. Therefore it is very difficult to find a sweep who will use the rotary chains as ultimately they will be blamed for breaking the tiles. Regardless of this, it is an option and one of the most effective available. Keep in mind that without chemicals – even the specialized tools will only get the chimney and pipes clean to a point.
Now the bad news. There are times when the creosote is better not removed, even Stage three! These are masonry chimneys which have poor or no real joints between the tiles. And they are more common than one might think. I see them often with the chimney camera. Now with creosote buildup these gaps have become filled with potentially flammable materials and cleaning these chimneys does not in any way make them nearly as safe as you might hope.
With these chimneys one really needs to remove the old tiles completely and replacing with a new stainless steel liner. The reasons there are bad mortar joints or cracks in chimneys are numerous, but include masons who work too fast and don’t think it’s actually important to properly seal the joints, masons who use the improper mortar which dries too quickly and falls out, shifting or moving of the whole chimney over time (this can even cause cracking in times – as can heat and expansion/contraction – can happen to the best chimney work), a chimney fire has occurred – which will almost always cause tile cracking and mortar is demolished. Older stoves, dating back to the early 1980s and before had much lower burning efficiency abilities – they burned much more wood and did a much poorer job of it. This could send a lot more heat up the chimney – which could dry the creosote well. However, often times they were also pretty much shut down to a smoulder at which point they become creosote generators. Today the stoves are much more efficient – sending less heat up the chimneys and the homes tighter sealed – meaning the stove may lack combustion air. With modern stoves stainless steel insulated chimneys or stainless steel liners work far better as they heat quicker and more easily and are properly sized to the appliance. Bottom line is any wood stove can be safe if properly maintained – but lack of maintenance, annual cleaning by a professional and poor burning practices can lead to disaster.