Tar (or Creosote) can build up in your chimney or flue liner for several reasons and is a major cause of chimney and house fires. Firstly, it is important to know what it is. Tar is the residue left behind due to incomplete combustion of the gases and impurities which are released when you burn your fuel in your solid fuel appliance, whether you have a stove or an open fire. This can happen for a number of reasons which we will examine below.

Burning Wet Logs or Treated Wood

This (to me) seems to be the most common reason for tar build up for people with Wood Burning or Multi-Fuel Stoves. To preserve the life of your stove and chimney liner it is essential to burn quality wood. This means using only well seasoned or kiln dried logs and resisting the temptation to burn wood treated with paint or preservatives. The best way to ensure you are using dry wood is to get yourself a Moisture Meter. These are available almost everywhere and are quite inexpensive, although as with most things in life it is advisable to obtain the best quality you can afford. This meter has (usually) two prongs which you insert into your log and this will give you a digital read out of the woods moisture content. The figure you should be looking for is a reading of less than 20% (although 15% is considered optimal by most Chimney Sweeps). If you have access to kiln dried wood then this usually reads much lower than this so kiln dried is the safest way to go if you don`t have the means to season or store large quantities of logs.

Slumbering Your Stove/Fire or Burning at Too Low a Temperature

Your stove will have one or more air/ventilation controls fitted to it. This usually takes the form of a slide or a handle that you use to control how much air gets to your fuel to assist in the combustion process. When your stove or appliance is fitted it is vital to learn how to use these controls to get the most efficient burn possible. Your installer will supply you with instructions from the stove manufacturer but he should also verbally explain these controls to you in real time in order for you to fully understand how your stove functions.

If you close down the supply of air too much (it is amazing how many people do this habitually) then the fuel does not get enough air to burn off all the impurities/pollutants. This in turn means the gases are not hot enough to ensure the smoke emitted exits the chimney cleanly and in turn forms a build up of tar in your chimney/liner which is extremely combustable and can lead to house fires. This deposit can also lead to a complete blockage in the flue so no gases can escape at all. Gases such as Carbon Monoxide (CO) can leak back into your house and this is a potential danger to life. This is why it is also vital to have a correctly fitted CO detector in the same room as your stove.

It is worth knowing that the Government plans to bring in new controls in 2022 to control the type and quality of fuels that people are burning and to ensure that all appliances meet DEFRA requirements in order to reduce air pollution and to cut the number of chimney/house fires. It is important to note that they are NOT going to ban wood burning stoves as certain misleading articles in the press have claimed!

The Type or Location of your Chimney or Flue (inefficiency)

If you are burning the correct type of fuel at the optimal temperature (you can ensure this by using a stove pipe thermometer) and you still have a problem with the build up of tar then it is important to look at the efficiency of the flue/chimney and how the waste gases of combustion are kept hot enough to ensure they exit cleanly and efficiently.

Firstly, it may be that your chimney is not high enough and efficiency can be affected by surrounding structures such as other buildings or trees. Climatic conditions can cause down drafts that can affect how you chimney performs. Prevailing winds can also have an effect. Another issue can be that the chimney/flue is not insulated enough to ensure its efficiency. It could be that it is situated on an external wall or gable end and could require extra insulation to maintain efficiency. Much of these problems can be avoided with good forward planning before installation of your stove. An experienced Chimney Sweep can help with the recognition/diagnosis of these issues and it it better to seek advice sooner rather than later as solutions may become more expensive later on.

Conclusion

So, after examining the causes of tar build up in stoves, chimneys and liners we must consider the costs involved, both to the customer and to the environment. Burning the correct type of fuel in a modern efficient stove can be one of the cleanest ways of heating your home providing it is done correctly with fuel from a sustainable source. All wood will release the same amount of carbon dioxide (CO2) into the environment once the tree is dead, that it took in during its lifetime. Burning your logs in an efficient manner will ensure that other pollutants are burned off and all that is released into the environment is this same amount of CO2 meaning that burning seasoned wood efficiently can be considered a carbon neutral form of heating! Of course other factors such as transportation and energy needed to kiln dry will come into the debate.

If you find that you get a build up of tar then you should now be able to understand the possible reasons why and the remedies available to you. Of course to remove the tar you will need the services of a qualified, registered Chimney Sweep as it is important to do it in such a way as to avoid damage to your chimney/flue. Sometimes this can even require expensive chemical treatments so it is now clear why you should do your part to avoid this problem to begin with. So, remember to get your chimney swept regularly and always seek advice if in doubt!

Andy Smith is a Lancashire based Chimney Sweep registered with the National Association of Chimney Sweeps (NACS). Smiths Chimney Sweeping serves most areas of Lancashire and the North West including; Chorley, Bolton, Wigan and Blackburn.

Generally, it’s cheaper and longer lasting than wood. I also find the heat from smokeless that bit more intense. But like any fuel, smokeless needs to be used properly in order to get the best from it.

Here’s five common issues/hints and tips with smokeless fuel:

Always Clear The Grate and Ashpan Before Lighting a Smokeless Fire

Mineral fuels such as coal need air from below to combust, so it’s important air can flow through the fire. Restricting the air flow will either result in the fire not catching at all, or it will burn at a really poor rate and you’ll get no heat from it.

Never Mix Smokeless and Wood Logs

This is a really common mistake which people make. There’s a few reasons why it’s a bad idea.

Firstly, as mentioned above, smokeless needs air from below the grate to combust. However, wood only needs air from above. So burning the two in the same fire is highly inefficient for both sets of fuels.

Also, and this is becoming more and more common, mixing the fuels can prompt premature liner failure. The reason is that the moisture from the wood (even dry wood has some moisture content) combines with the sulphur in the smokeless fuel to create an acid which attacks flues, particularly stainless steel liners.

You CAN of course use dry kindling wood to start a smokeless fire, but I strongly advise against using wood as a main fuel on a smokeless fire. My advice is stick to just one fuel type (either smokeless or logs) in a fire and burn it hot.

Never Burn Wet or Damp Smokeless Coal

Even though it comes bagged up, most smokeless ovals are left out in fuel producers and merchants’ yards in all weathers before being bagged. And even if they’re not left out, the coal can ‘sweat’ in plastic bags.

Putting wet smokeless (or any fuel come to that) on a fire will cause it to burn at really low rate. The moisture from the fuel will go up the flue and cause damage, particularly if you have a stainless steel liner. It also causes a really unpleasant ‘goo’ in the stove and on top of your stove’s baffle/throat plate.

The best way round this is to invest in a good coal bunker which allows your smokeless coal to air dry. Even if you buy your smokeless in bags, tip them in to a bunker before using them.

Never Slumber Smokeless Fuel or Burn It Overnight

There’s always a temptation to slow down a fire, either in an attempt to make it last longer or in order to reduce the heat, by turning down the air controls on your stove. Don’t do it.

The fuel will still burn, but more smoke and moisture will be emitted. This is not only bad for the environment (and make you Public Enemy Number One among your neighbours) it will ruin your flue. Moreover, you’ll get no heat out of it so you will be wasting your money.

If you’re finding the heat too much, open a door or a window. It’s much better for the stove and flue. As for the old excuse of people liking the fire to still be ‘in’ when they wake up, it’s just as simple to clear the grate, put some fuel on and start a fresh fire.

Not All Coal Is Equal – Check Before You Spend

Some smokeless coals are not approved for use in Smoke Control Areas or in multi fuel stoves. Also, never ever burn traditional housecoal in a multi fuel stove. This type of fuel can – at the time of writing – only be used on open fires in areas where there are no restrictions on burning. It also creates a heck of a lot of soot and, because of the amount of dust it contains and the gases it produces it can actually cause a ‘flash’ and possibly shatter stove glass.

Conclusion: My Thoughts on Smokeless Fuel

Smokeless fuel has had a bit of a bad press among sweeps in the past few years. This is largely because of the way people have burnt and and we are seeing the consequences; damaged liners. It’s true that the type of soot produced by smokeless is slightly more acidic than wood soot, so of course that in turn would make it slightly more corrosive. It is also a fossil fuel so not as great for the environment as seasoned wood. But I have customers who have burnt smokeless fuel for years, largely because they’ve been shown how to use it correctly. And that’s the nub of it; used correctly in an appliance which has been properly fitted and regularly maintained/swept, smokeless fuel can really work for you.

Smiths Chimney sweeping is a National Association of Chimney Sweeps (NACS) registered company serving Chorley, Wigan, Bolton and surrounding areas. To Book Now  Call 07504 745787.