Fuel for Stoves and Open Fires

When considering what fuel for stoves and open fires, please keep in mind that it’s not as simple as it first appears.  You would be forgiven for thinking that it just simply boils down to whether you should burn wood or coal.

However, bear in mind that Fire and Rescue Services state that burning wet and unseasoned wood is one of the top causes of chimney fires, second only to infrequent chimney cleaning.

Not only does your choice in fuel affect the risk of chimney fires in your home but in some cases picking the wrong fuel can actually damage your chimney liner – requiring replacement typically within as little as 5 years.  Not the 20-30 years that your chimney liner should be lasting you.

So, let’s get into the few details you need to be aware of when picking solid fuel for stoves and open fireplaces.

Choosing the right fuel:

If you don’t live in a smoke controlled zone, the type of fuel you burn will be dependent on the type of appliance you have:

Appliance type                 Fuel

Open fireplace                  Kiln dried wood, seasoned wood, house coal & smokeless coal

Multi-fuel stove                Kiln dried wood, seasoned wood & smokeless coal

Wood burning stove        Kiln dried wood, seasoned wood

Please note the type of fuel you can burn will also depend on the grade of liner you have installed.  If you have a grade 316 stainless steel liner then you cannot burn smokeless coal.

Dangers of burning unsuitable fuel:

Burning wood that isn’t properly seasoned or kiln dried will create tar and creosote in your chimney.  This in turn acts as fuel for chimney fires putting yourself and your home at risk.

Burning smokeless coal on a grade 316 stainless steel liner will damage the liner and invalidate its warranty.

Do you live in a smoke controlled zone?

If you live in a smoke controlled zone you will need smokeless coal.  To check if you do live in one of these areas then your best bet is contacting your local council; most have a search facility on their website which will identify whether or not your home falls into a smoke controlled zone.

If your home does fall into the smoke controlled zone, then there are two questions you’ll need to know the answers to:

  • Is my stove DEFRA Approved?
  • What type of chimney liner do I have?

If you have a DEFRA Approved stove this means that you are allowed to burn smokeless coal and seasoned wood.  If you don’t have a DEFRA Approved stove or you have an open fireplace you are only allowed to burn smokeless coal.  If you don’t follow these guidelines you will be breaking the law.

It’s important that you know what type of liner you have as some liners are not suitable for burning smokeless coal.  You can find this information on the installation certificate or the data plate.  If it states a grade 316 stainless steel liner, then your liner is not suitable for burning smokeless coal.

What’s the difference between wet and dry wood?

When discussing the moisture levels of wood, there are typically two terms used; wet wood and dry wood.  The differentiating moisture level is 50% – wood with a moisture level of 50% or higher is defined as wet wood.  The optimum range of moisture in wood is 10%-20%, anything over 20% needs to season further.

What is seasoned wood?

Many people mistake the moisture content of wood to only relate to wetness of the wood from rain.  So therefore, the assumption is that if the wood is left somewhere to dry for a few months so it’s dry to the touch it’s ok to burn.  Unfortunately this isn’t the case and catches many people out.  The moisture content relates to the cells within the wood and the fact that those cells hold moisture.  The seasoning process enables those cells and sap to dry out.

Another area that catches people out is the length of time required for seasoning.  To properly season wood, once it has felled it needs to be left to season for 5-6 years before it can be safely burnt on your stove or fireplace.

Part seasoned wood which has been left to seasoned for 2-3 years can be purchased cheaper than fully seasoned wood but it is expected that you will leave it to season for a further 2-3 years before using it.  That’s why it’s cheaper than fully seasoned wood.

Many local log suppliers only season wood for 2 years and sell it as seasoned wood with no information on the requirements by the customer for further seasoning.  So make sure you’re aware of what you’re purchasing and when it’s safe to use as fuel.

Why does the moisture level of wood matter?

There are two main reasons why the moisture of wood matters when using it for fuel:

  1. The higher the moisture content, the more energy it takes for the fire to burn the moisture off. So when the wood is put on to the fire, the fire first needs to burn the moisture off before it can create heat coming back into the room.  This is why when you put a wet log on to the fire it can take a long time to set alight.  This is your biggest clue that you’re not burning seasoned enough wood.  The impact here is financially.  The more wet wood you have, the less heat comes back into your room which means you need to keep putting more wood on the fire.  People with well-seasoned or kiln dried wood will typically use less fuel and therefore have lower fuel bills.
  2. The second reason the moisture level matters is that burning fuel with a high moisture content will create creosote and tar. This creosote and tar is fairly lumpy and will build up which minimises the diameter of your flue restricting the pathway that removes smoke and carbon monoxide from your fireplace.  This means, if the blockage builds up enough, you’re risking carbon monoxide coming back into the room.  Another risk, is that the creosote and tar created from burning unseasoned wood, is lining the length of your flue which is the perfect fuel to get a chimney fire started and keep it going.

What’s kiln dried wood and how does it compare to seasoned wood?

Kiln dried wood is where a tree is felled and then put into a kiln to dry out the moisture levels.  Because of this kiln drying process it does make kiln dried wood slightly more expensive than seasoned wood however with kiln dried wood you can expect moisture levels of less than 20% (where as seasoned wood is less than 25%).  You can also expect to get 3 times as much heat output of a kiln dried log than an unseasoned log.  So, while the kiln dried wood may be slightly more expensive to purchase, it will last longer than unseasoned wood making it the clear choice to go with when purchasing wood – not only for the impact on your budget but also the fact it is the lowest risk to your chimney with regards to moisture level.

How can fuel damage chimney liners?

Typically, there are three ways in which the fuel you burn can damage your liner:

Firstly, burning smokeless coal on an unsuitable liner (such as stainless steel grade 316 liner), the chemicals in smokeless coal erode away at the stainless steel liner creating holes.

Secondly, the acid in soot attacks either your lining or the cement holding the bricks of your chimney together.  If you have a lot of tar and creosote stuck to the inside of your liner – not 100% of it can be removed by sweeping and the bits left over will erode your liner over time.

Thirdly, if you have a chimney fire which is typically due to not having the chimney swept regularly enough and burning un-seasoned wood, the damage that the fire does to the chimney will usually result in the chimney needing to go through various treatments to remove the creosote and then re-lining.  A chimney fire on a stainless steel liner will invalidate the warranty because of this damage that can be done at such high temperatures.

So, what’s the best fuel to burn?

Our advice is to stick with kiln dried wood – you’re guaranteed to have wood that has a moisture content that is less than 20%.  This guarantee simply cannot be applied to seasoned wood due to the process.

If you’re able to buy it in bulk, so either one cubic metre crate or two will result in best value for money.  The handy thing about buying it in crates is that it is delivered in the crate already packed.  Most local log suppliers will turn up with a loose load and empty it on to your driveway for you to pack yourself.  By purchasing it in crates it comes ready packed and is a lot less hassle for you.

If you’re in a smoke controlled zone and your appliance isn’t DEFRA Approved then you must burn smokeless coal.  But remember to check the grade of your liner for suitability.

As well as the kiln dried logs, having a selection of kindling and firelighters to get your fire started will be useful.  With kiln dried logs you’ll find you need a lot less kindling than you do with wood that has been part seasoned or even fully seasoned.  Kiln dried wood catches alight much quicker with less requirement from kindling.

 

If you’re looking for further information specific to appliance types, check out our following articles:

 

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Wight Initiatives Ltd,
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Cambridge, CB1 1AH
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Registered in the UK # 7725 203
VAT # 218 3459 04