Never try to “slumber” your stove for long periods/overnight with the air controls closed off. Loading up the average stove to slumber for a long period can easily produce more than a kilo of tiny damaging particles which then pass out the top of your chimney and into the air we all breathe not to mention the deposits that will accumulate in your flue.
The Science of Burning
Logs when burnt contain 70-80% “volatile hydrocarbons” and 15-18% fixed carbons. Volatile hydrocarbon compounds take the form of tars, creosote, and resins etc. When we see flames coming from wood, it is the volatile gasses that are burning.
If the fire is not hot enough these volatile vapours are still given off but are not completely burned in the appliance, they escape into the chimney. If the chimney is cool, some of these vapours will condense and solidify on to the inside of the chimney. In some chimneys they solidify to form the tarry deposits or creosote glaze.
When we see wood and embers glowing, it is the fixed carbon that is burning.
It is important to use dry wood. Aim for a 20% moisture content or less. If you are buying logs for immediate use, then tell your supplier you want to use them straight away and you want logs with a 20% moisture content or less. Do not settle for less. Alternatively, look out for the Ready to Burn logo for reassurance that the logs are dry and sustainably sourced.
Poor Burning Habits
Constant smoke from the chimney – the chimney will smoke when first lit and perhaps when refuelling but otherwise there should be no smoke – smoke is simply unburned fuel, loaded with damaging particles
Unburned wood or charcoal left after the stove goes out
If you would like to discuss your appliance fuel burning requirements or anything to do with your chimney, please do not hesitate to get in touch.
Types of Soot
(Type 1 Creosotes) - Ideal
Powdery soot is produced when fuel burns well, wood will produce powdery soot partly because it has plenty of air and partly because it’s seasoned, by that I mean a moisture content of less than 20%. First-degree creosote is the easiest to remove from your chimney and you should have at least an annual sweep and service.
Burning smokeless fuel will also produce fine soot, this requires at least an annual sweep but I will advise you on your certificate.
(Type 2 Creosotes) - Not So Good
Second-degree creosote or crunchy deposits are more complicated to remove. This type of creosote builds up and will be removed as lumps, which when crushed in your hand, easily crumble.
Stage two deposits can be removed effectively by a powered system. But they will have formed due to either wet wood being burnt or more commonly poor combustion, due to air starvation, especially if the stove is throttled back (called slumbering). These type of deposits require at least twice yearly sweeping as they are more likely to be a fire risk.
Glassy (Type 3 Creosotes)
- Hard to Remove
The most problematic type of creosote is Stage Three or third degree creosote. Cleaning this kind of creosote from your chimney is very difficult, and when you look up the flue it may look like black glass.
Stage three creosote is highly concentrated fuel as a coating of tar has run down the inside of your chimney. This kind of creosote can form a thick layer as it becomes hardened. More aggressive sweeping methods may be required.These type of deposits require at least twice yearly sweeping.
Type 3 deposits are more likely to cause a chimney fires, hence the increased vigilance and getting the flue swept and changing your burning habits.
On What Your Fire Needs
All fuels like air to burn and give their best heat output.
Wood - likes to burn on bed of ash and with air from above - so bottom air control should be closed.
Coal - likes to be riddled and get its air from underneath - so top air control should be closed.
Fuel -In a stove smokeless fuels should be used, never house coal as it is too corrosive.
Wood should have a moisture content of less than 20% - ask me to test your wood with my moisture meter.
All fires need air to combust - building regulations stipulate the requirements for air - ask me for details.
Carbon Monoxide - you must protect yourself if you have an appliance that burns a fossil fuel. I keep Carbon Monoxide detectors on the van - they do save lives.