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The most common problem that we see when customers say to us that the glass on their stove is getting black is that the wood that they are burning is too wet.

Every log that you put on your fire has an energy value known as Calorific value (a maximum amount of energy that burning that log will produce). Wet logs have just as much potential as dry logs but most of the energy created by burning a wet log is wasted. The energy is used to heat the water in to steam which goes up the chimney rather than radiated heat that heats your room.

Here is what the forestry commission has to say about wet logs:

The moisture content of wood has by far the greatest effect on calorific value. Any water in the timber has to boil away before the wood will burn, and this will reduce the net energy released as useful heat (as opposed to steam up the chimney). If you can get them to light at all, logs that aren’t dry will result in a fire that smoulders and creates lots of tars and smoke. These tars can be corrosive, potentially damaging the lining of the flue and increasing the danger of a chimney fire. Wet logs will tend to blacken glass in stoves even if the stove is designed to keep the glass clean. Well seasoned logs can have approximately twice the Calorific Value of green logs. You should always take care to burn only dried (seasoned) wood, either by buying it dry, or by buying green logs and drying them yourself. Radial cracks and bark that comes off easily suggests well-seasoned wood.

If you are not sure how dry your logs are then use a moisture meter (or bring one in to the showroom and we will test it for you). You should also be able to tell by checking the wood – wet logs are heavy, dry logs are light with radial cracks and bark that is splitting from the wood. All the wood you burn should have a moisture content of less than 20%. If you are seasoning your own logs they need to be stored in a well ventilated area for at least 18 months (see the wood guide for more information). If you are buying logs in we don't recommend getting logs from garage forecourts – they are very often too wet. Why not speak to Walkers logs about getting a delivery of Kiln dried logs or get a couple of boxes from us?

A common misconception is that burning wet logs mean that the logs last longer. This is a false economy. You will use more logs to get the room to temperature and they burn colder making the flue full of residue. Far better to use dry logs, turn the air down low so that they are really efficient, keep the glass clean and enjoy watching the rolling flames of secondary burn. You'll be up and down out of your chair less poking the fire to keep it going and you will save yourself a lot of money in fuel as your room will heat more quickly thus using less logs per fire.

If you are burning kiln dried logs and the glass is still blacking up then it is likely that the air controls on the stove aren't being used to their best effect. We do say it always takes a while to get used to your particular stove but some basic pointers can be seen on the blog post “How to light a wood fire”.

One more hint. Your stove will probably have an air wash – if you are turning all the air vents off on the fire to try and keep the fire in over night the stove will almost certainly blacken up. The air wash is exactly that -no air, no wash. We don't recommend keeping stoves in overnight – as the chimney cools from the top down the residues from the fire find it harder and harder to escape the chimney – this can cause extra deposits in the flue which can lead to chimney fires. These days most stoves are so easy to light that you would do better to bank it up with the air still open but on low at bedtime and in the morning re light from the warm embers – it's best to do this with wood as coal has to be riddled to keep it burning.


Don't forget to arrange for chimney sweep to service your chimney at least once a year in an active chimney. It may require more frequent sweeping depending on usage and fuel being burnt. Ask the staff at our showroom or your chimney sweep for more guidance.