Greenfires Chimney and Stove Services

Wet wood is probably the biggest cause of problems in stoves and chimneys. The moisture in the wood has to be driven off before the log can burn properly, and this uses a great deal of the energy that the log contains - so the wetter the wood you throw in the stove, the less heat you'll get out of it. The problems don't stop there - all that moisture is contained in the smoke and steam that goes up the chimney - and because there's very little draught going up the chimney from a stove compared to an open fire, that moisture along with tars and creosote in the smoke is likely to condense on the cooler walls of the chimney itself - particularly towards the top where the chimney is coolest. Eventually these deposits can eat their way through the mortar joints of the chimney, and appear as stains on the inside walls of the house, particularly in upstairs rooms - often accompanied by a tarry smell. This can be difficult and expensive to rectify.

Those deposits of tar and creosote can also build up and greatly increase the chances of having a chimney fire. This can be a frightening experience, as well as causing structural damage to your property as they can burn at over 1000 degrees Celsius.

Another possibility is that the deposits can build up to an extent where the chimney is almost completely blocked. This can lead to carbon monoxide leaking into your home, and sadly we read in the papers all too often about people losing their lives due to being overcome by fumes from badly maintained chimneys.

These problems and risks can be eliminated almost entirely by having the chimney swept regularly, and by using good practice in the way you operate your stove, and in the fuel you use. Logs going in the stove should have a moisture content of 25% or less - the lower the better. Moisture can be tested using a small electronic meter, which you can pick up for around £20. To test the wood, you should split a few pieces, and then push the meter probes into the wood on the freshly split surface - NOT into the cut ends of the log.

These two pictures show how deposits of tar and soot can build up in your chimney (thanks to Craig Forster Chimney Sweep for the pics)

Just for comparison, here are the moisture levels for various fuels. Remember that less moisture means more heat output for any given weight of fuel.

Fresh cut logs - up to around 60% moisture depending on species and time of year (winter cut trees have much lower moisture content)
Average air dried logs - around 25%
Well seasoned logs - 19% - 22%
Kiln dried logs - around 12% - 15% (these need to be kept sealed until they are used or they will reabsorb moisture from the air)
Firewood briquettes - 8%

If you are running your stove correctly and using good quality dry fuel, your glass should stay pretty clean. Some of the cheaper imported stoves tend not to be so good at this incidentally. Anyway - if your stove glass does need a bit of a clean up, you can buy a proprietory stove glass cleaning fluid, which we can supply. This is simply sprayed onto the glass, left for a minute or two, and then wiped off with a cloth or paper towel.

If you are burning only wood, then you can damp a bit of newspaper and dip it in the ash in the stove. This also does a good job of removing staining - but only if you only burn wood. Ash from smokeless fuels is a lot more abrasive and will scratch the glass!

There is no problem at all with buying unseasoned logs, as long as you're prepared to sit on them for a while until they are dry enough for the stove. There is no hard and fast rule about how long this will take - it varies widely depending on the species of timber, the size of the logs and the conditions they are stored in. Airflow through the logs is the most important thing. Logs piled up in a heap in a closed garage or shed are more likely to go mouldy than dry out. They are much better stored outside in a log store with an open front and open or slatted sides, where the air can get through the whole stack to dry it out. If you don't have a log store, then the best bet is to stack them outside on pallets to keep them off the floor and allow air to circulate underneath them. It's also not a bad idea to put a tarp over the top to keep the worst of the rain off, but leave the sides open to the wind.

We tend to be pretty conservative with our logpiles here in the UK - in parts of Europe, where just about everyone has a woodburner, they get a little more creative!!

You may not be aware that an open fire can actually cool your house down overall!

An open fire sends up to 85% of the heat it produces straight up the chimney, along with a huge amount of air - around 5 cubic metres a minute. This air has to be replaced, and so the same amount of air is drawn into your home from the outside - under doors, around window frames and so on. This can mean that your central heating system if you have one, is working overtime to try and keep up with all the cold air coming in.

A modern stove by comparison puts the majority of the heat it produces into the room, and a much smaller amount of air goes up the chimney. Many of our customers say that they are saving a fortune on their gas bills as they can turn the heating down. By leaving internal doors open, the heat from the stove can circulate around the house meaning that the radiators have a lot less work to do.

The basic difference between a multi-fuel stove and a pure woodburning stove is that the woodburner generally has no grate fitted. This is because wood burns best sitting on a bed of ash, getting it's air supply from above. Smokeless fuels prefer their air from below coming up through the firebed - and so multi-fuel stoves are fitted with a grate for the fuel to sit on.

Many people go for the multi fuel option, and to be honest, although we burn nothing but wood here, using some smokeless fuel from time to time can help keep the chimney clean if you're burning wood that isn't top notch. It's worth remembering though that you shouldn't burn wood and smokeless at the same time, as the sulphur compounds from the smokeless can react with the moisture coming off the wood to produce sulphuric acid. Okay, it's not going to be strong enough to take your fingers off or anything - but it can reduce the life of your flue liner, or damage the mortar and brickwork of your chimney. If you've bought firewood that won't stay alight on it's own, then you really shouldn't be trying to make it go by using smokeless as well!

Housecoal is not generally thought to be a suitable fuel for use in a stove. It's dirty stuff and we'd be much better off avoiding it!

We've seen a number of instances of woodcoal being packaged and promoted as an ecologically friendly alternative to traditional housecoal. The variety usually found in the UK is "Union" brand and comes from Germany in the form of small briquettes with the UNION name embossed in the moulding.

Woodcoal is an intermediary between peat and coal, and is reckoned to be one of the dirtiest solid fuels you can burn. Power stations running on this stuff produce more CO2 emissions than any other form of power generation, and there are also big concerns about the environmental impact of the huge opencast mining operations in Germany and Australia that produce the woodcoal.

More reading if you're interested at:

http://www.thelocal.de/sci-tech/20081015-14927.html

http://www.greenlivingtips.com/blogs/436/Australias-brown-coal-shame.html

The various chimney sweeps trade organisations recommend the following frequencies for sweeping chimneys used with various types of fuel.

Smokeless fuel - at least once a year

Coal - twice a year

Oil and gas - once a year

Wood - quarterly when in use

In practice, many people using good quality firewood or briquettes, and employing good practices in the use of their stove can have their chimneys swept less frequently. We can get a pretty good idea of the fuel you're using when we sweep, and advise on how soon you should have us visit again.