This section covers the issues involved in running your stove safely and efficiently.
The techniques used to burn wood are quite different to those used for burning solid fuel. To get the best results, you must have the right stove for the job, set it up correctly – and run it in accordance with certain basic principles. To do otherwise invites disappointment and may even create a fire hazard.
The wrong way to burn wood in a stove
Bad technique can boost your fuel consumption and burn out grate bars and deflector plates. It can even burn out the stove itself and create a major fire hazard. Keep an eye open for the warning signs, all listed here.
The air-supply to a stove should be controlled to produce a mild brightening of the embers and a nice gentle rolling flame. If the stove is obviously roaring away then you are flooding it with cold air which is carrying most of the heat straight up the chimney. This is a mistake nearly everyone makes when they first buy a stove – particularly if they have bought one too small for the job in hand. There is a strong instinct to produce a mass of crackling flames much as you would in an open hearth – and an even stronger instinct to believe that the more flames you produce the more heat the stove will produce.
To an extent this is true, but look at the diagram. The deflector plate is glowing bright cherry red, as is the flue connector. And the chances are that the bottom section of the chimney will fail soon under the assault of constant ‘combustion-chamber’ temperatures. Meanwhile there is no charcoal in the fire-box, and no prospect of any being created. The logs are burning straight onto open grate bars so that as soon as glowing embers are produced they fall through into the ashpan which is emptied at regular intervals in the mistaken belief that this is ‘correct procedure.’ It is for solid fuel, but not for wood.
If you suffer any of the problems highlighted in this section, click here to remind yourself how things should be!
The dangers of slow burning wood in a stove
Wood is an excellent clean-burning, smokeless fuel when burned at high temperatures. It is a diabolical polluting fuel when burned at low temperatures. Worst of all it becomes a fire hazard when green or unseasoned logs are ‘cooked’ in a hot stove for hours at a time. In such conditions highly flammable tars and creosotes are produced that stick to the flues like glue and are almost impossible to remove.
There is a special temptation to slumber a stove when you want to wake up to a warm house – or if you are away all day and want to return to a home at a comfortable temperature. In theory a woodburning stove may be able to deliver what you want. In practice it is all to easy to set up the conditions shown here. As the hours pass, the temperature in the stove drop steadily and the production of smoke and tars increases. As when wet grass is dropped onto a low bonfire there just isn’t enough heat to burn up the fuel and a pall of dense smoke is produced. By the time you return to the appliance it is barely warm, the glass is as black as pitch (it is pitch – literally!) and there is often an unpleasant, sour smell hanging around that catches your throat.
A stove’s tolerance to being slow-burned depends on several factors. If your wood is bone dry and the chimney has been fitted with a low-mass liner back-filled with insulating material you may be able to turn down the heat for quite lengthy periods without incurring any penalty, providing you have got the firebox up to a good temperature. But this will be much harder to do if the stove is too big for the job in the first place – or if it is equipped with a high-output central-heating boiler. (All boilers reduce the fire-box temperatures to a degree, but a worst-case scenario is a high-output boiler served by an out-of-control pump that circulates cold water through the appliance. As a matter of course a low-level thermostat should be fitted that disconnects the pump when the water temperature falls below 50º C.)
To sum up, a “dry” stove (i.e., no boiler fitted) burning fully seasoned logs in a warm (well insulated) chimney may tolerate fairly long, slow burns. A stove equipped with a central-heating boiler, fuelled on wet wood and connected to a cold chimney can never safely be run slow at all. If you are ever caught in this situation the safest bet is to switch to wood briquettes or smokeless fuel (assuming the stove is of ‘multifuel’ design) without delay.
The right way to burn solid fuel in a stove
Many stoves on the market are designed with a ‘multifuel facility’. This offers you the option of burning wood or solid fuel according to availability – an attractive proposition. However the two fuels are quite different from each other and to get the best results you need to set up the stove correctly and alter your technique. This section explains the principles involved.
Choosing the best solid fuel for your stove can be quite tricky and you may have to experiment to get the best results. Household (“bituminous”) coal has been band. It produces great volumes of soot and a long hot flame that can burn out deflector plates and flues. Anthracite can congeal and clog the grate bars – and some grades produce such intense heat that they may burn out grate bars rapidly. In general the most satisfactory fuels are the man-made ‘smokeless’ grades. The lumps are often ovoid (“egg-shaped”) and brands like Phurnicite and Homefire are well worth experimenting with.
It is vital to burn solid fuel straight onto an open grate and the grate must be riddled and ash removed at regular intervals. The air supply is generally controlled by a valve serving the ashpit so that a cool stream of air is directed upwards into the heart of the fire in a way that helps prevent the grate bars from over-heating.
Solid fuel likes to burn in a firebox that is narrow and deep and larger multifuel stoves don’t always provide ideal conditions – you end up with shallow coals scattered across the full width of the firebox. Mixing wood with smokeless fuel is to be avoided as under some conditions they precipitate supherous acid which will of course shorten the life of metal components (particularly boilers).
Smokeless fuel is far superior to wood as a central-heating fuel in domestic appliances. Given its short flame and its intense radiant output it can ‘punch’ heat straight into your boiler at a rate that will keep your radiators spanking hot for hours at a stretch. Wood just isn’t up to this task except when fed to a much bulkier specialised appliance typically located in a utility room or outhouse or if you have a baffle type boiler which hangs above the firebox.
For these reasons, you should budget to burn mainly smokeless fuel in the depths of winter if your stove is heavily boilered.
One last thing to note is that solid fuel is extremely sluggish in its response compared to wood. It takes longer to light, longer to deliver its full output – and longer to cool down. It is also much less forgiving than wood when burned at low output – often, it simply goes out.
The wrong way to burn solid fuel in a stove
You may not intend to misuse and abuse your stove, but you can do so unwittingly – and the cost can be high. Soaring fuel bills and a constant need to replace grate bars and deflector plate are just some of the ills that will plague you.
Three things have gone badly wrong in the above scenario;-
• Household (“bituminous”) coal is being burned. It produces a great deal of soot and in a closed stove there simply is not enough air passing through the fire-box to carry the soot up the chimney, so that the flueways get clogged and frequent chimney fires can be expected.
• So much air is being admitted that the effect is of an open fire being burned in a closed box. You can see the result. When you fuel a stove with household coal and admit large volumes of air you get exceptionally long flames. The deflector plate and flue collar are both red hot and will burn out rapidly. Meanwhile most of the heat is disappearing up the chimney and the in-rush of cold air is chilling the base of the stove and causing uneven expansion in the metalwork. Running your stove in this manner will cause doors and panels to warp and shorten the life of the appliance.
• Ash has built up in the ash-pan. As a result the grate bars are trapped in a bed of red hot ash close to the temperature at which they were cast in the iron foundry. Naturally they will distort and burn out rapidly under these conditions.
The impact of chimney construction and lining
Soot particles travelling up a chimney from an open fire. Note that they are spaced well apart because they have been diluted by the large volume of air sucked into the chimney. The hot flue gases remain hot to the top of the chimney and also heat up the chimney itself.
Cracks in liner caused by chimney fire allow discoloured condensate to penetrate masonry and plasterwork.
Soot particles travel up a chimney from a closed stove. Because the smoke is not diluted much, the particles are packed together at high density. Also the low volume of slow-moving flue-gases get chilled by the heavy mass of masonry in the chimney, causing creosotes to precipitate on the way up and create a major fire hazard.
Here the soot particles remain tightly packed as before but now the flue-gases stay hot to the top of the chimney because they are contained within a low-mass flexible liner back-filled with insulating material. The higher temperatures eliminate or drastically reduce precipitation of flammable tars and creosotes.