Saturday, 2 January 2010

Wood burners - a way of life

Jane blogged that she is thinking about getting a wood burner; I was going to email some notes to her but I thought that I would blog them so that others can add comments about their own experiences. I have tried to give an idea of what living with a wood burner is like – I have not covered building regs, chimney design etc. It is a complex subject and badly installed wood burners can cause fires and carbon monoxide poisoning – so take expert advice before installing one. There is a technical discussion taking place at http://groups.google.co.uk/group/tn-two.
The most common mistake is to get too large a stove. Wood burners work best if they are burning dry wood vigorously – smouldering wood leads to tarred up chimneys (eventually chimney fires) and smoke that will annoy the neighbours. A large wood burner can emit more than 6kw which would rapidly turn the average living room into an oven. I have a small (4kw) stove and that keeps most of a 4 bed 1970’s house pretty warm, even on freezing day, burning just one small log at a time.

My first stove was a 1980 Hunter. I now realize that it was not a very good stove! It had double doors that did not fit tightly so it was not possible to control the burning rate by use of the air inlet controls, you had to use a flue damper and this had to be opened every time the doors were opened – otherwise the room filled with smoke. It was lined with stove bricks and had a second skin designed to give convected heat. This had the safety advantage of not having such a hot surface (we had young children) but meant that no useful heat was produced for about an hour! (Even with a radiant type of stove it will take 20 minutes from first lighting before you get useful heat). There was no airwash system so the glass in the doors was always black.

I also had a multifuel (wood, coal, peat, dried dung etc) boiler – basically a large water jacket with a firebox in the middle. This was connected to the central heating and the air inlet was regulated by the water temperature. The main problem was that it would blaze away when the pump was running but once the pump stopped the air inlet would shut down and starve the hot fire of air until enough air seeped in to cause a backdraft (see http://en.wikipedia.org/wiki/Backdraft) – this caused the top plate of the boiler to lift an inch into the air and emit a flash of flame with a loud ‘whooossh’, which upset the cat dreadfully. All wood burners will do something similar – though not as dramatically! There will be a ‘whoosh’ and some foul smelling smoke will puff out into the room. The boiler worked OK provided that you were there all the time to keep an eye on it.

There are two stoves in my current house – an extended 1970s dormer bungalow, as well insulated as I can manage and with many south facing windows. Externally the stoves are similar sizes and both would be described as small – about 4kw. However there are significant differences due to their construction.

One stove is an Aarrow mulifuel stove, it came with the house and is probably 30 years old but still in very good condition. It has an adjustable grate that can be closed to burn wood or opened to burn coal (wood burns best on a bed of ash, so always leave some in the stove, coal needs air to be drawn through the grate). The stove is lined with fire bricks and has a single glass door with an air inlet above which keeps the glass very clean. The stove works well but because of the grate and brick lining the firebox is small and I have to cut the wood up small and feed the stove every hour with hardwood or more frequently with softwood. The stove is in my office so I can look after it easily. The room is about 4m * 4m and I have to keep the door wide open to the rest of the house or I would cook in minutes, event with the stove on tickover. A lot of heat goes up the stairs, so on a cold day my office is about 23c, the upstairs rooms about 22c and the other downstairs rooms about 20c. The lip to the firebox is low and ash and hot embers fall out most times that I open the door, so I need at least a 35cm hearth. All wood will emit sparks (pine is worst) and some sparks will occur when the door is open. So I have holes in several fleeces and marks on the carpets. Natural fibres are less likely to burn, man made fibres melt as soon as a spark lands. A spark once shot across the room and it was some time before I found it smouldering behind a chair! The ashpan under the grate is no use when burning wood. The stove is connected to a metal flue that goes through a cupboard in the bedroom above and out through the roof. It is a cheap Spanish make and is OK but I’m surprised how hot the outside gets.

The other stove is Yeoman Exmoor. This a fairly cheap stove that only burns wood and is unlined, so the firebox and door are much bigger – it takes bigger logs and can be loaded with 3 times the wood that the Aarrow will take – hardwood embers will still be glowing in the morning. The design is good, the door is airtight and the three air controls all work well. It has air inlets at the base of the fire bed that make it easy to get a fire going – less effort than puffing! Much less ash falls out. Once the fire is lit the air controls have to be adjusted so that the fire is burning brightly but not too vigorously – otherwise things get very hot! The air adjustment is quite delicate and has to be adjusted as the chimney (brick with clay pot liner) warms up. The adjustment will be effected by wind and temperature outside. I have to use the poker point from time to time to stop the tertiary air inlets from getting blocked.

Because this stove has no brick lining it emits a lot of radiant heat – anything within 2m gets very hot. The rendering behind and beside the stove is cracked. Both my stoves are next to internal brick walls, these heat up and transmit heat to the next room – they can stay warm for a day after the stove has gone out. A lot of modern houses have stud partition walls – these would need protection from the heat.

Some ash gets out when you open the stove door and some gets into the air when you clean out the stove. Some dirt drops of the wood that I bring in to burn. Spiders and hibernating wasps make their homes in the wood and these escape into the house. After cutting and chopping wood I am covered in sawdust! Owning a wood burner leads to more housework!

Wood smoke does smell – your neighbours may or may not find it pleasant! The picture shows the 2 flues on my house and our neighbour’s chimney. There are no houses opposite or behind us. We smell his woodburner when in our garden and I’m sure that he smells ours – depending on wind direction.

Wood is best felled in the winter when there is little sap and then needs to dry out for the summer before it is dry enough to burn. It is best to split the wood before it dries out – this also helps it dry better. The picture shows a heap of oak that I rescued recently – this should last us most of next winter (I run a business from home so have to use some oil in the morning to get the office warm enough for the staff – or I could get up very early and light the stove). We light a fire every day and use about 6 dustbins of kindling – mainly twigs pruned from trees in the garden. This all takes a lot of storage space!

Don’t try and split wood with a felling axe – you need a wedge shaped axe like in the picture, this one has a step in the blade to stop it sticking and is asymmetrical so that it twists in the wood. Or you can buy wood ready split and dried – make sure it has been cut small enough for your stove. Ash from the fire can be spread thinly around the garden as a nutrient but too much makes the soil ‘sticky’.

Owning a wood burner is a lot more work than having a gas boiler in a cupboard. If you enjoy the process of collecting and preparing your own fuel and you are methodical enough to make sure that the stove is burning properly then you will enjoy the process. If you find it all a chore then it could be an expensive/dangerous white elephant. I suggest that before buying a stove you visit a friend who owns one and spend an afternoon splitting and stacking wood, cleaning out the ash, lighting the fire and tending to it.

Please add your own comments.

13 comments:

  1. Charlotte Du Cann2 January 2010 12:44

    Dear John, Great post! Do you have any thoughts on what kind of wood burns best? We've used birch, hornbeam, oak and ash mostly, but out foraging I gather all and every kind, especially for kindling. Pine is spitty as you say but the needles and cones are great for getting the fires started, as are dead gorse and heather. Nice too to burn fragrant wood from the garden as a start up - rosemary, bay, apple twigs etc. Woodsmoke has to be one of the most welcoming smells in the world, especially on a frosty night.
    Warm wishes,
    Charlotte

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  2. The well known poem below is pretty accurate. I had some willow once that rotted before it had dried out and some wych elm that was impossible to split (which is why it was used to make the hubs of cart wheels) and useless to burn. The hardwoods are good once the fire is going but softwoods are useful for lighting the fire.
    John

    Logs to burn! Logs to burn!
    Logs to save the coal a turn!
    Here’s a word to make you wise
    When you hear the woodsman’s cries.

    Beech wood fires burn bright and clear,
    Hornbeam blazes too’
    If the logs are kept a year
    To season through and through.

    Oak logs will warm you well
    If they are old and dry.
    Larch logs of the pine smell
    But the sparks will fly.

    Pine is good and so is Yew
    For warmth through winter days,
    But poplar and the willow too
    Take long to dry or blaze.

    Birch logs will burn too fast,
    Alder scarce at all,
    Chestnut logs are good to last
    If cut in the fall

    Holly logs will burn like wax –
    You should burn them green.
    Elm logs like a smouldering flax,
    No flames to be seen.

    Pear logs and Apple logs
    They will scent a room,
    Cheery logs across the dogs
    Smell like flowers in bloom.

    But Ash logs all smooth and grey,
    Burn them green or old,
    Buy up all that come your way
    They’re worth their weight in Gold!

    *Elder, sweet chestnut, cedar, hemlock, balsam, spruce and the pines all spit hot cinders into the air.

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  3. Just found these links -
    http://www.whatstove.co.uk/
    http://en.tigchelkachels.nl/
    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1404

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  4. I grew up with wood burners and remember all the nice things about them- the lovely smell, the crackling sounds and the cosiness you can't get with anything else. And I also remember lugging logs around till it feels like your back will break, and the challenge of trying to coax a sulky flame into life on s freezing winters morning!

    We have just had our chimney swept ready to use the wood burner that's sat inert in our living room since we moved in two years ago. However it turns out that the chimney is completely unlined which I gather is either at best not good and at worst potentially dangerous, so we're now looking into that. Despite the setbacks we're really excited about getting up and running.

    The thing that concerns me the most however is the prospect of having a regular and sustainable source of wood. If everyone in Norwich decided to switch off the central heating and install wood burners, there would surely not be enough wood locally to satisfy that demand? Lots of people, including me, have talked about foraging for twigs or unwanted wood, but if ten thousand people suddenly started doing that it would be mayhem. Soon enough people would be poaching trees! Even if we were all insulated to the hilt, we'd still need a LOT of wood. The only answer may be to plan now for our wood needs in the next decade. Does anyone know of a local sustainable wood source to satisfy the needs of a sizeable proportion of Norwich's population?

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  5. helenofnorwich3 January 2010 20:02

    this is very interesting. i love woodburners but have never had anything to do with actually maintaining them. it has made me think twice. I might just replace my gas boiler so it is more efficient.
    helenofnorwich

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  6. Jon is correct that if every one installed a woodburner there would be a wood shortage. However at the moment the lack of market for wood means that a lot is going to waste. I have obtained free wood for the last 8 years entirely from within the village. Many tonnes that I could not store went to waste. Of course I could only get this wood by using a car to transport it and a chain saw to cut up the wood. There is massive scope to develop a local wood supply industry.

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  7. If this is the case, is there anything we in Transition could do to support one? I also heard the other day on Radio Norwich an add for a company (can't remember the name) who supply "logs" made from sawdust & offcuts from their (presumably) furniture factory.

    On a related point, I was having a conversation with someone who challenged me that using a petrol-driven chainsaw to chop / cut up wood cancelled out any environmental benefits of burning wood. Therm for therm, went the argument, it would be better to burn the petrol / use it to generate electricity. Is there any research or view on this?

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  8. I use less than 5l of petrol to saw (crosscut)a year's supply of wood that saves at least 1000l of heating oil. Of course I also split the wood by hand - anyone who tried to rip down the grain with a chainsaw would use a lot more petrol! But not anywhere near 1000l.

    If someone has time and energy then they could look at exploiting the copicing of woods such as Ashwelthorpe - at present volunteers cut huge piles of wood and then just burn it in bonfires!

    About 50% of stuff going to landfill is classified as timber products! Eastex often has offers of lorry loads of ex packaging wood.

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  9. I should also have pointed out that had I not rescued and sawn up my recent haul that it would all have been chipped and transported out of the village - using a lot more fuel than my chain saw - with no payback!

    The saw is now 30 years old and has only needed a few apare parts - it should be good for another 20 years. The stoves could last a lifetime and the metal then be recycled. So a good use of resources in my opinion.

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  10. I am a bit of a wood nut at home and work

    Over the last 25 years I have installed and operated two wood stoves coupled to small back boilers and the gas central heating systems to do domestic hot water or a couple of radiators

    In summer I used to have higher gas bills than winter as I would run the stove when it got cold and do most of the heating and hot water. Last year I installed a secondhand solar hot water system so should have reduced further.

    My Clearview Wood stove is great but it does take a lot of work to forge, cut, stack and bring in wood but I haven't ever bought wood and have very low gas bills.

    We must plant and manage more woodland but have found via my work at UEA that most farmers don't manage woodland as it is not cost effective as the isn't the commercial outlet for the thinings etc.

    At UEA I am the project director for the Biomass Energy Centre a plant that will provide 35% of this campuses heat and electricity via gasification of wood chips.
    This 1.5MW electrical 2MW heat Combined Heat and Power plant will hopefully use local sawmill by product from the two sawmills just above Norwich. Currently they produce many times what we need and it is trucked down to Slough powerstation or into the Midlands.

    Once we have sorted this innovative plant it could be the way forward for a number of cities to provide local renewable electricity and heat via district hotwater systems as they do in Europe

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  11. That plant sounds like a terrific idea. Our local coppicers use the wood (mostly hazel and hornbeam from very ancient stools) for their stoves. There probably needs to be more awareness of the uses and beauty of coppiced wood. Minsmere Bird Reserve, for example, do a brisk trade in coppiced pea sticks.

    Re. sawdust pellets. I ran a test last winter on the different kinds, including hemp and rape. Most burned well but quickly in my Aarrow stove (similar to John's) and were great for start ups. The rape was the best.

    Any ideas on how local councils could use (and sell) wood rather than chipping it?

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  12. I break all the rules....

    Chimney unlined (someone said if it's rough concrete it's ok). I sweep every spring but the bulk of deposit falls as hard tar to the bottom trap box.

    Burn any old wood rubbish clearings etc from my 2 acres never as old and dry as should be and always rubbish wood like willow.

    Leave the door open to get max radiant heat (but not if room unoccupied). I like to scorch in this weather.

    (Anyone who reads the mag Nexus may remember the Scottish engineer who died last year who advertised (and campaigned) for his open stoves for maximising heat retrieval. Considered doors inefficient and dangerous! Perhaps he was right - who knows?

    By the way my son bought a cheapo Chinese stove which only lasted a couple of years...go for Scandinavian varieties.

    I'm reluctant to use chain saw and manage with 21 inch bow saw for logs up to 5in diam. The secret is to replace the blade frequently and it slices through easily.

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  13. very interesting to read as someone thinking of putting in a log burner

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