Coppicing and woodstoves

Bruce Hocking

CRAGger Cornwall

Hi Robin

My coppicing has some guiding principles. Cut wood in the late autumn/winter. Season wood for 2 years. All trees have the same fuel value per kg at 18% moisture. Almost all parts of the tree are usable (tiny branches make good kindling). Wood must be burnt in a closed woodstove (efficiency 70% plus).

I started during the winter of 05/06, using hand tools on trees with up to 7” diameter trunks. Mostly alder, with the odd birch and hazel. The trees were both field planted and overgrown hedgerow. I tended to cut to cord length in the field and do my logging in the woodshed. For the winter of 06/07, I used a petrol chainsaw for my field work and an electric chainsaw for my woodshed logging. I have just bought an electric sawbench for the woodshed, which should be much faster than the electric chainsaw.

My aim is for a 5 year coppice rotation and first year regrowth from the Alder looks very promising.

Regards

Bruce

robinsmith3

website team CRAGger Islington Leeds Wokingham WSP

Hi Bruce

Thanks for this. Can I ask which woodstove you use and I assume you have a rural property with plenty of land around. I will point my friends at Thames Valley Energy to this link, they will be interested in your process as an agency specialising in short rotation coppice and other biomass energy technology.

I like your numbers for the car/train comparison too. I calculate my 1.6 petrol enginge car csots about 25p/mile too. However I have been monitoring my rail costs and find that for the journeys I make by train the costs are almost the same per mile. I dont know about carbon costs though, the end of the carbon year will tell. Trains are a funny one to guage on emissions, costs etc due to the huge subsidies rail gets. Its not that obvious

Best regards
Robin.

Bruce Hocking

CRAGger Cornwall

Hi Robin

Sorry for the delay. At the moment I have a Jotul No 1 (Norwegian and 20 years old). It’s a big egg-shaped stove with a solid door, which can be slid underneath if you want an inefficient (but romantic!) open fire. I’m very excited by the new generation of woodstoves which have self cleaning glass doors and secondary combustion and hope to have a Scan Anderson 4.1 installed in another fireplace for the coming winter. If the Scan is much more efficient than the old Jotul, then I will end up with 2 Scans!

As you assume, I do have a rural property with plenty of land, but the amount of wood that I have got from a relatively tiny area, is amazing. However, I have started with overgrown coppice, so have got a higher than normal initial yield.

Best Regards

Bruce

John Cossham

CRAGger York

I love my woodstoves and they form the backbone of my low-impact lifestyle. I have two smokefree ‘Clearview’ Stoves,(built in Shropshire) one is 8Kw the other is 4.5Kw, both are flat topped so they are used to heat water (kettle, big pan for washing up, 2 6 gal cans for bathwater) and cook on them, and dry fruit which I get as part of my compostables collections. The fruit needs to be some way away from the hot top, or it will burn, and most often sits on top of the bathwater pans which act as a heat store and stay hot for 24 hours after the stove goes out.

My fuel is waste logs from gardens, nearby parks and the University campus, all brought back in my cycle trailer. Occasionally a neighbour or passing donor pops one down for me, or a grateful tree-surgeon unloads the van. I use a big bowsaw for under 20cm dia logs, bigger ones I chop with an electric chainsaw. I split with a maul or splitting axe, and a log grenade wedge, but if the neighbours comment on the banging I get my electric hydraulic splitter out, but I try to do most of it by human power.

I stack in open air, not covered, they dry even in the rain, and have a pair of covered stacks either side of my front door, for final drying, with one in use, the other drying. I estimate I burn 6 tonnes of wood per year, but my electricity bill is low (£200 per year from Good Energy 100% renewable) and gas bill is under £50 this year, mainly my wife’s baking bread and cakes, and summer ‘instant’ hot water. We haven’t used the gas central heating for several years.

When I moved here I got both chimneys lined with insulated concrete using the ‘inflatable sausage’ method and LaFrage cement which uses old tyres as fuel.

I love my woodstoves very much.

John Cossham, York

John Cossham

CRAGger York

Materials from coppiced trees are obviously burnable on woodstoves, but as the diameter of the ‘logs’ would be generally quite small (thin) these sticks would burn quickly and the stove would need refilling often. Coppiced material would be fine for lighting a stove, or for using in stoves which use woodchips with an autofeed, once chipped. The majority of woodstoves work best with chunky logs with a diameter of perhaps 10cm, and these will burn for quite a long time and the stove will only need attending to every hour or half hour. Coppiced wood would work well for a type of stove design (unusual in the UK) which uses a fierce blaze which heats masonry and is lit only once per heating cycle, say once a day or once every 6 hours.

Coppiced sticks are excellent for making hurdles (a type of fencing)and other woven things and some other items including bean poles etc. Once they have been used for this, and the hurdle etc has started to decompose or break, it can of course be used for heating!

I approve of CRAGgers (or anybody else for that matter) reusing old coppice and bringing it back into operation, as they’re great for wildlife (biodiversity) and renewable raw materials, including fuel for stoves, combined heat and power stations, etc.

david

website team CRAGger Sevenoaks

I’d be interested to hear how Bruce finds his coppice wood fares in his woodstoves, since it seems it’s what he’s planning. I assume he’s happy to be continuously stoking, or is he waiting for thicker trunk widths before harvesting?

If coppice wood is unsuitable for long-burning directly in woodstoves, how about as a feedstock for pellets? If so, perhaps the cost of machinery would be prohibitive for small community groups. It’s worth investigating, though.

Thanks, John, for your help!

I have a small willow coppice which I have been experimenting with for 11 years. I have found that if you do not coppice for about 4 to 5 years you get reasonably sized logs. If you do this some of the smaller coppice stumps get crowded out and die, but I am pretty sure you get as much timber.

John Cossham

CRAGger York

I agree that coppiced willow left for several years does give you resonably sized logs (I have a pollarded willow I repollard every 4 or so years) but you’ll find that willow isn’t the best wood for burning…it’s very wet and needs a lot of drying, and it doesn’t burn particularly well, compared with beech, ash, holly, apple, oak, chestnut etc, but is better than poplar, which is really crap.

Use coppice for chips/pellets, Drax power station is! They’re adding a percentage of willow and other biomass to their coal. Use coppice for making things. But for good solid hardwood logs, and plentiful softwood timber, use tree surgeons (who’ll either give logs for free, or deliver for a small fee) and keep eyes and ears open for chainsawing ops, go and say hello, can I have some of your logs if you don’t want them (they nearly always say yes!)and of course, raid skips for offcuts of building timber.

Using a variety of sources for your renewable fuel makes sense. Different timber has different heat outputs, so when I need to fry something on my stove, and want it hot, I put on hawthorn, one of the hottest burning. In the summer, when less warmth is needed, and I just want a big pan of warm bathwater, I use willow or softwood offcuts, or leylandii.

Bruce Hocking

CRAGger Cornwall

All woods have the same fuel value/kg when dried to the same moisture content and all burn well in closed woodstoves.

I coppice lots of Alder, which is a very wet wood. However, I dry for 2 years (standard practice) in an airy shed and get very good results.

The stove mentioned earlier as needing to be fired once during a heat cycle is known here in the States as a masonry heater, and it interests me greatly in that in addition to needing less wood per heat cycle than a typical stove, it burns much more cleanly because of the way that it burns. My understanding is that because it burns very hot and very fast, it utilizes more of the wood, i.e., burns the gases produced from the wood as well as the solid, plus because it burns hot, the wood burns- it doesn’t smoke, which also reduces emissions. My intent with my next home is to install a masonry heater to replace whatever heating system that comes with it, and I am also interested in developing and maintaining a coppice because it is a sustainable practice. To that end, I have been researching trees that are suitable for coppicing and I think you folks should know about the black locust (Robinia pseudoacacia). Despite the fact that it is relatively short-lived tree (most information indicates 75-90 years) it has a rapid growth cycle, is drought tolerant, requires low fertility, is a valuable fuel wood, and has the capacity for fixing nitrogen in the soil. In addition to that, it’s widely grown all over the northern hemisphere and is useful for bee fodder (flowers) and animal fodder (leaves) and in the case of chickens can completely replace alfalfa as fodder. That said, it does sucker, so if you haven’t the room or inclination it could be a pest. However, I think an interesting tree to consider for coppicing. Thanks to all for interesting comments; I’ve learned a lot here and expect to check back often.

david

website team CRAGger Sevenoaks

Interesting. It’s known as pseudoacacia here, and is quite common in gardens – we have one in ours. But I never knew its history or potential as coppice – thanks!

http://en.wikipedia.org/wiki/Black_locust
http://www.the-tree.org.uk/BritishTrees/TreeGallery/falseacaciac.htm
http://www.bbc.co.uk/gardening/plants/plant_finder/plant_pages/733.shtml

Bruce Hocking

CRAGger Cornwall

I burn coppiced wood in my 20 year old stove (see above) with no problems at all. I especially enjoy burning thin poles and attend my stove approximately once per hour. I think you must have problem stoves if you can’t burn small diameter wood without it blazing away like mad – I definitely prefer Scandinavian stoves.

Coppiced wood comes in all diameters, mainly depending on the coppice cycle, but the advantage of short rotation coppicing has always been the small diameter of the trees which enabled them to be worked with hand tools.

My stove cost me £200 and it did not need a chimney liner!

John Cossham

CRAGger York

I’m not sure Bruce is correct in saying all wood has the same fuel value per kilo when dried to the same moisture content, but my info may be wrong too. What I ve been looking for since reading this comment is a sheet from a workshop I attended which was about this issue, which woods were more valuable as fuel. I cannot find the info but when I do, I’ll post it for all of you to read.

The jist of the info though was that different wood DOES have different calorific values per cord (a volume measurement) and because of this, you’ll get more heat per cord from certain species and less from others, as I indicated in a previous posting. The data sheet was very detailed, and fascinating reading, I will find it!

Bruce is correct that any dry wood will burn in enclosed stoves, but both mine are licenced to be used in smoke-free zones, because of a patented way in which the firebox air is delivered, preheated through a labyrinthine ‘turbo baffle’ which delivers the hot fresh air through tiny holes, creating jets and loads of turbulence. The chimney liner isn’t always essential, but it really helps to have a good ‘pull’ and a non-kinked, smooth-surfaced flue is always the desired situation. Consult your stove dealer!

What I do know from experience and reading is that stove owners/users definitely prefer certain species of tree as fuel, and some shun willow and poplar as they are widely redarded as being not worth processing and drying for so long. Many like ash as it will burn green (off the tree) as will holly. Burns better and smoke-free in my stove when dried for a year or two though..

Im sure Bruce and I have more in common than differences!

John Cossham

CRAGger York

I have found my data sheets and done some research.

Bruce is correct in saying that all species of tree produce wood with a similar calorific value per weight when air dried to 20% moisture content, although there IS a measurable difference between species.

However, different woods have very different densities, and very different burning characteristics, and therefore a cord (a stack of logs 4 feet by 4 feet by 8 feet, 128 cubic feet, wood vol approx 80 cubic feet) will give different ammounts of heat depending on the type of logs and how they’ve been cut and stacked.

For instance, a cord of air-dried willow weighs 2160 pounds, hickory 3830 to 4327 pounds. A better way of understanding the relative heat value of different wood is to look at the density, pounds per cubic foot: Hickory 50.9, Beech 44.2, Willow 27. Wet wood has only half the heating value of dry as much of the energy is taken up evaporating the water, and it produces smoke whereas dry wood in an enclosed high efficiency stove doesn’t.

For a start on the burning characteristics, this is a starter:

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 wood man’s cries

Beechwood 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’re old and dry
Larch logs of pinewood smell
But the sparks will fly

Pine is good and so is yew
For warmth on wintry days
But polar and 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 burn like wax
You should burn them green
Elm logs like smouldering flax
No flame is seen

Pear logs and apple logs
They will scent your room
Cherry logs across the dogs
Smell like flowers in bloom

But ash logs all smooth and grey
Burn them green or old
Burn up all that come your way
They’re worth their weight in gold

Anon

(of course, with a stove, there shouldn’t be any smoke smell in the room!)

John Cossham

You are both right.
Woods do have the same fuel value per dried kilo.
Some woods do have more fuel value per cord.

The old question of which is heavier, a pound of lead or a pound of feathers? comes to mind. The weigh the same but the feathers take up mich more space.

The energy value difference is because some woods are very dense and others are much lighter. Balsa wood is very light per volume. An equal sized piece of mahogany is much heavier. Some woods are so dense they don’t float, they sink.

Most of the time you buy wood by the cord, a volume measurement so you want an energy dense wood. That also affects the price you would pay as wood sellers also know of these differences in wood energy + quality.

You don’t usually buy wood by weight. You don’t know how long it has been seasoned and how dry it really is. The volume of a cord of wood doesn’t change that much during seasoning so is an easier measure of wood.

I don’t know how much the energy values of different woods are but some are easier to start, some are good at keeping coals overnight for starting again in the morning. There are many other differences and everyone has their own preferences.

Mary Paul

I was very interested to read that you are coppicing alder. I have access to an old coppiced alder wood (approx 2 acres)which hasn’t been coppiced for at least 40 years. The trees look old and not in the best of health with quite a lot of rotten branches. The owners of the woodland have been wondering whether to try coppicing again, but are afraid that it might kill the trees after so many years. Any advice?
Alex Loftus,
Redland,
Bristol.

david

website team CRAGger Sevenoaks

I don’t really know the answer to your question, Alex, but there’s some good general advice on “Reviving Derelict Coppice” in the BTCV Handbook on Coppicing, available online:

http://handbooks.btcv.org.uk/handbooks/content/section/3756

That might be useful! The rest of the book is a great resource, too.

Hi Alex,

1. Alder is not good as firewood – it inhales heat from the room.

2. Though used for many things Alder was often used to spile underwater as it lasts for many years when stored anaerobically. Indeed I believe that during some reconstruction of the A1 some 50 years ago engineers dug up a section of road laid may be as far back as 500 or so years – some fascines laid to corduroy a boggy section. Not bad, considering the traffic it had sustained for that time was away above anything contemplated.

Also to spile embankments to keep rivers from encroaching on leas or water-meadows during normal flows.

3. If you have really old coppicing stools, treat them with care. Crop them gently – the act of cropping will engender new root development but it can’t all be done in one fell swoop.

4. Remove rotten wood as quickly as you can but without taking too much “live-wood” – allow that to support the plant and then selectively cut it, maybe up to a quarter or even a third of the growth.

After a year or two you will have renewed the stool and it may live another 100 years. When growing strongly again, cut back any diseased wood (burn) and paint over any damaged areas with a good plastic paint.

As with any coppiced wood – the fewer re-growths you have the quicker and the thicker they grow. Selectively pruning the re-growth to the size you eventually wish for, unfortunately only experience can help with this – e.g. my great uncle had a coppice for firewood – he pruned the ash and oak back to three shoots per stool and cropped 150mm wood for heating and cooking (yes, that long ago!), about every seven years. The hazel he allowed to shoot more and used that for various things as well as kindling.

Hope this is of help.

John Cossham

CRAGger York

Hey, glad someone agrees about alder (and some other types of wood) not being very good for providing heat, when last year someone posted a comment saying that all wood had the same calorific value per kilo, which I don’t agree with. However I’m not sure what the author means by the alder fire ‘inhaling heat from the room’... perhaps this is more to do with using an inefficient open fire with an open flue (about 15% efficient) rather than a stove (sometimes up to 85% efficient) which doesn’t continually leak heat up the flue as the flue can be closed off or reduced in flow, keeping warm air in the room.

A stove stoked with dry alder will produce heat, but not much for the amount of sticks put on, and my favourites for good heat are hawthorn, beech, oak, apple, ash, holly and my least favourite (ie I say ‘no thanks’ to offers of these woods) are poplar and willow, and alder, if it was offered ever!

John Cossham, woodstove addict, York

Bruce Hocking

CRAGger Cornwall

Hi Alex

Just thought I should give you an update, as this winter I am burning Alder which has had the required 2 years drying and is at the optimum 18% moisture. The heat output is amazing and my woodstove is running from 8.00 am to 11.30 pm on 1 basket (standard fireside log basket) of Alder logs.

You and/or any other CRAGgers interested in Alder coppicing are welcome to visit me to see both the coppicing and the in-stove performance.

Best Wishes

Bruce

John Cossham

CRAGger York

Hi Bruce, I’m glad you are able to use your local supply of Alder and it’s working well. I’d love to come and see your coppice and working stove… what part of the country are you in?

And I have just seen a wicked stove called a ‘Dunsley Smokefree Boiler Woodstove’ which heats radiators AND is able to be used in a clean air zone. It’s amazing! And a resource for stove buyers is ‘firesonline.co.uk’ which has a range of stoves, although not the Clearview.

John Cossham

Bruce Hocking

CRAGger Cornwall

Hi John

I’m in Cornwall if you feel like a quick train journey!

Thanks for the info on the Dunsley Boiler – it might be just the thing for me as I have an oil-fired central heating system that I prefer not to use.

Did you see this stove in a shop or in someone’s house? If it was the latter, can you find out how much wood it uses and if the glass stays clean (always a worry with boilers)?

Bruce

John Cossham

CRAGger York

Oh Bruce, what a disappointment that you are so far away, I’m afraid I’ll have to give it a miss, seeing your stove and Alder Coppice would have been lovely but I’ll imagine it (unless you’re on Facebook and have an album of photos to share?)

As for the Dunsley, it’s in CRAGger Robin’s front room and the glass was reasonably clean. I’ll forward your posting to him and ask him to either let you know if it stays clean or let me know and I’ll tell you. It gives him radiators and bathwater, pretty groovy, I want one! And using firesonline.co.uk it wasn’t too expensive.

Hope you get one and can use more of that coppice!
yours, John Cossham