Firewood - seasoning, storage, kindling, environmental issues

Firewood

Which is the best firewood for burning in the home? A guide to seasoning and storage of firewood and how to build and light the perfect fire.

By Piers Warren, author of British Native Trees - Their Past and Present Uses

Wood is the natural sustainable choice of fuel for domestic fires – in use since the first fire many millennia ago. When we warm our homes with wood, we participate in a natural cycle and an ongoing continuum of activity that we share with ancient ancestors. I am amazed at the number of country people who don’t have fires, whether open log fires or woodburning stoves, because they are “too dirty” or “too much work”. In fact the procedure of building and lighting the fire is one of my favourite jobs of the day, and I love handling and preparing the firewood. I am not one to pursue a life where all comfort comes from the flick of a switch.

Wood fuelled the open fires of the hunter-gatherers, the brick ovens of the first bakers, and, until the 19th century, all homes. We love to sit in front of a fire and watch its magical flames speak to us and warm our souls. Have you noticed that when the TV is switched off everyone stares at the fire? And watching a fire is certainly far more relaxing than watching TV! Fires inspire intimate conversation. When we come in from the cold, we are drawn to the fire. No other fuel is as alive.

The ability to burn wood for heat in your home gives you more freedom and options for fuel. You are no longer dependent on large energy utilities and multinational corporations who may or may not be able to supply power and fuel. Even if you have to buy in your logs at least you are supporting your local economy. But what are the environmental implications of burning wood?

Environmental Issues

When we burn wood we are releasing solar energy, in the form of heat, that has been stored in the wood as chemical energy. The process of photosynthesis converted solar energy, water and carbon dioxide into oxygen and the organic molecules that form the wood, half the weight of which is carbon. So burning wood is just the quick reversal of this process, liberating the sun’s heat when we need it most.

Unlike the burning of fossil fuels like coal, gas or oil, burning firewood releases no more greenhouse gases (carbon dioxide) than would be produced were the wood to simply rot on the forest floor. If we are responsible in the ways we grow, cut, and burn our firewood, wood burning can actually be a good choice for the environment.

Note that I mention ‘grow’ our firewood – for of course this must be done sustainably. There are many parts of the world where forests are disappearing as growing populations collect daily firewood without planting new trees. This is avoidable – wood is a renewable resource, which means that it can be replenished by nature in a period of time that is compatible with our human use. Provided they are cared for and managed properly, our forests can be a perpetual source of fuel, unlike gas, oil, and coal, which we are being depleted at a rate far faster than the millions of years it took nature to make them. On the smallholding it is up to us always to plant more trees than we cut down, and if we buy logs from a wood merchant, to make sure they come from a sustainable source.

Firewood So burning wood is a good choice from the greenhouse gas point of view but what about other pollution – surely all that smoke can’t be good? Smouldering, smoky fires that produce a plume of blue-grey smoke from the chimney are the main cause of wood heat-related air pollution. Smoke is made up of many tiny airborne particles and wood smoke can be harmful when it is inhaled. In some countries wood smoke has become a major air pollution problem and this has led to both local regulations and more efficient wood-burning appliances.

One thing to make clear at this stage is that if you are burning the right wood in the right way then there shouldn’t be much smoke. As you probably know from bonfires, a slow, wet fire produces lots of thick smoke – in the fireplace we are aiming for a quick, hot, dry burn producing very little smoke. Another thing to bear in mind is that a smoky fire is an inefficient one – we want all the released energy to heat our home – not to go up the chimney in the form of complex particles. Carbon dioxide, the product of a clean, hot burn, is a colourless non-particulate gas, so a hot fire with minimal smoke is an efficient energy-converter with less pollution.

Sources of wood

There are two main choices – buy it in or grow your own. If buying from a log merchant (such as Certainly Wood www.certainlywood.co.uk) you should expect to pay in the region of £100 for good truck load, although kiln-dried firewood can be far more expensive. Ensure the logs are well seasoned and dry – I have in the past received logs described as ‘seasoned’ (in that they were chopped a year ago) but soaking wet from lying about in the rain for weeks!

When I say ‘grow your own’ I realise not everyone is lucky enough to have a small wood! I don’t have a wood but I do have a lot of trees and hedges – and the prunings of these provide a large part of my fuel each year. Remember when it comes to pruning or felling you are often thinking a year ahead or more in terms of actually burning the wood, as it will need time to season.

Where I live, with no shortage of quiet country lanes, I often find large limbs blown off trees and lying in, or next to, the road. By taking these home for firewood I am doing the land-owners and road-users a favour – but do remember that this wood does belong to the landowner – so ask permission before helping yourself to logs on your Sunday afternoon walk through the neighbouring farmer’s wood.

As I own a chainsaw and associated kit (helmet, visor, ear protection, gloves, protective trousers and lumberjack boots) I often get free firewood by helping neighbours. So ask those living around you if they have any dead trees, stumps, damaged branches etc that they want removed – in exchange for the wood. At this point I must say that using a chainsaw is a dangerous and skilled job – so make sure that you have appropriate training. Many agricultural colleges do short courses in chainsaw use which are well worthwhile. Any work with a chainsaw above ground (ie using a ladder or climbing with ropes in trees) should be undertaken only by a qualified tree surgeon, or if you have had the necessary training.

Which wood?

So what sort of wood burns best? Well there is an old anonymous poem which answers this very question:

LOGS TO BURN

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 woodman's cries.
Never heed his usual tale,
That he has good logs for sale,
But read these lines and really learn,
the proper kind of logs to burn.

OAK logs will warm you well,
If they're old and dry.
LARCH logs of pine wood smell,
But the sparks will fly.
BEECH logs for Christmas time,
YEW logs heat well.
SCOTCH logs it is a crime,
For anyone to sell.

BIRCH logs will burn too fast,
CHESTNUT scarce at all
HAWTHORN logs are good to last,
If you cut them in the fall
HOLLY logs will burn like wax
You should burn them green
ELM logs like smouldering flax
No flame to be 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;
Buy up all that come your way,
They're worth their weight in gold.

Note that all woods burn better when seasoned and some burn better when split rather than as whole logs. In general the better woods for burning that you are most likely to come by (including non-native species) are:

Apple and pear – burning slowly and steadily with little flame but good heat. The scent is also pleasing.

Ash – the best burning wood providing plenty of heat (will also burn green but you should not need to do this!)

Beech and hornbeam – good when well seasoned

Birch – good heat and a bright flame – burns quickly.

Blackthorn and hawthorn – very good – burn slowly but with good heat

Cherry – also burns slowly with good heat and a pleasant scent.

Cypress – burns well but fast when seasoned, and may spit

Hazel – good, but hazel has so many other uses hopefully you won’t have to burn it!

Holly – good when well seasoned

Horse Chestnut – good flame and heating power but spits a lot.

Larch – fairly good for heat but crackles and spits

Maple – good.

Oak – very old dry seasoned oak is excellent, burning slowly with a good heat

Pine – burns well with a bright flame but crackles and spits

Poplar – avoid all poplar wood – it burns very slowly with little heat – which is why poplar is used to make matchsticks.

Willow – very good – in fact there is growing interest in biomass production of coppiced willow as a fuel.

Seasoning

So what is seasoning? Essentially it is making wood fit for burning – by reducing its water content – usually by leaving it for a period of time in the right conditions. All wood contains water. Freshly-cut wood can be up to 45% water, while well-seasoned firewood generally has a 20–25% moisture content. Well seasoned firewood is easier to light, produces more heat, and burns cleaner.

If you try to burn green wood, the heat produced by combustion must dry the wood before it will burn, using up a large percentage of the available energy in the process. This results in less heat delivered to your home, and gallons of acidic water in the form of creosote deposited in your chimney. This can eat through the chimney lining and cause significant damage. The problem is that as wet wood burns slowly, with little heat, the chimney flue does not get a chance to warm up. There is little draw (air moving up the chimney) which doesn’t help the combustion, and the flue remains a cold surface on which the creosote condenses. Dry wood will burn hot – heating up the flue, creating a fast draw, and shooting the smaller amount of vapours out of the chimney before they get a chance to condense.

The first step to drive the water out of the wood is to cut it into lengths – let’s say about 12–18 inches long (or less if your fireplace/woodburning stove requires this). Tree branches and trunks contain thousands of microscopic tubes which carry water from the roots to the leaves, and these tubes can stay full of water for years after the tree has been felled (or pruned). Cutting the wood to shorter lengths opens these tubes to the atmosphere which increases evaporation.

The second step is splitting any logs that are more than say six inches in diameter. This increases the surface area of the wood exposed to the elements and therefore also enhances drying. So the cutting and splitting of logs should be done as soon as possible after the wood is harvested – not just before you want to burn it. You can get mechanical splitters, and attachments for a tractor, when you have large quantities to split, but they are not cheap.

For the average user a maul is the tool needed. A maul is a type of axe with a heavy, wide head especially for splitting logs – you can buy one from a forestry supplier for about £40 new. A maul does not need to be particularly sharp – unlike a narrow felling axe which slices at wood and needs to be sharpened regularly. You can use a felling axe for splitting logs but it is much harder work than a maul. The trick with a maul is to let the weight of the head do the work – swing the maul over your shoulder and let the head fall on to the log without forcing it down. The wide head will force the log apart. It’s also important to have the log you are splitting at a good height – on a tree stump or larger log about 18 inches to 2 feet off the ground is ideal – this makes the job easier and avoids back damage.

It takes a bit of practice to start with, but once you’ve ‘got your eye in’ you should be impressively splitting each log first time every hit – and be able to keep this up for a few hours at a time without feeling exhausted. It’s a task I thoroughly enjoy – and have always referred to it as ‘earning my cow pie’!

The rest of this chapter which covers Storing Firewood, Kindling, and the all important Building of the fire are covered in the book: British Native Trees - Their Past and Present Uses
Click here for further information about the book and to order your copy

Reviews

"This is a reassuringly accessible, but authoritative, hands-on and up-to-date trot through information we need to know about our 21 genera of native trees. The author's style is a model of simplicity - free of jargon. The timing could not be better for a book which contains a whole section on wood burning, including environmental issues."
Forestry & Timber Association

"What a pleasing book. I was given mine as a present and I shall be buying many more for the same purpose. The author knows his subject but he also knows where to stop, which is a rare skill. You learn plenty within these pages, and some of it is quirky and surprising: but it's not a lecture! It's a human, friendly, practical sort of book, and the stuff about how to set and light a fire is worth the price alone. There's also a good 'resources' section at the end with lots of websites and addresses of interest to smallholding / conservation / tree-loving types. Excellent value for money. "