Firewood ~ by Jonathan
According to folklore firewood will heat you three times:
When you cut and extract it,
When you split and store it,
When you carry and burn it.
A wood fire can cook food, act as a focal point, or heat one room or an entire house.
In the wider picture, the careful and efficient use of firewood, a carbon neutral resource, can also contribute to reducing our dependence on fossil fuels and reduce global warming provided it is sourced, managed and transported sustainably.
Types of firewood
The type of firewood depends on use. A safely organised and atmospheric outdoor fire will require tinder, kindling and main fuel which can be derived from all parts and types of hard or soft wood trees. Naturally the dryer the better. Birch, cherry and cedar bark can be used as tinder, and for a slower, longer-lasting fire then harder denser sticks and logs are best once the fire is underway. Although less dense, softwood conifer sticks and twigs are good for kindling (including pine cones) as being more resinous they burn hotter and are easier to ignite. Pine and larch also give off a fresh outdoors fragrance but conifers are not recommmended for cooking with. To see some different types of outdoor log fires for either heating or cooking purposes click link here -
http://www.inquiry.net/outdoor/skills/b-p/wb/fires.htm
If you do not have an indoor fire but are thinking of getting one, then it is best to seek advice as to the most suitable type, capacity and installation for your room or building.You should also first check to see if you live outside a smoke control area. Click on uksmokecontrolareas.co.uk to find out.
Looking at the different firewood options for indoor fire places or woodburning systems in order of highest efficiency first:
A wood or biomass boiler burns mainly woodchips or pellets and is the most efficient (65%-95%) in terms of heat generation and waste, using all the converted main and by-products from felling. They are however more suited to serving a larger farmhouse, group of houses or commercial application.
The more common woodburning stove, with closed doors to control air and heatflow, and which ranges in efficiency from about 40-70%, will burn both hard and softwoods efficiently so long as they are sufficiently dried for at least a year and preferably two summer seasons. Given like for like moisture content (ideally down to 20-25%), there is little difference in the calorific value between hardwood and softwood, but there is a difference in weight density. Hence an oak log may contain double the energy as a similarly sized spruce log. Logs should be split no more than 10cm in diameter as this maintains a high area of reaction surface which is vital in generating enough heat during the early three endothermic stages of a fire (where temperatures reach up to 250°C) and allowing progression through to the clean and complete combustion stages (which occur at about 700°C). Freestanding stoves are more efficient than built-in stoves and the better stoves have both primary and secondary air systems which are crucial to the fire going through the full six phases of the burning process ensuring maximum heat output and clean efficiency. The enclosed stove also provides the visual glow and cheery sensation of a flickering flame if it has a good sized clear-view glass window.
For an open fire, which has the lowest efficiency of converting fuel to useful heat (10-35%) due to poor air control, generally seasoned hardwoods are best because they are less likely to spit or create smoke or tarry (and creosote) deposits in the chimney. However once seasoned properly, conifer woods which are easier to split and softer hardwoods such as birch and sycamore can be mixed with harder firewoods and still create a good, red, hot and virtually smokeless fire.
Supply and quantity of firewood
In medieval times, country folk were allowed to collect as much deadwood as they wanted from the royal forests – just so long as they could reach it “by hook or by crookâ€Â.
Presently there is an increasing demand for logs and woodburners – triggered largely by recent soaring energy prices as well as lifestyle/environmental choices – which has made finding good firewood more challenging and has caught suppliers on the hop. In certain areas suppliers are being forced to buy logs from further away and in future there could be a shortage of locally sourced, good-quality, seasoned hardwood logs unless better and less profligate forestry and woodland management techniques are adopted. Effective woodland management must also ensure that a whole array of flora and fauna is continuously supported and conserved which includes leaving plenty of dead wood lying around.
If you are lucky enough to have your own woodland then it can provide some or all of your firewood requirements depending on the woodland size, tree species present and the way the woodland is managed. The easiest way to do this is on a coppice cycle. If you have firewood that is surplus to requirements then you can always give or sell to a friend/neighbour or supply a local reseller.
If you need to supplement your own supply of wood then the good news is that wood supplied as domestic fuel attracts only 5% VAT (as do the appliances that are dedicated to burning it, provided they are installed by professionals). As a rough guide, to entirely heat a well-insulated 4 bedroomed house all year with an efficient woodburner stove or system requires 7 tonnes of air-dry wood a year (14 tonnes green wood). One acre of well-managed woodland will produce 1 tonne of dry wood per year so it would need about 7 acres to produce enough firewood on a sustainable basis. A greater area of older, more mature woodland is required since this is slower growing.
Main references or other useful info sources:
http://www.smallwoods.org.uk/pages/woodfuel.php
Centre of Alternative Technology booklet – “Home heating with woodâ€Â
http://www.guardian.co.uk/environment/20...od-burning
http://www.wildeye.co.uk/trees/firewood.html
http://www.aie.org.uk/aie_data/aie_firewood.html
http://www.woodheat.org/firewood/firewood.htm
http://www.usewoodfuel.co.uk
I note this bit as being informative from the smallwoods link
Many people are going back to open fires and stoves, so what is the secret of efficient and enjoyable wood burning?
Buy your logs as far in advance as possible- if possible buy in the spring for use not in the following winter but in the one after that. Firewood needs to be stacked outside to air dry for a minimum of one year, with a cover over the top, but allowing the air to move through it. Without a cover over the top in the autumn the wood will be rewetted and its moisture content will shoot up. If you are short of space buy from a merchant who guarantees summer drying. Bring logs inside a few weeks before use to become house-dry, then bring more in as these are burned.
Wood gives off carbon monoxide or coal gas when burnt slowly, and needs to be burnt at a sufficiently high temperature of up to 700oC to break the wood down with air into ash, carbon dioxide and steam. Wood also burns less efficiently the larger the piece is, and is actually a poor conductor of heat. Logs burns best when less than 10 cm thick.
Air dried wood burns at 70% efficiency in free standing stoves, 60% in built in stoves and only 35% efficiency in open fires. The large log on the open pub fire is actually burning very inefficiently, not giving out maximum heat, putting most of its energy up the chimney and producing a lot of polluting smoke.
With open fires, a coal grate should be covered with a metal base plate. Reduce the area of the lowest part of the fire with sloping fire bricks to deepen the ash bed but leaving more space for logs above. A fine mesh spark guard should be used for safety. Maintain a fast burn with a few thin logs at a time until there is enough ash and charcoal present for a slow burn. Adding new logs on a fire set to burn slowly will create smoke and tarry deposits in the chimney, and smoke equals pollution. Once an open fire has reached the correct burn temperature there should be very little smoke.
Burning logs in an enclosed stove is more efficient and can be just as cheery as an open fire if you choose one with a good sized glass door. The better stoves have both primary and secondary air systems. Primary air is cool air that enters the fire at the base, providing the oxygen for the burn. Secondary air is air that enters from the base but is passed around the fire in a chamber to warm it first before channelling it onto the top of the fire. This secondary air will ignite the gases being given off by the wood (producing a beautiful ball of yellow flame), burning these gases at 600 to 700 degrees C, producing carbon dioxide and steam. Some areas, mostly in cities, are 'smokeless zones', where the use of woodfuel is restricted. Some woodstoves are approved for use in these areas, however, so check with your local council.
If you have a bit of land why not grow your own firewood? To do this the easiest way is with a coppice cycle. To entirely heat a 4 bedroomed house all year needs 7 tonnes of air dry wood a year (14 tonnes green wood). One hectare will produce 21/2 tonnes dry wood per year so it would need 3 hectares to produce enough firewood on a sustainable basis.
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