• Producing logs
• Burning logs
• Log burning appliances
• Buying logs

Producing logs

Logs are usually produced from small round wood, which is delimbed, often in the forest, and cut into logs of typically 2-3 m in length. These may be stacked at ‘rideside’ for subsequent collection following a period of drying. On average 1 m3 of roundwood requires 1 linear metre of space.

To make a good fuel wood needs to be dried or seasoned to reduce it’s moisture content, which in freshly felled wood constitutes between 35% and 60% of the weight. Trying to burn wet wood will produce steam, less heat (as so much of it is being used to dry the wood) problems with the chimney (see below) and pollution.

Wood felled during one winter should be seasoned until the next before it is burned. Trees felled during the Spring/Summer will have a very high moisture content compared to those felled in late Autumn/Winter, therefore whilst a log first cut in January may be ready to burn within say, a year, it is necessary for a log cut in May to be seasoned for at least two years. Scoring or partial removal of bark helps to accelerate drying, as does splitting logs over 15 cm in diameter.

Whilst seasoning logs should be stored under cover in an airy place such as an open sided lean-to. If well stacked, a pile of round and split logs can show a bulk density 70% of that of the solid wood, though if loose this can drop to only 40% or less.

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Burning logs

Wood should be burned when the moisture content is below 25% - 'air-dry' - the bark will come away easily in the hand and the log will have splits across the grain. Logs to be burned in an open fire or log burner should be around 15-50 cm long (25-30 cm is the optimum) and split if greater than 10 cm diameter.

In terms of what type of wood to burn it is worth bearing in mind the heavier and therefore denser the wood, the higher its calorific value and therefore the longer it will burn. Hardwoods tend to be denser than softwoods such as pine and spruce and some of the densest are oak and beech.

However, some of the very dense hardwoods like oak and elm can be difficult to burn, so it is usually best to burn them with another type of wood as well. Softwoods tend to be easy to light and to burn quickly (making them good kindling). Some species like spruce and horse chestnut spit badly making them a hazard in an open fire. Some of the best types of wood for burning are ash, beech, hornbeam, hawthorn, crab apple and wild cherry.

Like other fuels, wood needs plenty of air to burn well. It is best to allow a fresh change of logs to burn freely until they almost turn to charcoal and only then to 'damp' down the fire by reducing the air supply. Filling a stove with logs and damping it down straight away, stops the 'volatiles' from burning and generates a lot of smoke and tar that is bad for health and the environment.

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Log burning appliances

To produce heat for one or more rooms logs can be burned on an open fire. These look nice, but tend to have low efficiencies - about 80-85% of the heat goes up the chimney.

A more efficient alternative is a wood burning stove; modern stoves have efficiencies in excess of 70%. With the right stoves wood can be burned in a smokeless zone. Some stoves can also be fitted with back boilers to heat one or more radiators or domestic hot water.

Logs can also be burned in a ceramic stove. These have extensive internal flues and can retain heat for up to 24 hours after the last firing. They can be around 90% efficient and some can be used in smokeless zones. Another option is a range. Ranges can be used for cooking, hot water and central heating.

There are also many domestic scale log central heating boilers available. Using wood to run the central heating system is often a cheaper option although the initial cost of the boiler will be more than a conventional one.

For a list of local suppliers of wood burning stoves and appliances our Wood Fuel Directory

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Buying logs

Although the price of logs has increased considerably in the last few years it is still one of the least expensive forms of heating available, especially when burnt in a modern, efficient wood fuel burner.

At the time of writing (January 2009) the average UK cost of a stacked cubic metre of seasoned hardwood was £70-80. The energy density of well seasoned hardwood is 4 kWh per kg, which equates to an energy cost of approximately 4.5-5 pence per kWh. This compares favourably with the present cost of bulk deliveries of other fuel types but using logs is a much more manual process. To see how this compares with other fuels see fuel costs.

There are many suppliers of logs in Surrey. See our Wood Fuel Directory for local suppliers, and the Woodlots directory for South East based suppliers. It is also worth looking in the Yellow Pages under 'Firewood' or 'Treework' (tree surgeons). Alternatively, you can look in the local papers for small ads for loads of logs.

Suppliers of wood should be questioned to ascertain:

• That the wood is from a sustainable source
• It has been seasoned and for how long
• The type of wood being sold
• Whether the price quoted includes delivery
• The length and general size
• Quantity by volume or by weight

Some suppliers can specify what species of wood they are selling although often, especially in the case of wood sold by tree surgeons, it will be a mixed load containing soft and hardwoods.

Although competitive for small scale users with stoves and wood fired cookers, buying in loads of wood is still relatively expensive for a large (boiler) user. It is much cheaper to buy unprocessed wood in bulk, at typically a quarter of the above cost, giving an energy cost of approximately 1 pence per kWh.

This requires work to cut, split and stack the wood and time and space for seasoning but despite the extra effort required this is likely to be the cheapest way to heat a rural home in the UK. It also enables the user to ensure the proper seasoning of their wood. Farmers and landowners who manage larger areas of woodland have even greater potential to reduce energy costs making wood-firing a highly attractive option.