There are logs, chips and pellets.

The more handling the wood fuel is subjected to the higher the cost. Logs are bulkier. Chip has been processed and is more easily handled and pellet flows more easily still. Pellets are made from compressed sawdust waste products and is appx. 8x25mm in size. Chip fuel if handled efficiently is the cheaper fuel per kW supplied (if comparing to oil and LPG).  Chip is made from forestry thinnings and the chip must be of good quality.

Costs:
If you spend £500 per year on oil, consider a log boiler, if more than £1,000 a wood chip system. Logs locally here (at time of writing) are £40 per tonne and oil at 39p per litre. Wood chips at £40-50 per tonne at 20-25% moisture content, give heating 1.6p per kW hour. Heating oil at 39p per litre gives 3.9p per kWh. Heating with LPG at 20p per kg gives 2.32p per kWh- LPG is currently 31.45p.

Pellet are easiest to handle but cost more - about £3.00 per 20kg bag or £150 per tonne (incl vat) giving 4.7 per kWh.

Moisture Content (MC):
If the MC is >30% chip will compost, If the MC is a low percentage this will result in  high blade wear, higher energy consumption and particle breakdown and prouduction of dust.  Rough guide for moisture contents, Log 20%, Chip 20%, Pellet 8-10%.

It is important to consider quality of chip (or log) and the moisture content. Too wet and it does not burn well, too dry and it burns too quickly - aim for around 20-25%.

     To calculate moisture content %
     = we weight of sample - dry weight of sample            x 100
     _____________________________________
               wet weight of sample

Chip Volume / Weight

Conversion of dry (20-25% moisture content) wood
_________________________________________
1 tonne = 2 cubic metres of solid wood = 4-5 loose
cubic metres of chip*

*bearing in mind that chip size will have an effect, contents can settle in transit and density of wood varies.

To convert BTU to Kw divide by 3,400. Therefore 50,000 BTU is equal to appx. 15kw.

Chip usage:
Chip usage can be estimated as follows: one tenth per cubic metre per week ie. 50kw boiler will use 5 cubic metres per week of chip. Pellets will be slightly less.

Chip store:
If you have the space and requirement for chip the store needs consideration. Chip store design is important, with 80% of the cost of wood heating during a typical life span of 25 years resting with the fuel - not installation. You must have chip of good quality (produced from a chipper designed for the job) and the chip must be clean (no grit, soil, old nails etc.). Consider how you will handle it from store to boiler. More information online here:-  http://www.swwf.info/woodfuel.htm

Boilers:
Rough guide for heat loads, domestic house 10-30kW, Farm house 30-50kW, mansion 75-150kW.

To produce a comfortable room temperature of around 70 degrees Fahrenheit, (21 degree / 22 degree celsius) when the outside temperature is zero, you will need about 1kW of heat for every 14 cubic metres of space. This is equal to about 1 bar of an average electric fire or 100 watts per m2.

Boilers need a certain amount of maintenance, clean every 2 weeks, this depends on fuel quality, contamination with soil will give clinker, reduce performance and create greater long term maintenance. High percentage of bark, needles and leaves in the chip fuel increases minerals and hence ash, leading to more frequent cleaning. Cost per kW installed approx £150-£250, varies on make, specification and size. For larger boilers the costs can come down to approx £100 per kW installed - ask your supplier for quote. Installation is more expensive than conventional boilers however a package of grants and a payback period of 5-10 years on fuel savings can start to look attractive.

Typical wood heating equipment from Germany/Austria £300-£400 per kW installed. Grants for private installation are rarely greater than 20%.
Hamech chip boiler from Poland 100kW system installed for £6-9,000
Vigas log boiler from Slovakia 25kW system installed for £3,000

Where does all the heat go?
Renewable energy and energy saving go hand in hand. Typical areas of heat loss in an average house:-

Buyers Guide
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Boiler Sizing Worksheet

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Wood Fuel Supply Contract
Suggestions when making arrangements to draw up a contract for fuel supply with your fuel supplier.
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