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Frequently Asked Questions
1. Why should I burn wood?When plants grow they use carbon dioxide from the air to make their wood. If you burn the wood the carbon is released back to the atmosphere. As long as you grow another plant/tree then a stable carbon cycle is set up. So ,the use of sustainably produced wood as a fuel does not increase the carbon dioxide levels in the atmosphere. 2. Can I use wood fuel to heat my home?Wood fuel is one of the most appropriate renewable energy technologies for heating the home. In a domestic property the two fuels to consider are logs or pellets. Woodchips are not generally suitable for use in a domestic property because of the ancillary equipment needed. 3. Can I burn wood in a smokeless zone?Wood can be burned in a smokeless zone if the appliance (i.e. the stove or boiler) has an Exemption Certificate. Companies which manufacture stoves with Exemption Certificates include Clearview, Vermont Castings, Dovre, Dunsley Yorkshire Stoves, Morso and Jotul. A full list can be found at http://www.uksmokecontrolareas.co.uk/appliances.php?country=e. Obtaining an Exemption Certificate is an expensive and lengthy process. There are currently no pellet burning stoves or boilers that are on the exempt appliance list, although many are tested to a high standard in their country of origin. 4. Where can I buy pellets?Supplies of pellets can be found on the Log Pile website http://www.nef.org.uk/logpile/fuelsuppliers/pelletsuppliers.asp and at http://www.bigbarn.co.uk/logpile/indexen.php (where a search can be done with reference to a place or postcode). Alternatively, NEF can send you a list of suppliers by the post. 5. How many tonnes of pellets would I need to heat my 3 to 4 bed roomed detached house?You would need about 5 to 10 tonnes of pellets to provide space and water heating if the house is not particularly energy efficient. 6. Could I be self sufficient in wood?You would need to have sufficient land to produce 6 to 12 tonnes dry logs p.a. This could be done by planting a hectare of poplar which after the third year would produce approximately 10 tonnes of logs pa. 7. How much does a wood fuel boiler/stove cost?A Log/pellet boiler for a domestic property will cost in the region of £3000. A large farmhouse might pay between £4000 and £8,500, with large businesses and community heating schemes costing significantly more. A pellet stove (without a back boiler) in the region of £1500. A coal or wood stove (or inset) with a back boiler to run 10 radiators would cost in the region of £600 to £700. In addition there is the cost of the flue and installation—typically in the range of £1000 to £1500 plus VAT depending on the type of heating system installed. In addition there will be the cost of fuel storage to consider. 8. How does the running cost of using a wood heating system compare to using a fossil fuel?It is always difficult to make comparisons between the cost of heating with different fuels, given that there are a number of different suppliers in the market, different electricity tariffs for day and night time and different costs according to the quantity purchased and distance (particularly for solid fuels such as logs and coal). In today's market, wood pellets, woodchip and logs are generally a cheaper way to heat than electricity and LPG and in many instances, oil. Mains gas is the cheapest way to heat where it is available. Further details are available at http://www.nef.org.uk/logpile/pellets/cost.htm 9. What size of boiler/stove do I need for my home?Heating output is specified in kilowatts, kW, (metric units) or BTUs (Imperial units) and represents the rate at which the system can deliver heat energy. Sizing of heating systems should be done by a qualified heating engineer. It is dependent on many factors including levels of insulation and draught proofing of your home, lowest outside temperature of your locality and patterns of use. However the following 'rule of thumb' can be useful for making initial sizing estimates for central heating boilers: Boiler size (in kW) = volume to be heated (in cubic metres) divided by 34 (for a reasonably well insulated house). It is important to bear in mind that all biomass boilers burn most cleanly and efficiently when working at their maximum output. Therefore it is best not to over-specify but to choose a biomass boiler which is sized to meet your average heating requirements with additional heating sources to provide extra heat on the coldest days. 10. How can I find out more about pellet production? Is it something worthwhile doing?Pellet production is carried out on many scales, from the purpose built large scale wood pellet production facility to small scale pellet machines or converted animal feed or grass mills. Further information on this is not something that is within NEF's remit. However, NEF did host a conference on this subject in February 2005 and copies of the presentations made by the various speakers can be found at http://www.nef.org.uk/logpile/conferences/pelletproduction.htm. NEF suggest that anyone with an interest in pellet fuel production contact one or more of the relevant speakers. 11. Can I used wood chips to produce pellets?Yes, you can but it is not an economically viable thing to do at present given the availability of sawdust (and imported pellets) and the additional processing required. 12. Where can I buy pellet producing equipment?Small scale pellet producing equipment can be purchased from Wood Energy Ltd of Pinkworthy Barn, Oakford, Tiverton, Devon EX16 9EU. Tel 01398351349. E-mail: info@woodenergyltd.co.uk. Web: www.woodenergyltd.co.uk. Also, from Cornwell Heat Ltd of Bells Lane, Hawstead, Bury St Edmunds, Suffolk, IP29 5NW. Tel 01284 386447. E-mail cornwellheatltd@btopenworld.com. Larger scale pelletising machines can be purchased from Amandus Kahl of Germany (http://www.environmental-expert.com/technology/amandus/amandus.htm) and Sprout-Matador through its sister company , UMT Ltd of Stockholm Road Sutton Fields, Hull, HU7 0XL. Tel 01482 825119. E-mail: sales.equipment.hull@umt-group.com. Web: www.umt-group.com 13. Are there grants available to help cover the cost of installing wood fuel heating?For domestic installations there are grants through the Low Carbon Buildings Programme, funded by BERR. It offers £600 (up to a maximum of 20%) off the cost of an automated pellet stove and £1,500 off the cost of an automatic wood fuel boiler systems, regardless of size, with a ceiling of 30% of the cost. In order to be eligible for the scheme, homes must already have high levels of insulation and use low energy lighting where possible. There is a related funding stream for housing stock managers. In order to be eligible for the Low Carbon Buildings Programme grant the chosen equipment must be on their approved list, proving that it meets European standards for efficiency and safety (EN303-5). In addition, the installation must be done by, or under subcontract for, an approved installer under the scheme. In Scotland, a similar scheme is run by the Energy Saving Trust under the name Scottish Community and Householder Renewables Initiative (SCHRI). In Wales, the Wood Energy Business Scheme came to an end in March 2008, but it is hoped that a new scheme will replace it during 2009. For commercial users, tax relief is available in the form of Enhanced Capital Allowances. Five categories of biomass boilers and roomheaters are covered by the ECA scheme:
14. What are the emissions from burning wood?The main emissions from a wood fired plant burning clean wood from forests or coppice will consist largely of water vapour and carbon dioxide (plus nitrogen and oxygen from the combustion air). The emissions will also contain traces of carbon monoxide, particulates and volatile organic compounds. However, these emissions are not exclusively produced by burning wood. They are also produced when fossil fuels like gas and oil are burned to produce energy. However, this is not a reason to be complacent. Instead it highlights the needs to consider seriously the appliance that the wood is burned in and the quality of the wood fuel that is used 15. Where can I see a wood fuel boiler system in action?If you would like to see a wood fuelled boiler in action we suggest that you contact one of the boiler suppliers and ask them if you might be able to visit one of their customer’s premises in your area. 16. What is the wood fuel requirement for a typical house?
You could substitute other biomass for wood (all biomass is around 18 GJ/tonne dry matter) and change the yield per hectare if you are thinking of Miscanthus. So as a rule of thumb, 5 tonnes of dry biomass to heat a typical house. 17. What are the CO2 emissions emitted per kWh by different fuels?The official Defra data for kg CO2 per kWh for different fuels is: Average grid electricity: 0.537 The figure for electricity has fallen - it was 0.80 in 1990. Please note thatthese figures are updated each year by Defra. Source: Defra’s greenhouse gas (GHG) conversion factors for company reporting For energy related emissions, the protocol is based on the product of energy consumption and CO2 emission factors. This approach can be used for determination of the project baseline and the forecast of annual emissions. The calculation of CO2 emissions is simply: CO2 emissions (tonnes) = Energy consumption (kWh) x Fuel emission factor (kgCO2/kWh) x 0.001 The emission factors for a range of different fuels are given in Table 1. In the case of electricity consumption it is in most cases impossible to identify with any certainty the source of generation that has been reduced or displaced. For this reason Defra publish an average carbon intensity factor for the estimation of carbon dioxide emissions from the consumption of electricity, taking into account all UK sources (including nuclear and renewables). However, for some purposes they recomemnd using a marginal factor, based on the extra capacity brought onstream at peak periods (mainly CCGT); this has been fixed at 0.43 kgCO2/kWh. Fuel can be purchased in a variety of units. Conversion factors for the most commonly used units are given in Table 2. Where fuels are purchased or measured by volume or weight the calorific value of the fuel is needed to convert to energy units. The fuel supplier should specify this, but where this data is not available default factors should be used. Default calorific values for selected fuels are given in Table 3, based on information from the Carbon Trust. The UK is moving from a gross calorific value to a net calorific basis; details on the implications of this change can be seen on the Defra pages referred to above. 18. Table 1. Carbon dioxide emission factors for energy related emissions
19. Table 2. Standard conversion factors for energy units
20. Table 3. Default calorific values
21. Relationship between kWh, MJ and cal 1kWh = 3.6 MJ |
Log Pile is a project from the National Energy Foundation which was supported by DEFRA.
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