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Fuel cost, followed by appliance cost, are for most people the major factors in choosing a heating system. However, it is not always easy to make comparisons as different fuels have different calorific values and are sold in different units (tonne, litre, kWh).
The Heat Cost Calculator and Comparator (below) has been developed to provide an objective method of calculating the cost, in pence per kWh, of heat from a variety of fuels at their current price and, therefore, be able to compare the costs of heating with different fuels. Examples of situations when the Heat Cost Calculator & Comparator will be of benefit include:
- When considering switching from one fuel to another for example, changing to a renewable fuel such as wood chip or pellets;
- For a supplier of pellet, chip,willow and miscanthus, to determine a market price.
The costs of purchasing, installing or maintaining heating applicances have not been taken into consideration. For some renewable fuels this can be very high.
The comparator takes into consideration.
The calorific value fo the fuel. This is important and every effort has been made to obtain an objective figure (see note 1)
The efficiency of the heating appliance, in terms of delivered heat. Electricity is taken as 100% whereas for all the others 85% was used. Chip boilers may be lower, anthracite boilers and log stoves may sometimes be much lower but oil boilers nowadays can be up to 97%. Although gas is sold by the kilowatt hour, the appliance will not be 100% efficient hence the need for the separate column on the chart. If you know the efficiency of your appliance then multiply the fuel price by the percentage efficiency, divide by 85 then use this new price in the comparator. Conversely, having obtained a price for an alternative fuel multiply it by 85 then divide by the efficiency of the appliance.
The moisture content of wood, which can be highly variable 50% (by weight) has been used to represent freshly felled timber although this can be even higher in fresh local spruce whilst hardwoods tend to be lower. 35% represents partly air dried timber, 20% air dried timber. 10% moisture (as in wood pellets) would also be found in kiln dried timber. Prior drying is always advantageious. If your wood supply is at a different moisture content then use the following formula to find the cost in pence per kWhour, assuming applicance efficiency of 85%:
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Pence / kWh = |
Actual £ / tonne
45.42 - 0.52M
(where M is the % water by weight) |
OR |
£/tonne = |
Actual p / kWh x (45.42 - 0.52M)
(where M is the % water by weight) |
Factors not taken into consideration
Costs of purchasing, installing or maintaining heating appliances. For some renewable fuels this can be very high.
Although every effort has been made in preparing this chart, it should be taken as a guide only. Those wishing to make financial decisions involving fuel prices are advised to obtain independent confirmation.
| NOTE 1: For heating oil, the figure used is 12.83 kWh/kg oil (UK Parliament, Select Committee on Environmental Audit Fifth Report, Annex to Appendix 1). This translates to 10.27 kWh/litre, an average based on the density provided by oil suppliers. Supporting evidence is to be found in the Department of Trade and Industry website (www.dti.gov.uk)'Estimated average gross calorific values of fuels in 2002', The Carbon Trust (www.thecarbontrust.co.uk/foundation/0301prot.html) although it is unclear which is domestic heating oil. EnTech Energy Consultants Ltd (www.entech.co.uk/entech/ener_conv.htm) provide a slightly lower figure of 12.778 kWh per kg or 10.22kWh/litre.
For dry wood including pellets, the figure used is 5.36 kWh/kg. This was based on information from the DTI website, cited above, The Carbon Trust, op cit; British Biogen; internet site techTP.com/wood; Jannesch, R. 'Changing the energy climate: clean and green grass biofuel pellets', Resource Efficient Agricultural production - Canada, see www.reap.ca
For anthracite the figure is 9.42 kWh/kg from the DTI website op cit.
For LPG the figure is 7.4 kWh/litre from The Carbon Trust website, op cit.
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[The Heat Cost Calculator and Comparator was prepared by Andy Stewart, Coed Cymru 01686 650777].
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How to use the Comparator
- Locate the price you are paying for the fuel (in pence per litre of £ per tonne) on the appropriate fuel column
- Move horizontally to the dark blue column and read off the heat cost in pence per kWhour.
- Continue horizontally to find the equivalent cost of a different fuel. How does this price compare with the market price of that fuel? Should you consider changing?
Coed Cymru, The Old Sawmill,
Tregynon, Newtown,
Powys SY16 3PL
Tel 01686 650 777
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