- Can I use wood fuel to provide heating and hot water?
- Where can I buy pellets?
- How many tonnes of pellets am I likely to need?
- Could I be self-sufficient in wood?
- How does the running cost of using a wood heating system compare to using a fossil fuel?
- What size boiler/stove do I need?
- What are the emissions from burning wood?
- Can I burn wood in a smokeless zone?
Wood fuel is one of the most appropriate renewable energy technologies for heating buildings. In a domestic property, the two fuels to consider are logs and pellets. Woodchips are not generally suitable in a domestic property because of the amount of space required for the equipment used for handling and storing them. Generally speaking, your heat demand would require a boiler with an installed capacity of at least 50kW before you would consider a woodchip boiler. If you have that, woodchips are a very cost-effective option.
Pellets can be purchased across the whole of the UK, bagged and loose.
Obviously, a lot will depend on how energy-efficient the building is and how often the heating is on and the thermostat settings. Each tonne of wood pellets will produce approximately 4,800kWh of heat (assuming they're burned in a 100% efficient appliance). A small, energy-efficient home might only need 2 tonnes of pellets per year. – a larger, less efficient home might need something like three to four tonnes per annum. If you're thinking of switching to pellet heating, your existing heating bill will provide a useful guide. Heating oil produces 10kWh of heat per litre (again assuming 100% appliance efficiency). If you don’t have any energy bills, the Energy Performance Certificate (EPC) for a domestic property can provide a useful guide as there is an estimate on the final page of the kWh that your home will needed for heating and hot water.
You would need to have sufficient land to produce 6 to 12 tonnes dry logs per annum. This could be done by planting a hectare of poplar which, after the third year, would produce approximately 10 tonnes of logs each year.
It's 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 of wood purchased and its delivery distance (particularly for solid fuels such as logs and coal).
In today's market woodchip, wood pellets and logs are generally a cheaper way of heating than electricity, heating oil or LPG. In some instances they are also cheaper than natural gas.
The Biomass Energy Centre tracks fuel prices on a quarterly basis. To find out more go to The Biomass Energy Centre website.
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's dependent on many factors including levels of insulation and draught proofing of the building, the lowest outside temperature for 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's important to bear in mind that all biomass boilers burn most cleanly and efficiently when working at their maximum output. Therefore, it's 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.
The main emissions from burning clean, seasoned wood 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. These emissions 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 need to consider seriously the appliance that the wood is burned in and the quality of the wood fuel that is used. Information on buying wood as a fuel is here.
To benefit from the domestic Renewable Heat Incentive wood fuel systems must not exceed the maximum permitted emissions limits of 30g per gigajoule (g/GJ) net thermal input of particulate matter (PM) and 150g/GJ for oxides of nitrogen (NOx). Systems installed between 15 July 2009 and the start of the scheme will not need to meet this requirement.
Wood can be burned in a smokeless zone if the appliance (stove or boiler) has an Exemption Certificate. Companies which manufacture log stoves with Exemption Certificates include Clearview, Vermont Castings, Dovre, Dunsley Yorkshire Stoves, Morso and Jotul.
There are also a number of pellet stoves and boilers that have Exemption Certificates. These include boilers and stoves manufactured by the likes of Binder, Extraflame, Fröling, Giles, Guntamatic, Hargassner, KWB and Solarfocus.