Biomass is rapidly gaining in significance as a source of renewable energy in the UK. People are increasingly heating their homes with wood-fuelled stoves or boilers, and the sophistication and versatility of such systems is constantly improving.
Wood is probably the oldest biofuel in the world, but the traditional sack of logs has been joined by other products, notably wood chips and pellets. Modern stoves can be over 90% efficient, and have thermostatic control systems and automated fuel supply. The technology has been developed in other European countries where wood is used much more widely. In Austria, for example, 80% of boilers installed burn wood pellets or chips.
Although the boilers are expensive, wood can be cheaper than conventional fuels, such as gas or oil, although this is not always the case, especially with pellets. Also, wood is essentially carbon neutral - the carbon dioxide emitted during combustion equals the amount absorbed during growth of the tree. However, inputs of energy for processing and transport must be considered, and a local supply of wood fuel is desirable to keep transport costs down.
Cutaway of automated feed for pellet-fuelled boiler
Types of biomass heating systems
Various systems use wood in different forms, but the two most popular are:
- Stand-alone stoves for space heating - can use logs, wood pellets, or a variety of solid fuels ('multifuel' stoves); output is typically 5-20 kW and the most efficient models are rated at around 90%. Some can be fitted with a back boiler for water heating
- Boilers for central heating and hot water - can use wood pellets, logs or wood chips, although automated feed systems for domestic boilers generally require pellets. Output depends on the size of heating system. A typical three-bedroomed semi-detached house will need a 20-kW rated boiler.
What will it cost?
Stand-alone stoves typically cost £2000-4000 installed, but the price of fuel is highly variable; some can burn logs that are obtained for free, whereas pellet-fired stoves can be expensive to run. Also, according to the Energy Saving Trust, space heating using a stove is relatively inefficient compared with a central heating system. However, such stoves do cut the household's carbon emissions.
Wood-fired boilers vary enormously in cost, depending on the type of wood fuel and the delivery system, but lie in the range £5000-£14,000 installed. Again, running costs may depend on the price of pellets relative to gas or electricity. Systems using wood chips are cheaper to run, but tend to be more expensive to install. Given a cheap supply of fuel, biomass boilers can deliver annual savings of over £400 on heating bills, compared with electric heating, and also substantially cut carbon emissions.
Pellet-burning stove for space heating
Grants
Grants for biomass-fuelled domestic stoves and boilers are available under the Low Carbon Buildings Programme, run by the Department for Business and Regulatory Reform (BERR).
For room heaters/stoves using an automated wood pellet feed system, the maximum grant is the lower of £600 or 20% of eligible costs.
Wood-fuelled boilers are eligible for a grant of £1500 or 30% of the cost, whichever is the lower.
Other factors to consider
- Safety and building regulations - check with your installer about compliance
- Flue design -make sure the flue vent is of a suitable type and its location allows effective venting of flue gases
- Fuel storage - space must be allocated for storing fuel and adequate access for deliveries
- Smokeless zones - check that your appliance is exempted under the Clean Air Act, as a 'clean burn' model