Technically, an open fire burning logs may be regarded as biomass heating, however this entry deals with more advanced, and much more efficient forms. Generally, large financial and carbon dioxide savings can be made compared with using fossil fuels, particularly if you burn logs and have your own source of wood.
Stoves - cost £1,000 to £5,000
fuel: 3-5p/kWh; CO2: 0.02kg CO2e/kWh
The most basic form of biomass heating in this context is the wood-fuelled stove. Generally intended as a single room heater, modern wood-fuelled stoves are an attractive centrepiece of any living room, as well as providing efficient, immediate, low-impact heating.
If the wood has been grown locally in well managed forests they may practically be considered carbon neutral, and the psychological benefits of staring into a naked flame are well documented. However, they are only able to radiate heat from their bodies, and so cold corners are likely to stay that way – they also require constant feeding and maintenance, which doesn’t necessarily fit with many people’s modern lifestyles or expectations.
Wood-fuelled stoves are available with back-boilers to provide hot water for washing or supplying radiators – the most sophisticated forms of which burn wood pellets rather than logs, providing greater convenience and less maintenance.
A wood-fuelled stove with back boiler can simply feed radiators immediately. However, if linked to a thermal store (hot water tank), it is also possible to link it up with a conventional boiler or another renewable energy heat source such as solar thermal. A stove with back boiler and solar thermal is a particularly good combination, as the stove can provide the majority of the heat demand in winter and the solar can provide most of the hot water required in summer.
A large number of different makes and models of wood-burning stoves are available, with or without back boilers. Back boilers can be bought separately and retrofitted to an existing stove, although the overall efficiency is unlikely to be as good as factory matched stoves and boilers.
There are a number of factors to consider before opting for a wood-burning stover:
- Firstly, whichever type of stove you favour, you must have an existing chimney that can be lined or at least an external wall (or roof) through which a flue can exit.
- Secondly, you must have room to store the fuel – wood fuel is cheaper if you can buy in bulk, ideally from a local supplier, or even better are able to grow your own.
You might choose a stove with back boiler if you are off the gas network, are attracted to the open flame, or simply prefer the idea of greater autonomy. Ideally, you would already have a thermal store (or space for one), as this would improve the efficiency of your heating system and allow a number of heating technologies to be linked.
For a pellet stove, you would also need an electrical connection near where the stove will be located, and the time and energy to maintain and load the stove – which is a lot less onerous for a pellet stove than wood burner, although wood burners will still work without electricity!
Biomass boilers - £7,000 to £15,000
fuel: 3-5p/kWh, CO2: 0.02-0.04kg CO2e/kWh
Biomass boilers come in three main types – log, chip, and pellet – and each has its advantages and disadvantages. As a general guide, log boilers are cheapest but need the most maintenance (daily) and fuel storage space. Pellet boilers can be fully automated, and need a lot less maintenance (monthly) - however they are more expensive and use the most expensive type of wood fuel. Wood chip boilers sit somewhere between the two, and are most often specified for district heating schemes due to the ease of production, transportation, drying, and storage of the chip.
Much like stoves above, biomass boilers require a flue and plenty of space – the appliance itself is much larger than a gas boiler and requires regular access.The fuel storage will need to be several cubic metres, depending on how much heat demand you have and how often you’d prefer deliveries. You will also need a thermal store, which means that you can link in other forms of renewable heating such as solar thermal, enabling the boiler to be turned off during the summer.
You probably won’t need planning permission to install a wood-fuelled boiler, but always check with your local planning authority or installer nonetheless. Generally:
· Flues must be no more than a metre above the highest part of the roof.
· Flues are not permitted on the principal or side elevation if it would be visible from a highway in a conservation area or World Heritage site.
· You may need special consent if your building is listed or in a designated area
· In Scotland, the flue should not be in an Air Quality Management Area.
If the boiler or fuel store requires a new building, the same rules apply as for any other extensions and outbuildings – see the Planning Portal for guidelines on planning permission for biomass systems.
All new wood heating systems do have to comply with building regulations.If you use an installer who is a member of a Competent Person Scheme such as HETAS, this process is made much easier - they will certify that your system is safe and legal, and there will be no need for you to contact the local building control office. See the Government’s list of current schemes.
Important: Both the system and the installer must be MCS accredited for you to be eligible for RHI payments. Also check that the installers are members of the Renewable Energy Consumer Code (RECC) who agree to abide by its strict Consumer Code.
Note: If you live in a smoke control area, you will need to use an exempt appliance. These are available for all types of wood heating system. To find out whether you are in a smoke control area, contact the Environmental Health or Protection department of your Local Authority.