Biomass Boilers

Wood-fuelled heating systems, also called biomass systems, burn wood pellets, chips or logs to provide warmth in a single room or to power central heating and hot water boilers.

A stove burns logs or pellets to heat a single room – and may be fitted with a back boiler to provide water heating as well. A boiler burns logs, pellets or chips, and is connected to a central heating and hot water system. A wood-fuelled biomass boiler could save you up to £800 a year compared to electric heating.

The benefits of biomass heating

1. Affordable heating fuel

Although the price of wood fuel varies considerably, it is often cheaper than other heating options.

2. Financial support

Wood fuel boiler systems could benefit from the Renewable Heat Incentive (RHI)

3. A low-carbon option

The carbon dioxide emitted when wood is burned is the same amount that was absorbed over the months and years that the plant was growing. The process is sustainable as long as new plants continue to grow in place of those used for fuel. There are some carbon emissions caused by the cultivation, manufacture and transportation of the fuel, but as long as the fuel is sourced locally, these are much lower than the emissions from fossil fuels.

If you live in Scotland, view case studies and examples where homeowners have installed a wood-fuelled heating system.

Costs, savings and financial support

Maintenance

Biomass boilers and stoves should be kept clean and swept regularly to remove ash. Ash quantities are generally very low (less than one per cent of fuel volume), but you will still need to empty the ash bin of a wood burning stove or boiler. This is likely to be weekly and never more than once a day. A log fire requires ash removal before every use.

Some appliances, particularly boilers, have self-cleaning systems which will collect ash from the combustion grate and the heat exchanger tubes. If there is no automatic ash cleaning mechanism in place the boiler will need to be shut down periodically so that this can be done by hand. If the ash is not cleaned out regularly, it will build up and adversely affect combustion conditions, which can lead to boiler failure and shut down. Some boilers have a mechanism for compressing the ash which reduces the number of times the ash bin needs to be emptied.

With automatic ash removal and cleaning of the heat exchanger the only other maintenance requirement will be occasional ash removal and an annual maintenance check. If you have a wood burning stove or boiler the chimney and flue pipe must be swept regularly to remove all soot deposits and prevent blockage. HETAS recommend that this “should be done at least twice a year, preferably before the heating season to check that the flue has not been blocked by bird’s nests for example and also at the end of the heating season to prevent soot deposits from resting in the chimney during the dormant period”.

Further information on chimney safety can also be found in the National Association of Chimney Sweep’s leaflet Heat your Home Safely. Burning wet wood increases the amount of soot in a chimney and with it the chance of a chimney fire. Logs should always be seasoned (air-dried) for at least a year before being burned.

Choosing a wood-fuelled heating system

Boiler or stove?

Boilers can be used in place of a standard gas or oil boiler to heat radiators for a whole house, and to heat the hot water. Stoves are used to heat a single room, usually in conjunction with other heating systems, but may also have a back boiler to provide hot water. Stoves are not eligible under the domestic RHI unless it is a pellet stove with a back boiler.

Chips, pellets or logs?

Chips are used to heat larger buildings or groups of houses.

Pellets are much easier to use and much more controllable than logs. Pellet boilers can run automatically in much the same way that gas or oil boilers operate. Most pellet and chip burners use automatic fuel feeders which refill them at regular intervals.

Log-burning stoves and boilers have to be filled with wood by hand and require considerably more work. You will need a lot of logs to heat a whole house, but they can be cheaper than pellets if you have a good local supply.

Do you have a local fuel supplier?

Some companies now offer deliveries of pellets anywhere in mainland Britain and Northern Ireland while the supply of logs is more variable.

Do you have space?

Wood boilers are larger than gas or oil equivalents and you will need space to store the fuel. This area will need to be somewhere that’s handy for deliveries as well as appropriate for feeding the boiler.

Do you have somewhere to put the flue?

You will need a flue which meets the regulations for wood-burning appliances. This could be a new insulated stainless steel flue pipe or an existing chimney, though chimneys normally need lining to make them safe and legal.

Get in touch

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