Biomass is organic matter of recent origin. It doesn't include fossil fuels, which have taken millions of years to evolve. The CO2 released when energy is generated from biomass is balanced by that absorbed during the fuel's production. We call this a carbon neutral process.

Biomass is often called 'bioenergy' or 'biofuels'. These bio fuels are produced from organic materials, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products. Bio fuels fall into two main categories:

Woody biomass includes forest products, untreated wood products, energy crops, short rotation coppice (SRC), e.g. willow.

Non-woody biomass includes animal waste, industrial and biodegradable municipal products from food processing and high energy crops, e.g. rape, sugar cane, maize.

For small-scale applications of biomass the fuel usually takes the form of wood pellets, wood chips and wood logs.

Biomass and your building
There are two main ways of using biomass to heat a property:

Stand-alone stoves providing space heating for a room. These can be fuelled by logs or pellets but only pellets are suitable for automatic feed. Generally they are 6-12 kW in output, and some models can be fitted with a back boiler to provide water heating.

Boilers connected to central heating and hot water systems. These are suitable for pellets, logs or chips, and are generally larger than 15 kW. Stoves can be 80% efficient. They're normally used for background heating. They also add aesthetic value in the living area of the house itself.

Many wood burning stoves act as space heaters only. But the higher output versions can be fitted with an integral back boiler to provide domestic hot water and central heating through radiators, if needed.

There are many domestic log, wood-chip and wood pellet burning central heating boilers available. Log boilers must be loaded by hand and may be unsuitable for some situations. Automatic pellet and wood-chip systems tend to be more expensive. Many boilers will dual-fire both wood chips and pellets, although the wood chip boilers need larger hoppers to provide the same time interval between refuelling.

Boilers can be designed with an integral hot water energy storage or accumulator tank that stores water up to 90º C, enabling the supply of heat to be further decoupled from the combustion of the fuel. This is particularly helpful with log boilers where systems operate at full load and the matching of demand with load is performed by the accumulator.