Biomass Boilers

Biomass heating is a ‘low-carbon’ technology and is both sustainable and renewable.

 

Heating a single room using a wood burning stove – or a whole property using a wood-fuelled boiler – is known as biomass heating. Biomass can usually be integrated into a home’s existing heating and hot water system and can be an attractive option for households with a reliable wood supply, reasonable storage space and delivery access.

 

Because the CO2 absorbed by the trees when they are growing is approximately the same as the CO2 released when the fuel burns they are considered to be ‘low carbon’. They are not ‘carbon neutral’ or ‘zero carbon’ because there are still carbon emissions associated with the fuel’s extraction, processing and transportation.

 

TWO MAIN TYPES OF BIOMASS HEATING APPLIANCE

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1) Stoves: These burn logs or pellets to provide space heating for individual rooms. Stoves can also be fitted with a back boiler to provide hot water for the kitchen and bathroom. Stoves are usually around 7kW and have an efficiency of between 60-80%.

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2) Boilers: Larger and more industrial in design, these provide whole house heating and hot water. Domestic log boilers range from 20-50kW and are stoked by hand. Pellet boilers range from 8-30kW and often incorporate a pellet hopper, which automatically feeds the boiler with fuel.  Chip boilers are most efficient for larger (50kW+) systems so are generally not suitable for individual domestic properties. Some biomass boilers are designed to take a variety of wood fuels, including logs, chips and sawdust, and might be viable if you have access to a range of different wood sources.

 

 

There are three main types of wood fuel that can be used in domestic systems:

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Logs
Logs require little processing except for seasoning (drying out). This process can take up to 3 years and brings their moisture content down to about 20% meaning the logs burn hotter and produce less smoke. Logs are usually cheaper than other types of wood fuel but need more space for storage and can only be used in manual feed boilers or stoves.

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Wood chips
These are sourced from forestry ‘thinnings’ or made from untreated waste wood. Wood chips are typically used in larger heating systems such as those found in schools or blocks of flats. When they are used in smaller (e.g. domestic) systems the chips must be produced to a standard size and with low moisture content.

 

Pellets
Wood pellets are made from by-products such as saw dust and have a low moisture content of between 8-10%. As a consequence they are more energy-dense than logs or chips and require about a third of the storage space. The uniform shape makes pellets ideal for automated systems.

 

 

COST & SAVINGS

 

The initial cost of installation depends on the size and type of system: a log burning stove might be in the region of £2,000; a stand-alone pellet stove around £4-4,500; and an auto-feed pellet boiler for an typical family house around £11,500. You should allow for a further £100 to £200 per year for annual maintenance for a boiler.

The financial and CO2 savings you will make from your biomass system will vary depending on what fuel you are currently using for heating your home. If you’re using electricity or oil biomass will save more than if you’re using mains gas. And ensuring your property is fully insulated will reduce your heating demand and mean you can fit a smaller and cheaper system.

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The following table shows potential financial and CO2 savings for a 3 bedroom semi-detached property with loft and cavity wall insulation: