Biomass wood heating

Biomass Heating Options

Biomass describes anything which grows, but most of the time biomass heating refers to the burning of wood products, for example logs, wood pellets, wood chips or briquettes. As long as something grows in the place of a harvested tree, as almost invariably does, there is virtually no adding of greenhouse gas to the atmosphere in the long run, unlike when burning oil, coal or gas (which also require much processing and transportation).

Types of Biomass heating:

Room heaters

1)      Wood burning stoves – An open log fire is made hugely more efficient if replaced by a log stove, delivering perhaps 70% of the wood’s heat energy to the room rather than 20-30% and drawing far less cold air into the building as flow up the chimney is very restricted, reducing draughts.

2)      Automated wood pellet room heaters – these are hand-filled every few days with wood pellets and controlled by timer and thermostat to warm the room as and when required. They have a visible living flame but are very quiet and can also heat radiators and/or a water tank (although they then need refilling much more frequently).

Central heating systems      

1)      Log, or ‘batch’ boilers – these are filled with very dry logs or strawbales once to three times daily to quickly heat a large tankful of water (a thermal store) which in turn supplies the radiator circuits in response to a timer/programmer and thermostats, for as long as the stored heat lasts.

2)      Automated chip or pellet boilers – these have large fuel silos within 15m of the boiler, drawing the fuel in as required and behaving otherwise like a conventional oil or gas boiler. Some can only run on pellets, often fed through flexible pipe using a suction pump, whilst others can use chips or pellets, with a heavy duty auger between silo and boiler.

What are the differences between wood pellets, wood chips and logs?

The principal pros and cons of the three fuel types are as follows:

Logs – log systems have fewer wearing parts and are simpler and cheaper to install. The downside is that handling the logs requires MUCH more labour time on a daily basis. This is OK if the house to be heated is of small-to-average size, or if you have a constant supply of free labour on site, but it is the reason why many such systems are regretted.

Chips – The advantages of chip systems are that they require much less regular intervention than log systems – they can be left alone for up to a month at a time – and that they can be supplied from local sources, making you independent of world energy markets and price fluctuations. They are ideal for landowners with commercial forestry near their homes as use of low value wood for heating can justify the cost of thinning and other beneficial forestry management operations. Chip systems suit large heat demands such as very large houses and/or groups of dwellings and/or commercial buildings which can be served from a shared boiler in a ‘District Heating Scheme’, as large fuel cost savings are necessary to justify the high cost of the fuel handling equipment.

Pellets – wood pellets are a highly processed product, very dry and dense, which flow a bit like a liquid and take up a quarter of the space of chip with the equivalent heat content. As a result the storage and handling equipment is much cheaper and more compact which makes it more suitable where heat demands are more modest and/or there is less space available for storage or for the manoeuvring of delivery vehicles. A blower delivery lorry must get to within around 15m of the pellet store, whilst a chip trailer needs to be able to tip its full load over a lip into a hopper within a few metres of the boiler house.

Is my house suitable?

When considering which biomass boiler system is most suitable for your home, the main issues to consider are: –

  • Fuel supply – The fuel supply must be reliable for the foreseeable future. Logs and chips are too bulky to be transported more than a few miles economically, whilst pellets can be shipped around the world making them a global commodity, without much effect on their bulk cost or environmental impact. Obtain quotes for fuel delivery, chipping, etc, as appropriate, and discuss delivery methods, width or height restrictions, turning space requirement and even cleaning/de-ashing services, before making any purchasing decision. Wood fuel suppliers must guarantee minimum quality standards relating to moisture content, particle size, etc.
  • Heat cost – the relative costs of the different heating fuels is estimated in the table below, compared with equivalent costs, allowing for boiler efficiency and servicing costs for a 3-bedroom detached house in Scotland, from the April ’13 Sutherland Tables.
Fuel TypeCost Per KwHCost Per Year
Wood Pellet5p£1,068
Wood Chip3.5p£1,141
Mains Gas7.4p£1,356
Night Storage Electricity8.1p£1,748

How much does it cost?

The cost of a professional biomass boiler installation is dependent on the property, fuel choice and location and ranges from about £600 to £1,200 per kW of peak heat output, excluding the cost of the heat distribution system (eg. underfloor heating).

The installed cost of a typical 40kW system, for example, would be in the region of £36,000 plus the cost of the distribution system. The price per kW gets lower as systems get larger.

What are the advantages?

By harnessing a sustainable resource, a biomass boiler has much lower CO2 emissions. A good system causes at least 90% less CO2 emission than an equivalent oil boiler.

A well-designed system in an energy-efficient dwelling will cost less to run than any other at current fuel prices. An approximate running cost comparison per kWh and per year for a typical 3 bed detached house in Scotland are shown in the table above. (Note that, as explained above, a chip boiler would not be appropriate for such a building on its own due to high fixed capital costs for small installations).

Using a local heating fuel source can insulate you from the sometimes wild fluctuations in heating costs experienced by oil and gas systems, caused by political and other influences on global markets.