What is biomass?
We are all familiar with the idea of a log fire as a means of keeping warm. The term, ‘biomass’, when used in the context of heating, is simply to do with burning anything that has been grown in a human timeframe, as opposed to fossil fuels, which are derived largely from plant matter buried in the strata of the Earth millions of years ago.
Burning biomass is close to carbon neutral, as the CO2 released on combustion is only that which was taken from the atmosphere in order for the plant to grow. However, burning fossil fuels releases carbon that has been buried for millions of years, and hence adds to atmospheric CO2 and global warming.
The use of biomass for central heating and hot water can save you money on your fuel bills and will qualify for the governments Renewable Heat Incentive which can reduce pay back times on domestic systems to 7 years or less. The costs of new systems range in price but start at around £7,000.
How can I use biomass for heating?
1) Open fire
This has been the main method of heating buildings for centuries, either using wood or coal. The problem with this method is the inefficiency – only about 20% of the calorific value of the fuel ends up as heat within the building. This can be increased slightly by various modern baffle systems, but the upper limit will be about 30%. So at least 70% of the heat goes straight up the chimney.
2) Wood burning stove
These basically operate as room-heaters in the same way as open fires. The difference is that stoves are enclosed, and the air supply can be controlled, leading to efficiencies in excess of 80%. This means you can get the same amount of heat as you would from an open fire using a quarter of the logs.
Some stoves have a back-boiler to heat domestic hot water (DHW). Whilst log burning room heaters do not qualify for government tariffs, wood burners are an effective way to heat your house. If you are interested talk to us as we have an approved installer.
3) Wood burning central heating
Central heating boilers come in many forms, such as:
- A simple range (e.g. Rayburn) with a boiler to supply radiators and hot water.
- Log fired central heating boiler and accumulator tank (heat store) – the aim here is for a quick efficient burn to heat the water in the tank – the central heating is then run from the tank using normal heating controls. When the temperature drops to a certain point, another burn is required.
- As above, but using pellets as a fuel. This is often an automated process with pellets fed from a hopper into the boiler.
These systems can take up a lot of space, with tanks often in excess of 1000 litres.
What fuel is used?
The main fuels used in a domestic situation are logs and wood pellets but wood chip can also be used in some larger systems. Logs are generally about half the price of pellets (per unit of heat) – and pellets are less expensive than heating oil.
Logs require a considerable amount of storage space to ensure you have enough in stock to allow adequate drying time. Moisture content should be reduced to 20% for efficient burning, otherwise some of the calorific value of the wood will be used to drive out moisture, thus reducing the effectiveness of the heating.
As an example, a Rayburn supplying 15 radiators can get through 9 tonnes of logs in a 7 month heating season – this requires 15m3 of storage. Ideally you should have storage for 2 heating seasons for best efficiencies. The other downsides are that you have to stay well ahead in your fuel buying (or cutting), and the whole process requires a degree of labour. On the plus side, you can heat your house for half the price of oil (or free if you have your own supply of wood and time to process it).
Pellets come ready to burn, and the only reason to buy in bulk is for cost savings. Current pellet prices are around 20% less than oil.
The main issues are the hands on nature of the process – less in the case of pellets, but a certain degree of maintenance is still required – such as removing ash.
- Biomass fuel is plant-based material grown during our lifetime, such as logs, wood pellets, willow faggots, miscanthus briquettes, as opposed to fossilised plant-derived fuel like oil or coal.
- Currently the most commonly used biomass fuels used are logs and wood pellets. Wood pellets can be easier to handle and store, but are more expensive than logs, though less expensive than oil.
- Traditional log fires use biomass, but at least 70% of the heat goes straight up the chimney – wood burning stoves and biomass boilers are more efficient, with only around 10 to 20% going up the flue.
- You can run radiators, central heating, or heat water using biomass.
- Biomass is basically carbon neutral – though there might be some minor carbon costs in transportation or processing.
- If you are considering a Biomass installation the Renewable Heat Incentive may apply.