SuperHomes

Biomass boilers

Biomass is a renewable energy source, generated from burning wood, plants and other organic matter.

Biomass heating systems burn logs, pellets or chips, to provide warmth in a single room or your whole house. Biomass boilers can replace oil or gas boilers to heat hot water and radiators (or under floor heating).

Advantages

  • reduce your carbon footprint
  • reduce energy bills
  • heat your home and water
  • some financial return

Biomass boilers are generally more suitable for people not connected to mains gas.

The boiler will need a flue designed for wood fuel (existing chimneys can be lined).

You will also need space. Biomass boilers tend to be larger than the gas or oil equivalent. And you need about 6-7 cubic metres of space near where the boiler is sited to store the fuel (for an average size house). Biomass boilers can burn logs, wood chips or pellets. If you’ve got space for a large fuel store you can reduce costs by having fuel delivered in bulk. Ideally the fuel storage area will be under cover, as it is important to keep fuel dry. High moisture content in the fuel will reduce the efficiency with which it burns (and increase the risk of a chimney fire and undesirable emissions) and if wood pellets get wet, they turn to unusable mush.

Your property also needs to be accessible for a fuel delivery lorry.

And it is important to check that the boiler will work with your existing plumbing.

It’s important to think through carefully the supply, storage and handling of fuel before you invest in a biomass boiler. There are generally some trade-offs between each fuel type, and they will be specific to your site

Wood pellets are made from compressed sawdust and wood shavings and other biomass products and are uniform in size and shape. They have higher energy content and so take up less storage space than logs or wood chips. Boiler manufacturers specify the size, shape and moisture content their products need to perform well. Wood pellet systems are the smallest, neatest and most like a mainstream boiler and require the least input from the user.

Log-fed boilers are more suitable for people with ready access to a supply of wood, and time to cut it to the right size. Logs must be manually fed into the boiler and the process is less automated, depending more on human input.

Woodchips are cheaper and more abundant than pellets, but some woodchip boilers need woodchips of a very specific size and moisture content, so not all woodchips are suitable. They allow for more mechanisation than logs but are not as efficient as wood pellets and are really only suitable for larger or multiple properties due to the capital costs (which include the cost of providing dry storage and a system for mechanically feeding the woodchips into the boiler).

As part of the Clean Air Strategy, government has pledged that from spring 2021 all wood sold in units of less than 2m3 with a moisture content of more than 20% will be banned, in an attempt to encourage owners of stoves and open fires to move to ‘cleaner’ alternatives such as dried wood, which cause less pollution. The Ready to Burn certification scheme will come into force in England from 1 May 2021 for most wood suppliers

Biomass boilers should be kept clean and swept regularly to remove ash. This is likely to be weekly and never more than once a day, If the ash is not cleaned out regularly, it will build up and adversely affect combustion conditions, which can lead to boiler failure and shutdown.  

Some boilers have a mechanism for compressing the ash, which reduces the number of times the ash bin needs to be emptied. Others might have self-cleaning systems. If there is no automatic ash cleaning mechanism in place, the boiler will need to be shut down so that this can be done by hand. 

You should also have an annual maintenance check carried out on your boiler, and 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 and at the end of the heating season. 

Logs should always be seasoned (air-dried) for at least a year before being burned. Burning wet wood increases the amount of soot in a chimney and with it the chance of a chimney fire.  

According to the Energy Saving Trust, to install an automatically fed pellet boiler in a typical home costs between £11,000 and £17,000.

Unlike other renewable technologies there is also an ongoing fuel cost with biomass heating.

Wood pellet costs will depend on the size and method of delivery. If you have room for a large fuel store that will accept several tonnes of pellets at a time and be delivered in bulk you can generally reduce the cost, compared to bagged pellets.

Logs are cheaper and if you can buy them unseasoned and store them somewhere where to season you can save money.

Suppliers’ costs will likely vary according to the distance the supplier has to travel. Make sure there is at least one, or preferably a choice of, local fuel suppliers

Biomass systems are deemed permitted developments unless the flue exceeds the height of the roof by one metre or more. You will also need to make sure that your installation meets the standards of the relevant building regulations on clean air, ventilation, noise and safety.  

Contact your local planning department for all installations to check conditions will be met. 

Renewable Heat Incentive 

Biomass boilers are eligible for the Renewable Heat Incentive (RHI).

Your system must provide some space heating, must meet air quality standards, and you must buy fuel from a supplier on the Biomass Suppliers List found here