Woodchip boilers

Woodchip fuel is suited to larger scale systems, and can be particularly useful on sites that include areas of woodland.

Woodchip boilers

Wood chip boilers are most appropriate for medium and large scale installations. Buildings that currently use wood chip boilers include blocks of flats, visitors centres, office buildings and even airport terminals. It is very important to ensure that wood chip boilers are supplied with the appropriate type of fuel. This will vary between boiler types and sizes. The two most important variables are particle size and moisture content. Wood chips that are too large or too wet for example, can jam the fuel feed system, reduce the efficiency and reliability of the boiler or cause the control system to trip out. More information about fuel standards can be found here.

Wood chips can be produced from round wood by using specialised wood chippers. These are designed to produce a uniform size of chip that works well in automated fuel feed systems. There is a large number of wood chip suppliers around the country, alternatively if the boiler is going to be installed on a farm or other site with its own woodland it may be possible to use this resource to provide at least part of the fuel requirement. The use of a specialist, contract chipper service can avoid the need to buy a chipper.

Since wood chips require less processing than pellets and less manual handling than logs, they can be an extremely energy efficient use of biomass. Country estates, farms and other sites where there is woodland near to the point of end use are particularly well suited to wood chip systems. Many of these sites also find that they are able to offset forestry and heating costs within the organisation.

Things you should know

  • System size - most chip boilers are quite large, they are available down to around 25kW, but most manufacturers don't produce systems below the 40kW mark.
  • Wood chips can be produced to different size and moisture content standards, are a highly variable fuel, you need to have a good idea of the fuel specification for your boiler and make sure it matches the fuel you have available.
  • Fuel containing contamination such as mud and stones can increase wear and tear on fuel feed and boiler components and well as reduce efficiency. Make sure the fuel you use is free from contamination. Due to processing methods, contamination tends to be more of an issue with chip than other fuel types. Fuel needs to be clean. Mud, stones, paints, varnish, other wood treatments, ply wood, chip board, etc. will have an adverse affect on your boiler and may well lead to increased wear, emissions, and reliability issues. Using treated wood as fuel could mean you are breaking the law. If you want to use treated wood make sure you comply with the waste incineration directive.
  • How will you feed the boiler? Have you considered transport and fuel delivery? The chip will probably be delivered in a large lorry and the most efficient way of unloading is to tip. Do you have appropriate access?
  • Design of the fuel store is critical and can form a significant part of the project cost. However additional expenditure at the outset can pay dividends for the lifetime of the store. Delivered fuel cost will often be influenced by the time taken to deliver, and the ability to accept fast delivery from an ordinary tipper truck will bring both lower price, and a greater choice of suppliers
  • Are you in a smokeless zone? If you are and you want to burn wood then your choice of boilers will be restricted to approved appliances (Further information is available here)


What's of interest

Biomass Heating: a guide to medium scale wood chip and wood pellet systems

Second in a series of a series of three technical design guides from the Biomass Energy Centre.  This guide covers larger scale systems (PDF - 5.0 MB)  N.B. Requires corrected Figure 19 below

Corrected low loss header diagram for guide to medium scale wood chip and pellet systems

This is required for guide above Figure 19, Pg 16 (PDF - 36 kB)