Wood Chips

Wood Chips

For boilers like the Guntamatic Powerchip or the Lindner & Sommerauer SL30-150kW and SL199- 250kW it’s our recommendation to use G30 and G50 wood chips. This means chips that have an average size of 30mm, plus a maximum of 30% moisture content. Wood chip dryness is key for getting the most out of your biomass boiler. 

If you are buying wood chips in, be sure that they are of the highest quality (as set out by the assurance scheme run jointly by HETAS and Woodsure). The grade and moisture content of your wood chips should be outlined on your delivery paperwork. 

To find suppliers, check out the Biomass Suppliers List (BSL). We’ve found this to be the most comprehensive list of biofuel suppliers in the Wye Valley and across the UK. 

If you can, we would always recommend checking the wood chips at the point of delivery. We’ve got a handy guide to inspecting woodchip quality here.  

Chipping Your Own Fuel

This is where you can reach your maximum savings! If you have your own logs, a contract chipping service (check out the Biomass Suppliers List (BSL) again for chipping services) can process 15-20 tonnes per hour. This means that you can a good few months' supply chipped in one go and fuel cost savings of up to 80% versus fossil fuels. 

Chipping wood for biomass boilers

Alternatively, if you have your own woodland, you can sell your wood back to the supplier in return for a discount on your fuel. 

If you are using your own wood, make sure it is seasoned appropriately so that it has a maximum moisture content of 30% (before chipping). You can season logs by storing them raised from the ground, covered in a tarpaulin which is open at each end in order to air dry. You’ll find that wood has less of a tendency to reabsorb water once it begins to season. 

You need to use a fuel grade chipper that has set screens so that you can produce the right size of chips. So a general agricultural chipper which is essentially a shredder might not do the job. Make sure that the chipper you use is able to process to G30 or G50, that's an average chip size of 30-50mm.

chipping wood for biomass boilers


When it comes to storing your wood, go for the largest covered and enclosed area you can possibly build or convert and existing space from, so you can store the maximum amount of fuel. Make sure you have access through a hatch so that you can regularly inspect the quality and that the floor of your store is level with agitator sweep arms. 

You will also need to clear out the store annually, to make sure stones or other foreign objects have not worked their way in. The best time can be during summer when your boiler is not needed quite so much. 

Check out the grants available from the Forestry Commission to see if you can get any help with the management and development of your woodland. 

And finally, take a look at the table below to explore how wood chips perform, compared to other sources of fuel:

Fuel kg/m3 g CO2/kWh kWh/ Kg
Wood Chips 250 7 3.5
Logs 350 7 4.1
Wood Pellets 650 15 4.8
Coal n/a 484 8.6
LPG n/a 323 6.6
Heating Oil n/a 350 10
Electricity n/a 530 n/a
Source: Biomass Energy Centre