Fuels for biomass boilers

In horticulture, the most popular fuels used are woodchip, straw and (for small systems) wood pellets. We compare the characteristics of each type and discuss general fuel issues.



Calorific value

Bulk density


• To maintain consistent quality, you can specify chip grade:

── G30: (10–30 mm edge length and <30% moisture content)

── G50: (30–50 mm edge length and <30% moisture content)

── G100: (50–100 mm edge length and <30% moisture content)

• Woodchip is a popular fuel at the moment




• Usually in Heston bales weighing 600 kg

• Moisture content <20%

• Check inside for mould

• Biggest issues with straw are emissions and quality



Wood pellets

• Easiest material to handle, but expensive

• The domestic RHI may cause wood pellet supply to become limited as it will be householders’ fuel of choice



Main issues with any type of fuel

  • Cost
  • Good long-term availability
  • Consistent quality
  • Emissions and residues

As might be expected, straw is cheap but can be problematic in terms of quality and emissions. High-value wood products are easier to handle, more consistent and burn more cleanly.

Storage of fuel is a significant area of concern for many greenhouse growers, as space is often limited. The larger the storage space available, the more opportunity there is to buy in bulk and keep fuel costs low.

However, fuel suppliers are willing to enter into contracts that guarantee a regular supply of chips and a week’s worth of storage is often sufficient.

Useful links

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Nathalie Key

Research and Knowledge Exchange Manager

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