What are pellets?

Pellet is renewable and environmentally friendly solid fuel type in a form of cylinders made of biomass (most often wood one) compressed under high pressure. There are also pellets made of other plant biomass called agri-pellets that (e.g. straw pellets) have different features, including lower energy properties.

The English word “pellets” means small, rounded, compressed mass of a substance. To be precise, it is a shorted name for wood pellets. The main raw material source used for their production is waste from wood industry such as sawmill sawdust, shavings or chips. However, pellets can be produced from any type of plant biomass. It is highly energy-efficient fuel burnt in burners, ovens, boilers, fireplaces and other appliances. Some other names used are: “green coal” or “green energy” – pellet calorific value is within: 4.6 – 5 kWh/kg, 16 – 20 MJ/kg.

The specific pellet features are no emission of harmful gases during combustion and low amount of ash left after their combustion (up to 1%). Moreover, ash is an excellent, environmentally friendly fertilizer.

What are pellets made from?

The best quality wood pellet fuel is manufactured from clean sawmill sawdust, shavings and chips coming from wood with low content of resins, without addition of any adhesives. Pine, spruce, birch, beech, maple, oak, fir or willow wood is most often used for pellets. It is commonly believed that the best pellets are of light colour, produced from pine or spruce wood. Their colour informs of low bark content in pellets (bark may have some sand), which results in large ash content and lower calorific value.

Agri-pellets and pellets

Pellets produced from other biomass and agricultural production waste are called agri-pellets and have lower calorific value ranging from 12 to 17 MJ/kg, and amount of ash left after combustion is approx. 3 – 7%. Their advantage is price that can be twice cheaper than that of wood pellets. Agri-pellet production does not depend on the location of wood industry in particular area, which increases their availability. Individual customers, that heat residential buildings and appreciate comfort, usually select the highest quality wood pellets. Where economy is of key importance, pellets of worse quality and agri-pellets at more affordable prices are selected.

When selecting agri-pellet heating, it is worth to take care of the higher comfort of use, which can be ensured by purchase of the Revo series burner – high combustion efficiency and patented rotary combustion chamber system ensure permanent removal of ash.

How are pellets produced?

Wood pellets like briquettes are produced in the mechanical crushers. The pellet production process starts from raw material sorting and crushing into smaller parts. Good wood pellets do not contain any chemical additives. The only binder present in pellets should be natural resins contained in sawdust. The mass is extruded under high pressure through a die to produce pellets. The last stage of production is pellet cooling and packing. Pellets are most often produced in a form of cylinders in diameter from 6 to 8 mm.

Renewable energy – environmentally friendly. No damage to environment

During pellet and agri-pellet combustion, no harmful gases containing sulphur, chlorine or mercury are released into the atmosphere. CO₂ is released – gas absorbed by green plants that convert it into oxygen. Hence, the biological cycle comes full circle

Energy crop plantations of willow, rose, mallow and reed are already being established with agri-pellet production in mind. Those plants are characterised by intense green mass growth and they are processed into agri-pellets after cutting.

Why pellets?

By heating your home with wood pellets – you protect environment and save your own money.
In a few words:

Pellets are sold in 15 kg, 20 kg and 25 kg bags, 1 tonne Big Bags and in bulk.

What should you consider when buying pellets

When you buy pellets from a new supplier, you are advised to buy first a sample amount for testing. Large ash content and slag formation may indicate pellet production from worse quality raw material and addition of undesired adhesive substances. To solve a problem of lower pellet quantity, we have developed the REVO series burners – thanks to the advanced rotary combustion chamber technology, automatic removal of ash from the burner is ensured.
Pellets should be:

  • dry (7 -12% moisture content)
  • of uniform size
  • sold in air-tight plastic bags
  • free of dust, sawdust, bark or crushed pellets
  • with colour and smell similar to wood

The Pellas X burners are designed for operation with 6 – 8 mm diameter pellets.

Quality certificates of pellets

The certified pellets are warranty of their quality and comfort of use. Before 2011, there were no unified regulations concerning pellet quality in Europe. Only countries with the most developed wood industry and most widespread pellet heating system decided to introduce their own classifications. Pellets featuring the best properties have the following certificates:


  • ÖNORM M 7135
  • DIN 51731
  • DIN plus
  • SS 18 71 20 – Group 1
  • EN plus A1

Comparison of pellet standards and certificates


Pellet criteria Unit ÖNORM M 7135 DIN 51731 DIN plus SS 18 71 20 EN plus A1
Calorific value (Q) MJ/kg >18 17,5 16,5≤ Q ≤19 ≥16,9 16,5≤ Q ≤19
Moisture % <10 <12 ≤10 <10 ≤10
Ash % <0,5 <1,50 ≤0,7 <0,07 ≤0,7
Diameter (r) mm 4≤ r ≤10 4≤ r ≤10 6±1; 8±1 4≤ r ≤10 6±1; 8±1
Length (a) mm 5 x r <50 3,15≤ a ≤40 4 x r 3,15≤ a ≤40


Good certified pellets are more expensive, but they ensure:

  • Real pellet calorific value
  • Low ash content, rare need to remove ash and clean appliances
  • Low service cost