An energy supplier should sell wood pellet and woodchip fuel per ton. However, in some cases you could have the option  from your energy supplier to provide heat (instead of fuel).

Considerations when purchasing fuel:
Chlorine and other contaminants such as paint and creso can cause the boiler to burn at a higher than recommend temperature, reducing the lifespan of the boiler. Other containments such as nails and metal can also damage the boiler. As a rule of thumb, the lower the moisture content of the fuel, the more efficiently it will burn, as burning water has no heat benefit. The ash content of the fuel effects how regularly the boiler needs to be cleaned.