The simplest way of using many forms of biomass for energy is simply burning it. Doing so in an enclosure, in which the airflow is restricted, will be far more efficient than burning it in the open. This enclosure can be used to provide heat for the room it stands in (a stove) or, by heating water and pumping it through pipes, it can provide heat to several rooms, and/or domestic hot water .This can even be extended to provide heat to several buildings from the same boiler, which is known as district heating.
Pellet boilers tend to be physically smaller than chip fired equivalents as less robust feed and burning systems are needed. Installations are available from around 15kW upwards, there is no significant technological upper limit to installation size (there are a number of power stations in Europe that run exclusively on pellets.)
Pellet boilers are available with either a built in hopper, filled manually from bags, or with a separate, bulk storage hopper. The latter allows pellets to be delivered by tanker, down a long pipe, typically just once a year, with the minimum of disruption. Buying in bulk is also cheaper, provided a minimum order size can be achieved, but the additional cost of a bulk hopper, and pellet feed to the boiler may not be justified.