Pellet stoves and boilers

2013478big.jpgPellets offer a clean, free flowing, relatively high energy density fuel that can be conveniently delivered by tanker via a long hose.

Pellets offer a great deal ofconvenience compared to other types of biomass fuel. Buildings using pellet boilers often have their fuel delivered by lorries (similar in appearance to an oil tanker) able blow fuel directly into a store. Smaller appliances, such as a stoves with integral fuel hoppers, may be better served by bags containing 10 to 25 kg of fuel. Compared with logs and chips, pellets have a high energy density which means that less storage space is required. Pellet systems are often physically smaller than their log and woodchip counterparts.

Pellet stoves

Pellet stoves fulfil a similar role to their log fired counterparts. They are available in a range of sizes from small room heaters to larger units incorporating a boiler able to supply heat to a few radiators or a domestic hot water systems. They usually have an integrated fuel hopper which is filled from a bag. Pellet stoves are available from room heaters of 1.5 to 2kW up to around 12kW, above this size a boiler is more appropriate (see below). Some are equipped with timers, remote controls or even systems using text messages to start and stop operation to ensure you always come home to a warm room.

Things you should know

  • All pellets are not the same. Many types of biomass can be pelleted including straw, miscanthus, and cotton waste. While these alternative feedstocks can be useful, it is important to remember that different fuels have different chemical composition and burning characteristics. If your pellet stove has been designed and set up for wood pellets, you should only use wood pellets or risk damaging the stove and voiding the warranty.
  • While you are able to order pellets in small 15kg bags, you will pay a premium for small orders. If you have the space, it will be more economic to order larger quantities at a time.
  • Are your pellets good quality? Pellets are prone to turning to dust if they get wet or crushed, this will tend to jam in your stove and put it out.
  • Are you in a smokeless zone? If you are and you want to burn wood then your choice of stoves will be restricted to approved appliances (Further information is available here)

Pellet boilers

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.

It is very important to ensure that pellet fuel stores are well sealed and do not allow dust to enter the boiler room or other parts of the building. Guidance on designing afuel store is available here (PDF -2.6 MB), and there is more information in thepellet stores section

Things you should know

  • All pellets are not the same. Many types of biomass can be pelleted including straw, miscanthus, and cotton waste. While these alternative feedstocks can be useful, it is important to remember that different fuels have different chemical composition and burning characteristics. If your pellet stove has been designed and set up for wood pellets, you should only use wood pellets or risk damaging the stove.
  • While you are able to order pellets in small 15kg bags, you will pay a premium for small orders. If you have the space, it will be more economic to order larger quantities at a time.
  • Are your pellets good quality? Poor quality pellets are more prone to turning to dust if they get wet or crushed, and this will tend to jam in your stove and put it out.
  • Are you in a smokeless zone? If you are and you want to burn wood then your choice of stoves will be restricted to approved appliances (Further information is available here)