Pellet Stove and Boiler Introduction
Many consumers are under the impression that pretty much all pellet stoves and boilers have the same capabilities, and that every pellet stove and boiler will burn every type of wood pellet fuel. Well this simply isn't the case, and the pellet stoves and boiler which will have complications are the most common. The reason for this is very simple, it is much cheaper and easier for pellet stove manufactures to design and build their pellet stoves and boilers with certain burn pots, pellet fuel hoppers, pellet feed augers and thermal heat exchangers.
All pellet stoves and boilers are designed to burn premium grade wood fuel pellets. Premium grade pellets if produced to the required standard should have a maximum ash content of 0.5 and a consistent pellet length of below a half inch or around 13mm. Many pellet stove and boiler manufactures design their products to burn pellets which exactly meet these criteria. However their products will also generate complications, if the pellet fuel does not meet these exact criteria. As the characteristics of the fuel pellets from manufacturer to manufacturer do change, it is more than likely consumers will purchase fuel pellets that their pellet stove will have complications with. Therefore avoiding these wood pellet burner designs is crucial.
Another reason to avoid these poorly designed pellet stoves and boilers, is to avoid high pellet fuel prices. Premium pellets are the most expensive pellet fuel, and are the most susceptible to price increases and supply issues. Purchasing a more pellet fuel flexible pellet burner will enable you to have choice over the fuel which you use based on price and current supply and availability. This includes other grades of wood pellet fuel and the growing number of biomass fuel pellets which are being developed which cost around half that of premium wood pellet fuels. Examples are switchgrass, miscanthus, willow, wheat straw and hemp pellets. One of the key components in the pellet stove or boiler which effects what type of pellet fuel the unit can or cannot use without complications in the pellet burner burn pot.
Below are 2 examples of burn pot designs
Wood Pellet Stove and Wood Pellet Boiler Burn Pot Designs
The design of the burn pot is crucial for efficient and flexible pellet fuel combustion. The core requirements of the burn pot are to maintain efficient continuous combustion while removing ash or clinker formations post combustion. Clinker formations are where ash generated reaches a high enough temperature to melt together and form a solid 'glass like' mass.
The Common and Most Limited Wood Pellet Burner Burn Pots
The two images above are of the most common burn pot designs found in wood pellet stoves and wood pellet boilers respectively. Though slightly different in appearance and design, the core design of both pellet burn pots is the same, a drop down pellet burner. As stated, the more common and most basic designs of pellet burn pots found in pellet stoves and boilers is designed purely to burn premium wood pellet fuel. The pellets are fed from above, and fall down into the combustion area. Air is fed into the fire, and the fan is also used to remove ash.
Here is the core problem with this design of burn pot. The fan which provides the air for combustion is also responsible for removing ash. Air speed for combustion remains fairly constant for all forms of wood and biomass pellet fuel. However, the amount of ash generated can range from 0.5% up to around 7%. Therefore the fan cannot remove sufficient ash for other grades of pellet fuel other than premium wood pellet fuel (0.5%). Increasing fan speed to remove more ash would reduce combustion efficiency, and still has no chance of removing any heavy clinker formations. The guide will show you which burn pots to look out for and much much more, including the different heat exchanger designs and grading pellet fuel.