Pellet Stove - Principles of Operation

Principles of Operation

A pellet stove normally consists of these components, whether basic or complex:

• A hopper
• An auger system
• Two blower fans (combustion and convection)
• A firebox (burn-pot and ash collection system), sometimes lined with ceramic fiber panels
• Various safety features (vacuum switch, heat sensors)
• A main control box/board

To properly function, a pellet stove uses electricity and can be plugged into a normal wall outlet. A pellet stove, like an automatic coal stoker, is a consistent heater consuming fuel that is fed evenly from a refillable hopper into the burn-pot (a perforated cast-iron or steel basin), through a motorized system. The most commonly used distributor is an auger system that consists of a spiral length of metal encased in a tube. This mechanism is either located above the burn-pot or slightly beneath and guides a portion of pellet fuel from the hopper upwards until it falls into the burn-pot and begins to combust.

Fan systems are necessary for clean, economical performance. The flame produced is concentrated and intense in the small area of the burn pot as a combustion blower introduces air into the bottom of the burn-pot, while also forcing exhaust gases up and out the chimney. While some pellet stoves will be hot to the touch (especially on the viewing window), most manufacturers utilize a series of cast-iron or steel heat exchangers that run along the back and top areas of the visible firebox. With a convection blower, room air is circulated through the heat exchangers and directed into the living space. This method allows for a much higher efficiency than the radiant heat of a hand-fed wood or coal stove, and will in most cases cause the top, sides and back of the stove to be not more than warm to the touch. Along with convection air, an exhaust fan forces air from the firebox through special venting specifically made for pellet fuel. This cycle of circulation is an integral part of the combustion system as well, for the concentrated high-temperature flame will quickly overheat the firebox. The possible problems associated with overheating are electrical component failure and flames traveling into the auger tube causing a hopper fire. As safeguards, all pellet stoves are equipped with heat sensors, and sometimes vacuum sensors, enabling the controller to shut down if an unsafe condition is detected.For maintenance (daily cleaning) it is best to use an ash vac. These are similar to shop vacs, but are designed for the removal of ash materials. These vacs are available with a pellet stove kit which enables the cleaning of the interior areas of the stove which improves efficiency.

Pellet stoves can either be lit manually or through an automatic igniter. The igniter piece resembles a car's electric cigarette lighter heating coil. Most models have automatic ignition and can be readily equipped with thermostats or remote controls.