Pellet stove
Concept
A pellet stove is a stove that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces.Pellet stove takes biomass pellets as fuel to warm houses in harsh winter, It is commonly seen as the upgraded fireplace which has long been used since ancient times, in particular across Western countries. By slowly feeding fuel from a storage container (hopper) into a burn-pot area, they create a constant flame that requires little to no physical adjustments.
Pellet stoves are ideal for situations calling for a long, consistent burn that does not require restocking during the night. Useful in hoophouses or greenhouses under strict building codes that prohibit basic woodstoves.
Benefits
Pellet stoves are relatively versatile appliances. Most pellet stoves are self-igniting and cycle themselves on and off controlled by a thermostat. Stoves with automatic ignition can be equipped with remote controls. Recent innovations have created computer systems within pellet stoves which monitor various safety conditions, and can run diagnostic tests if an imminent problem arises.
A properly cleaned and maintained pellet stove should not create creosote, the sticky, flammable substance that causes chimney fires. Pellets burn very cleanly and create only a layer of fine fly-ash as a byproduct of combustion. The grade of pellet fuel affects the performance and ash output. Premium grade pellets produce less than one percent ash content, while standard or low grade pellets produce a range from two to four percent ash. Pellet stove users should be aware of the extra maintenance required with a lower grade pellet, and that inconsistent wood quality can cause serious effects to the electronic machinery over a short period of time.
A pellet stove is normally associated with pelletized wood. However, many pellet stoves will also burn fuels such as grain, corn, seeds, or woodchips. In some pellet stoves, these fuels may need to be mixed with wood pellets. Pelletized trash (containing mostly waste paper) is also a fuel for pellet stoves.
Unlike wood stoves which operate exclusively on a principle of chimney draft, a pellet stove must use specially sealed exhaust pipe to prevent exhaust gases escaping into the living space due to the air pressure produced by a combustion blower. Pellet stoves require certified double walled venting, normally three or four inches in diameter with a stainless steel interior and galvanized exterior. Because pellet stoves have a forced exhaust system, they have the advantage of not always requiring a vertical rise to vent, although a three to five foot vertical run to induce some draft is recommended to prevent leakage in the case of a power outage. Like a modern gas appliance, pellet stoves can be vented horizontally through an outside wall and terminated below the roof line, making it an excellent choice for structures without an existing chimney. If an existing chimney is available, manufacturers urge use of a correctly sized stainless steel liner the length of the chimney for proper drafting. Modern building techniques have created tighter sealed homes, forcing many pellet stove manufacturers to recommend their stoves be installed with outside air intake. This ensures their stoves will run efficiently, and prevents potential negative pressure within the home.
In many states pellet fuel is exempt from sales tax.
Components
A pellet stove normally consists of these components, whether basic or complex:
1. A hopper 2. An auger system 3. Two blower fans (combustion and convection) 4. A firebox (burn-pot and ash collection system), sometimes lined with ceramic fiber panels 5. Various safety features (vacuum switch, heat sensors) 6. 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.
