Pellet stove
From Wikipedia, the free encyclopedia
A pellet stove is an appliance that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. 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 can be either free-standing units or fireplace inserts vented into an existing chimney. The pellet stove has changed in appearance over the years from a simple, boxy workhorse design, to a decorative heating appliance. However, most all pellet stoves are constructed using large, conductive, cast-iron pieces, with stainless steel to encase circuitry and exhaust areas.
The heating industry has considerably shifted toward biomass stoves and heating devices based on efficient combustible and renewable resources. This was a trend that began during the 1973 oil crisis causing the creation of the first pellet stoves. Even so, pellet stoves have become a viable, economical, and popular option for home heating systems only in the last ten years. Many pellet stove manufacturers recommend the use of a corn and pellet mixture, though some are UL listed for fuels other than pellets, such as wheat, sunflower seeds, and cherry pits.
Contents |
[edit] 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 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.
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 do not usually require a vertical rise to vent, although a three to five foot vertical run 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.
In many states in the U.S., pellet stoves and fuel are exempt from sales tax.
[edit] Principles of operation
A pellet stove normally consists of these components, whether basic or complex.
- A hopper
- An auger system
- Three blower fans (combustion, convection, and exhaust)
- A firebox (with refractory panels, burn-pot, and ash collection system)
- A vacuum pump
- A main control box/board (or "brain")
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 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 as a combustion blower introduces air into the bottom of the burn-pot. While some pellet stoves will be hot to the touch (especially on the viewing window), most manufacturers utilize a series of cast-iron 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 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 enabling the controller to shutdown if any safe conditions are exceeded.
Pellet stoves can either be lit manually or through an automatic ignitor. The ignitor 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.
[edit] Pellet stove maintenance
 |
This section may be unencyclopedic. Please help improve this article by removing or rewriting this how-to section, which may qualify to be imported to Wikibooks. (talk) |
A pellet stove, to prevent incomplete combustion and electrical failure, will need to be cleaned on a regular basis. Normal, frequent cleaning of the main components can increase both the life and the efficiency of the stove. During a heating season, superficial cleaning should be performed once every 2-5 days, depending on ash build-up. Most all pellet manufacturers recommend that after three full tons have been burned (or after a heating season), a pellet stove and all venting should be completely cleaned and inspected. This can be performed by a certified professional in your area, or in most cases by the owner of the stove (although a periodic inspection by a professional may be required to continue a manufacturer's warranty and is highly encouraged).
A normal, frequent cleaning requires a relatively superficial method and can be performed by most anyone. Always allow the unit time to shut-down and cool before servicing. Using a scraping tool such as a steel wire brush or a paint-stripper, clean out the burn-pot and make sure all air-holes are free of debris. With a paint-brush or vacuum hose, wipe away any fly-ash in the firebox along the sides and top. Also, most pellet stoves will have an ash pan that may or may not need to be emptied during each cleaning. And If the stove includes tube-shaped heat exchangers, in most cases a small scraper will exist attached to the top of the burn-pot; pull this to the full extent once or twice. To clean a stove's glass front, simply use a wet cloth or in more extreme cases, a vinegar based window cleanser.
A more in-depth, yearly cleaning requires disassembly of the unit to inspect and clean the inner workings. Also included in a yearly cleaning should be the sweeping of all venting, both inside and outside of the stove frame. With a three or four inch brush (depending on your venting size), attached to a flexible rod, sweep the inside of the pellet piping, making sure to dislodge as much fly-ash as possible. Seal any joints that must be taken apart after satisfactorily cleaning the outside venting. Within the back of the stove, check to see that all fan systems are running smoothly, and wipe down any filters that may be clogged with dust (this may require dislodging all side and back panels that form the body of the unit). If there is any gasket material that is damaged (a rope-like material lining certain openings), remove and replace it with new gasket. Inside the firebox, there will be passageways for both combustion and exhaust air that need to be addressed. These are usually located behind a faux brick refractory or panel that can become unattached in some fashion. Clean these ports with a steel brush or a vacuum, trying to remove all debris. Take care when replacing refractory pieces, as any restriction to airflow may cause excessive ash build-up. Again, check the firebox for any damaged gasket material, remove and replace it with new gasket.
[edit] Recent Shortage
There is a recent shortage of pellets due to factory closings and increased demand in the United States, causing most prices to double during the 2006-2007 winter. In most areas, especially in the northeast, prices have almost tripled from an average of $167 per ton to well over $400.
