Pellet stove

Pellet stove

Overview
A pellet stove is a stove
Stove
A stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it...

 that burns compressed wood or biomass pellets
Wood pellets
Wood pellets are a type of wood fuel, generally made from compacted sawdust or other wastes from sawmilling and other wood products manufacture, but also sometimes from sources such as whole-tree removal or tree tops and branches leftover after logging and which otherwise help replenish soil...

 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.

Scrap wood and ship-lap burners have been around for decades. Barrel stoves, braziers, and oil drum fires in Depression-era Hoovervilles
support this.
Discussion
Ask a question about 'Pellet stove'
Start a new discussion about 'Pellet stove'
Answer questions from other users
Full Discussion Forum
 
Unanswered Questions
Encyclopedia
A pellet stove is a stove
Stove
A stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it...

 that burns compressed wood or biomass pellets
Wood pellets
Wood pellets are a type of wood fuel, generally made from compacted sawdust or other wastes from sawmilling and other wood products manufacture, but also sometimes from sources such as whole-tree removal or tree tops and branches leftover after logging and which otherwise help replenish soil...

 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.

Background and history


Scrap wood and ship-lap burners have been around for decades. Barrel stoves, braziers, and oil drum fires in Depression-era Hoovervilles
support this. Professionally built wood ovens
Wood-fired oven
Wood-fired ovens, also known as wood ovens , are ovens that use wood fuel for cooking. There are two types of wood-fired ovens: "black ovens" and "white ovens"...

 with sawdust hoppers were used in the early part of the century. All of these units used scrap and loose wood, or sawdust. In 1930, the Presto-Log was invented reusing scrap sawdust from the Potlatch pine mill in Lewiston
Lewiston
Lewiston is the name of some places in the United States of America:*Lewiston, Alabama*Lewiston, California*Lewiston, Georgia*Lewiston, Idaho*Lewiston, Illinois*Lewiston, Maine*Lewiston, Michigan*Lewiston, Minnesota*Lewiston, Nebraska...

, Idaho, as domestic heat. From this came the miniaturized pellet stove, which emerged from Washington State in the 1980s.

The pellet stove has changed in appearance over the years from a simple, boxy workhorse design, to a decorative heating appliance. Pellet stoves can be either free-standing units or fireplace inserts vented into an existing chimney. Most pellet stoves are constructed using large, conductive, steel or cast-iron pieces, with stainless steel to encase circuitry and exhaust areas.

Pellet furnaces and pellet boilers are also available in addition to the decorative stove. These units can be retrofitted into existing home heating systems with only minor changes to existing ductwork and or plumbing.

The heating industry has considerably shifted toward biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 stoves and heating devices based on efficient combustible and renewable resources. This was a trend that began during the 1973 oil crisis
1973 oil crisis
The 1973 oil crisis started in October 1973, when the members of Organization of Arab Petroleum Exporting Countries or the OAPEC proclaimed an oil embargo. This was "in response to the U.S. decision to re-supply the Israeli military" during the Yom Kippur war. It lasted until March 1974. With the...

 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
Underwriters Laboratories
Underwriters Laboratories Inc. is an independent product safety certification organization. Established in 1894, the company has its headquarters in Northbrook, Illinois. UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing...

 for fuels other than pellets, such as wheat, corn, sunflower seeds, and cherry pits.

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
Creosote
Creosote is the portion of chemical products obtained by the distillation of a tar that remains heavier than water, notably useful for its anti-septic and preservative properties...

, 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
Woodchips
Woodchips are a medium-sized solid material made by cutting, or chipping, larger pieces of wood. Woodchips may be used as a biomass solid fuel. They may also be used as an organic mulch in gardening, landscaping, restoration ecology and mushroom cultivation...

. 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
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...

 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 ensure their stoves will run efficiently, and prevents potential negative pressure within the home.

In many states pellet fuel is exempt from sales tax.

Tax Credit


In most states in the US
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, a 75% efficient pellet stove is eligible for a tax credit up to 30% of the cost of the appliance, plus labor.

Principles of operation



A pellet stove normally consists of these components, whether basic or complex:
  • A hopper
  • An auger
    Auger
    An auger is a drilling device, or drill bit, that usually includes a rotating helical screw blade called a "flighting" to act as a screw conveyor to remove the drilled out material...

     system
  • Two blower fans (combustion
    Combustion
    Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

     and convection
    Convection
    Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

    )
  • 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.

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.

Corn stove



A corn stove is designed for whole kernel shelled corn combustion and is similar to a pellet stove. The chief difference between a pellet stove and a dedicated corn stove is the addition of metal stirring rod within the burnpot or an active ash removal system. These vary in design slightly, but usually consist of one long metal stalk with smaller rods welded at a perpendicular angle, in order to churn the burn-pot as it spins. An active ash removal system consists of augers at the bottom of the burn pot that evacuate the ash and clinkers. During a normal burn cycle, the sugar content within corn (and other similar bio-fuels) will cause the ashes to stick together, forming a hard mass. The metal stirring rod, which is usually connected to a motor by a simple chain system, will break apart these masses, causing a much more consistent burn. While there is a push to create stoves that are able to burn multiple fuels with minimal adjustments, some pellet stoves are not designed to stir fuel and will not burn corn.

See also

  • Corn kernels
    Corn kernels
    Corn kernels are the seeds of maize.Corn kernels are used as pelletized fuel for pellet stoves and furnaces. Corn kernels are a natural pellet, which gives them a huge economic advantage over other man-made biomass pellets and wood pellets....

  • Renewable heat
    Renewable heat
    Renewable heat is an application of renewable energy and it refers to the renewable generation of heat, rather than electrical power ....

  • Pellet Fuels Institute
    Pellet Fuels Institute
    Pellet Fuels Institute is a U.S. trade organization that represents manufacturers, retailers and distributors of wood pellet fuel supplies and appliances....

  • Wood pellets
    Wood pellets
    Wood pellets are a type of wood fuel, generally made from compacted sawdust or other wastes from sawmilling and other wood products manufacture, but also sometimes from sources such as whole-tree removal or tree tops and branches leftover after logging and which otherwise help replenish soil...