How Do Pellet Appliances Work?
Pellet appliances are similar to wood burning appliances only in that they burn solid fuel to create heat. EPA clean burning wood appliances are air tight appliances, meaning that you load all the fuel for a fire into the firebox at once, close the door, and control the combustion process by controlling the air flow. The more air you allow into the firebox, the faster the fuel burns. Pellet appliances are the opposite. Air is blown through the firepot chamber while the fuel is slowly metered into the combustion zone. The feed rate is increased to increase heat output and reduced to produce less heat. Pellet combustion is a much more controlled system.
General Operation
Pellet appliances have a fuel storage hopper, usually behind the combustion and heat transfer area, that normally holds about a bag of fuel or more. Large hoppers are great, but most consumers go through about a bag of fuel a day, depending on the size of their home and heating needs. During the coldest months, it might be two bags a day, but it's easy to load one bag in the morning and one in the evening. Usually, a bag-size hopper is sufficient.
The fuel is fed from the hopper into the firepot by an augur system. It may be a top feed system where the fuel is dropped into the firepot from the top, or a bottom feed system that pushes the fuel up into the firepot from the bottom or rear of the firepot. With both systems, the rate of the feed motor controls the rate of combustion and therefore, the heat output.
A combustion blower is usually used to draw air through the combustion chamber and push the exhaust through the flue and out of the house. The combustion blower starts up to help light the fire, speeds up or slows down depending on the fuel feed rate, and then shuts off after the fire is extinguished and the firepot cools off.
An igniter is used to light the pellet fire in most pellet appliances built today. You may need to push a "start" button to begin the ignition process, or your appliance might be controlled by a thermostat. Once the fire is established, the igniter usually shuts off.
A convection blower is used to circulate air through the heat exchanger of the pellet appliance and out into the room. After the pellet appliance lights and the firebox heats up, a temperature sensor usually determines when the convection blower starts. There may be consumer control for the speed of the blower or the speed may be controlled by the temperature of the appliance. After the appliance shuts down, the convection blower usually runs until the firebox cools off. If you have a boiler, a circulation system is used to pump hot liquid through the heat exchanger and eventually throughout the home. A convection blower is not used on a boiler. A pellet furnace has a very large convection blower used to circulate warm air through your homes air duct system.
Advantages of Pellet Heat
The process listed above may sound complicated, but it makes for a very simple heating solution for homeowners. To summarize, when you need heat the most you may have to do is fill your pellet appliance and press a start button. If you have a thermostat, you won't even need to press a button. The appliance takes care of the rest. Because the fuel is very consistent, the lighting process is usually very quick, the fire burns very hot and clean, and the temperature is steady and consistent
Where do wood pellets come from?