How does a pellet stove work? A wood pellet stove burns compressed wood pellets which are fed from the pellet hopper into the combustion pot by an auger.
The fire is fed fresh air rich in oxygen by a combustion fan. Heat is transferred through a heat exchanger before combustion gases are vented. The transferred heat heats air being pulled into the stove and blown into the room by the distribution fan. Ashes fall into the ash pan which can be emptied when full.
That’s the quick answer of how a wood pellet stove works.
- How a Wood Pellet Stove Works – Step by Step
How a Wood Pellet Stove Works – Step by Step
Here are more details. Please refer to the diagram and numbers for a fuller understanding of which part of the wood pellet stove is discussed in each step.
Step 1: Filling the Hopper & Increasing Capacity
The hopper is filled with wood pellets. Most stoves have the hopper on top, but it is on the side or near the bottom on some stoves.
To go longer between filling the hopper, a hopper extension can be added and filled with pellets. This can increase capacity by two to three times.
Most pellet stoves need to be refilled with pellets every 1 to 4 days depending on the size of the hopper, whether an extension is in place and how much the stove runs.
Step 2: Feeding Pellets to the Fire Pot
The auger has a spiral design, and pellets are carried upward as it turns. When the pellets reach the shoot, they fall into the flames.
The auger is turned by a small motor, which is controlled by a thermostat. The auger and motor together are called the auger system or auger assembly. The parts can be replaced together or independently.
When the thermostat calls for heat, the auger motor begins. The auger pulls pellets from the hopper and feeds them into the combustion or burn pot, which is often lined with fire bricks (preferred) or a double-thick steel liner or similar. This pot is also called the combustion pot or combustion chamber.
Step 3: Igniting and Burning Wood Pellets
The burn pot is where the action happens. Pellets in the pot are ignited in one of two ways.
More affordable stoves are lighted manually. A gel accelerant or other safe type can be used when starting the stove “cold.” A long butane lighter, like a barbecue lighter like these, is the best tool to light the pellets and avoid getting burned.
If you spend a little more, your stove will have electronic ignition. The most common a glow plug or hot surface igniter. They are much heavier duty than those in gas furnaces. An electric current is sent to the igniter, and resistance heat causes it to get hot enough to start the pellets on fire.
Do you enjoy the ambience of a fire? Then choose a wood stove with a heat-proof glass window for watching the flames!
We won’t list a separate step for this, but see how the burned pellet turns to ash and falls into the ash pan through a grate? Some burn pots hold the ash until a lever is moved that opens the bottom of the pot and allows the ashes to fall.
Most ash pans can be conveniently accessed and removed for emptying.
Did you know? There are many good uses for wood ashes including deterring pests, boosting your garden’s performance, using as a safe alternative to chemical-based cleaners and reducing slip possibilities on icy sidewalks without using harsh salt or chemicals!
Step 4: Feed Fresh Air to the Fire!
Wood pellets will smolder and smoke without being fed fresh air.
Some cheap wood pellet stoves have only a vent for getting fresh combustion air.
But most are fed air with a small combustion motor as shown in the diagram. If you have a gas furnace, it’s like the draft inducer motor, but it runs continuously to enhance the purity and heat of the burn. The motor is located in a tube that pulls in air from around the stove and blows it directly into the burn pot.
Step 5: Transfer Heat from Combustion Gases
Like most heating appliances, wood stoves are fitted with one or more heat exchangers. They are formed from one or more tubes with enhanced surface area for great heat transfer.
The combustion gases created in the burn pot pass through the heat exchanger on their way to the vent.
Step 6: Blow Heated Air Into your Living Space
As the gases pass through the heat exchanger(s), heat transfers through the metal into a chamber containing the convection blower. Some fans start the blower when the thermostat calls for heat, but that can blow cool air into the room until the fire gets hot. Other stoves have a flame or temperature sensor. When the heat temperature gets high enough, the sensor allows the blower to start.
The warmed air is blown into the room through a vent in the stove. Vents can be placed in any location, but the diagram shows the most common spot for the warm air vent or grate.
How efficient is a wood pellet stove? With modern heat exchangers, the best wood pellet stoves are about 80% efficient. That means 80% of the heat created is transferred and pushed into your living space. The total efficiency range is given by the US Department of Energy, in its handy Pellet Stove Guide, as 70% to 83%.
Step 7: Get Rid of Combustion Gases
The last step is to vent the exhaust.
Why can’t heated air from the burn pot be sent directly into your home? For two obvious reasons. First, it is smoky. Secondly, and most importantly, it contains deadly gases such as carbon monoxide. They must be prevented from entering the air you breathe.
The exhaust outlet is often on top of the stove, but it can be in the rear too.
What isn’t shown? The exhaust flue/chimney isn’t shown. It must be connected to the exhaust outlet to carry the poisonous gases out of your home for safe venting to the outdoors. Here are two common chimney options.
Those are the basics of how a wood pellet stove works.