Pellet stoves are relatively complex appliances and have a whole host of integrated mechanical and electronic components that work together to create the most efficient form of solid fuel combustion home heating appliance.
To help explain how pellet stoves work we’ve put together this complete guide on how a pellet stove works using our own pellet stove as an example.
A pellet stove works by:
- Using electricity to power all of the electrical and mechanical components within the stove.
- Delivering fuel from the hopper storage area within the stove to the combustion chamber using a screw auger.
- Removing waste air from the combustion chamber using a fume extractor and forcing waste air out of a home via a flue using the combustion blower.
- Creating a vacuum inside the combustion chamber which allows fresh air to be sucked into the stove to feed the fire.
- Mixing fresh air and fuel in the form of pellets within the combustion chamber to generate heat using real flames.
- Automatically controlling all of the burning processes using a central control unit that’s fed live information from a range of temperature and pressure sensors.
- Providing warm air to the room through convection of air, where a distribution blower forces cooler air over a heater exchanger located on the outside of the combustion chamber to heat the air as it passes over.
We’ll be using our own pellet stove to explain how a pellet stove works in more detail below, explaining more about how each element of a pellet stove works and how each component comes together to deliver the most efficient burn of solid fuel.
1) Powering The Stove
Pellet stoves are electrical appliances meaning they require a source of electricity in order to work.
This means that pellet stoves will comes with a power cord and plug that will need to be plugged into a nearby electrical outlet otherwise the stove won’t even turn on.
In the case of our pellet stove, the power cord came detached from the stove and so we simply needed to first plug it into the back of the stove.
The other end then needed plugging into a nearby electrical outlet.
Turning on the mains power switch at the back of the stove provides power to the stove, and for our own pellet stove the central control screen then powers up.
The only exception to this would be if using a very niche non-electric form of pellet stove, but these are far less common than their electric counterparts.
2) Storing & Delivering The Fuel
In terms of storing and delivering fuel, the manual to our particular model of pellet stove explains:
‘The pellet fuel hopper is located at the rear of the pellet stove. Filling of the hopper is made through a hatch located in the rear part of the upper top of the pellet stove. The pellets are transported from the hopper to the combustion chamber by means of a screw auger driven by a gear motor.’
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Unlike other forms of wood stove that require the fuel to be manually added to the fire, pellet stoves store the fuel within the stove and automatically deliver the fuel to the fire.
The fuel for a pellet stove is stored within the hopper.
The hopper on our particular pellet stove is located at the top of the unit and we need to add the fuel into this hopper before the stove can work.
Fuel for a pellet stove comes in the form of pellets, which is material such as wood by-products compressed into a small area as a pellet shape.
With the pellets stored within the hopper, a pellet stove needs to deliver them to the fire in the combustion chamber in order to be burnt to produce heat.
A pellet stove therefore uses a motorized screw auger to release the pellets from the hopper down a chute to the fire.
The auger will be located within the hopper of a pellet stove. It will be pick up pellets from the bottom of the hopper and move them up to the top of the auger as it rotates.
Once pellets reach the top of the auger they fall down a chute to the combustion area where the fire will be located. The outlet to this chute can be seen in our pellet stove below, and the top of the auger can be seen when looking up the chute.
The auger will be connected to a motor, which in the case of our pellet stove is located beneath the auger under the hopper. As the motor turns the auger rotates, and the quicker the motor turns the more pellets are delivered to the fire.
A pellet stove doesn’t just deliver pellets to the fire continuously. The motor is connected up the central control unit of the stove, which tells the auger how many pellets to deliver to the fire and how often.
3) Removing Waste Air
In order for a pellet stove fire to be fed with fresh oxygen the waste air must first be removed.
Unlike other forms of wood stove where the natural movement of air (known as the draft) is used to remove waste gases, pellet stoves use forced ventilation to remove waste air from a home.
This works thanks to a combustion blower within a fume extractor that sucks air out of the combustion chamber of a pellet stove.
The fume extractor is located beneath the combustion chamber in our particular model of pellet stove but is hidden out of view within the body of the stove.
Waste air leaves via the top of the combustion chamber in our pellet stove, bypassing a couple of baffle plates on the way. These baffle plates help to slow down the rate at which the air leaves and increases the pressure within the combustion chamber, helping the stove to generate more heat and be more efficient.
Once the waste air leaves the combustion chamber of a pellet stove and passes through the fume extractor, it leaves the stove via the flue socket.
The flue socket will in most cases be found on the back of the stove, as it is with ours.
The flue system that is used to remove the waste air out of a home is connected up to this flue socket. As a pellet stove uses forced ventilation, installing a flue for use with a pellet stove can be more flexible compared to other forms of wood stove.
For example, while our wood burning stoves vent straight up through the roof within the chimney, we’ve had the flue for our pellet stove installed horizontally through an external wall, which then heads straight up the outer wall of the house to above the eaves.
4) Supplying Fresh Air
Through the forced removal of waste air in a pellet stove a vacuum is created within the combustion chamber that in turn sucks fresh air into the stove through the air vent.
The air vent on a pellet stove will usually be found on the back of the stove (where the flue socket is located) and is where the vent can be found on our pellet stove.
The clean air reaches the combustion chamber on our pellet stove from this air vent via a plastic duct.
It’s through here that all fresh air is supplied to the fire in the combustion. This helps to ensure that the oxygen supply to the fire can be controlled for efficiency purposes.
To ensure that air supply to a pellet stove fire is fully controlled, the combustion chamber will be a fully sealed system with only one way for air to enter and exit the stove. This means that any doors to the combustion chamber will need to be airtight.
For example, the door to the combustion chamber on our pellet stove has a gasket that ensures the stove remains airtight when the door is closed during fires.
For many pellet stoves there can be a choice for how the fresh air can be vented:
- Internally by taking fresh air from inside the room
- Externally by taking fresh air from outside a home.
If a pellet stove is to take fresh air from inside a room then you may not need to do anything with the air vent that sticks out the back of the stove, but depending in building regulations or codes for your particular area of residence you may need to have an external air vent (of a certain size and capacity) installed elsewhere in the same room as the stove.
The purpose of such an air vent is to ensure that there’s always a sufficient supply of oxygen in the room, which may dip to unsafe levels if a pellet stove is taking air from indoors and there’s no way to replenish the oxygen.
However, this can be solved by venting fresh air to a pellet stove externally.
This would require extending the air vent located on the back of the stove through an external wall of a home and allow the stove to take outside air.
The air supply to a pellet stove typically comes into the combustion chamber below the fire.
For example, if we remove the burn pot (where the flames would be located) from our pellet stove we can see the air supply inlet into the combustion chamber.
5) Generating The Heat
A fire in a pellet stove that generates heat for a home will be found within the combustion chamber.
The combustion chamber in our pellet stove is located behind a glass door on the front of the stove.
The doors to this chamber is sealed with a gasket to ensure that the chamber remains airtight during fires for efficiency purposes.
As a fire needs both fuel and oxygen in order to survive, this is where:
- Fresh air from the air vent located on the back of the stove is supplied to feed oxygen the fire.
- Fuel in the form of pellets is supplied to the fire from the hopper via the auger as the solid fuel burnt to generate heat.
- Waste air is removed from the combustion chamber to allow fresh air to replace it.
The burn pot is where the flames will originate from in the combustion chamber and where the pellets fall down into and where the air is directly supplied to.
The actual combustion area in the form of a burn pot is a relatively small area compared to the size of the stove.
Pellets fall down to the flames in our pellet stove from the hopper outlet just above the burn pot.
The burn pot in our stove can be removed for cleaning purposes but it has a number of holes in to allow the fuel to mix with the air being provided from below.
It’s here in the burn pot of a pellet stove where the heat is generated.
A fire in a pellet stove can typically be started automatically rather than being manually lit thanks to the ignition system.
The ignition system is located beneath the burn pot in our pellet stove and can be seen adjacent to the air inlet.
The manual for our own pellet stove explains:
‘The initial ignition of the pellets is carried out by hot air, which is sucked in around the ignition in the combustion chamber through the fume extractor.’
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Although pellet stoves are very clean burning heating appliances, they still produce some solid waste in the form of ash.
A pellet stove will therefore have an ash tray located below the burn pot to collect the ash, and in the case of our stove is removable for easier disposal and cleaning.
6) Controlling The Burn
Automated Control
Pellet stoves are set up to automatically undertake much of the processes that would need to be undertaken manually with other forms of wood stove.
This is to help remove user error and more effectively control the fuel to air ratio for the most efficient and cleanest burn with minimal wastage and emissions.
The components that are automatically controlled in a pellet stove can include:
- The combustion blower in the fume extractor dictating how much air is leaving the stove and therefore how much oxygen is being supplied to the fire.
- The auger in the hopper controlling how much fuel is being added to the fire.
- The distribution blower forcing hot air out of the stove.
All of the automated processes in a pellet stove are control by a central control unit.
The control unit in our pellet stove is located at the top of the unit just above the hopper.
The manual for our stove explains:
‘The control unit is equipped with a system for monitoring and controlling the burning process. It ensures higher efficiency, optimizes the fuel consumption and minimizes the emissions.’
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The control unit takes information from a range of sensors across the stove to understand how the stove is operating at any one time. The sensors in our pellet stove include:
- A temperature sensor within the flue outlet measuring the temperature of the gases leaving the stove.
- A pressure sensor in the combustion chamber measuring pressure for the fire.
- A temperature sensor within the body of the stove measuring the room temperature.
The manual for our pellet stove explains:
‘With sensors for the pressure in the fire chamber and temperature sensors at the flue outlet for the temperature of the flue gasses, the system analyses the collected data from the burning and automatically controls and optimizes it.’
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A control unit therefore uses current information available from the sensors to understand how the fire in the pellet stove is burning and can control all of the main processes to ensure that the correct fuel to air ratio is provided throughout the duration of the fire for maximum efficiency and minimal emissions.
A control unit on a pellet stove will therefore:
- Adjust the rate at which pellets are fed to the fire in the combustion chamber from the hopper by rotating the auger quicker or slower depending on the current situation.
- Adjust the blower speed within the fume extractor to extract waste air quicker or slower from the combustion chamber, which in turn influences how much fresh air is being supplied to the fire.
Manual Control
While a pellet stove will control all of the processes that are required to generate heat, they often have control panels where users can input or change settings depending on their personal preference.
For example, our stove has a touch screen control integrated into the control unit.
This allows us to:
- See everything that is happening including the current room temperature and fire temperature.
- Change the desired room temperature.
- Set days of the week for the stove to operate.
- Set times on each day for the stove to come on.
- Identify any problems.
- And more.
7) Delivering The Heat
Generating the heat in a pellet stove is only one part of the of the process and the heat must be delivered to the room effectively from the stove in order for a stove to be a good home heating appliance.
Pellet stoves work differently to wood burning stove in that they don’t solely rely on using the body of the stove to absorb the heat from the fire inside and radiate that heat out into the room.
Instead, pellet stoves focus on convection of warm air through using a dedicated distribution blower to deliver heat to the room.
The manual to our own pellet stove explains:
‘Through the internally mounted air fan, the hot air is pushed into the room and multiplies the efficiency of the pellet stove.’
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A distribution blower is located in our model of pellet stove towards the bottom of the unit behind the combustion chamber and can be see when looking in through the back of the stove.
The fire in a pellet stove is contained within the sealed combustion chamber, and while it can still radiate some of the heat out through the front, much of the heat remains trapped within the stove.
A pellet stove therefore delivers warmth to a room by:
- Using a blower (known as the distribution blower) to pull in cooler air from the back of the stove and force it through a duct that travels around the combustion chamber.
- As the air travels around the combustion chamber, it warms up from the fire inside.
- A heater exchanger is used to more efficiently transfer the heat from the combustion chamber to the air and can commonly be found in the form of heatsinks.
- Warm is provided through the front of the stove, commonly through a grille-like feature.
In our particular model of pellet stove, the air from the distribution blower travels around the back and top of the combustion chamber.
The heat exchanger in this stove comes in the form of heatsinks, which line this channel and allows the heat to be more effectively transferred from the fire inside the stove through the wall of the combustion chamber and to the moving air.
When our pellet stove is on, warm air can be felt coming through the front grille of the stove.
