How A Wood Burning Stove Works (With Diagrams)

In Indoor Fireplaces, Wood Burning Stoves by James O'KellyLeave a Comment

Wood burning stoves work by creating a controlled environment in which wood can be burnt more efficiently to produce heat.

Wood stoves don’t have any electrical components or moving parts, but require manual input from the user to be able to operate effectively.

A wood burning stove works by:

  • Allowing a fire to burn wood inside an enclosed compartment surrounded by fireproof materials.
  • The size of the firebox dictates how much wood can be added to the fire and influences how much heat can be generated.
  • The airflow to the fire can be controlled using the air vents on the stove to be able to burn the wood more slowly and efficiently.
  • Waste gases produced by the fire are held inside the stove for longer and at higher temperature to produce more heat through secondary combustion.
  • Heat is radiated out into the room thanks to metal bodies on the stove.

I’ve explained how a wood burning stove works in more detail below using our own wood burning stove as an example.

This guide shows how wood burning stoves work. To see how multi fuel stoves work, which can burn types of fuel other than wood, click here.

How A Wood Burning Stove Works

The main issue with open fires in traditional fireplaces is that much of the heat produced is lost up the chimney, because the amount of air getting to the fire can’t be managed and so the fire can’t be controlled effectively.

Open fireplaces are therefore very inefficient at providing heat to a room, and we find that we always have to sit near our open fireplace just to feel the heat.

Wood burning stoves help to solve this problem of inefficient heating by allowing you to control both the amount of wood and the supply of air to the fire.

Burning Wood More Efficiently

Wood burning stoves help to provide more heat to your room by burning the wood more efficiently.

A wood stove helps to provide the most amount of heat possible from burning wood through two key ways:

  • Burning the wood in a more controlled manner.
  • Burning off excess gases from the fire to produce even more heat.

In a wood burning stove, a fire is built and lit inside the firebox. The inside of the firebox is lined with fireproof material on the base, sides and back.

Where the fire is built inside a wood burning stove

The door is located on the front of the stove, and has a glass panel built in to allow you to view the fire.

Stove Glass Clean
The door to our wood burning stove is largely a glass panel

A seal around the door means that when the door is closed, all of the air being supplied to the fire is through the air vents.

Depending on the model of stove and its design, wood burning stoves typically have one or two air vents. Our wood burning stove has one controllable air vent that’s located underneath, and can be opened or closed using the handle that sticks out the front.

The main air vent located under our wood stove
Wood Stove Vent
The handle to control the airflow into the stove

Wood burns best with a source of air from above, and so the diagram below shows how the fire in a wood burning stove is typically supplied with air.

How Wood Burning Stove Works
How airflow in our wood burning stove stove works

Along with how much wood is put on the fire, the main way to control how hot and fast a fire burns inside a wood stove is by using the air vents.

Opening the vent(s) increases the flow of air to the fire, causing the fire to burn through the wood more quickly because it has a greater supply of oxygen. More heat is produced as a result.

Closing down the air vent(s) reduces the oxygen supply to the fire, causing it to burn through the wood more slowly, which in turn produces less heat. Completely closing the vents prevents any air from getting to the fire and causing it to eventually go out.

As wood burning stoves are designed to be more efficient than open fireplaces, the air supply to the fire needs to be controlled so that the fire is burning through the wood at a steady pace. A fire that is smoldering due to lack of air, or rapidly burning through the wood due to a large air supply, is very inefficient.

Secondary Burn

As well as helping to burn wood in a more efficient manner, a wood burning stove also typically burns waste gases from the fire to produce even more heat through a process known as secondary burn or secondary combustion.

Higher temperatures and pressures are required to burn off waste gases from a fire, and so a wood burning stove achieves this by providing an enclosed environment whereby the air can only enter the stove through the air vents and leave the stove via the flue.

Wood burning stoves are designed to stop waste gases from leaving the firebox too quickly, so that more time is allowed for secondary combustion to occur.

A baffle plate located at the top of the firebox helps to stop the air, and forces it through a small gap at the top of the stove before leaving your home.

The top of the firebox inside our wood stove showing the baffle
Waste smoke and gases leave via the flue at the top of the wood stove

Wood burning stoves also provide a fresh supply of air to above the fire so that secondary combustion can occur. While primary air is typically supplied to the fire to burn the wood, either secondary air or tertiary air is supplied to above the fire to be used in secondary burn.

I’ve explained primary, secondary and tertiary air in stoves here.

Our wood stove has a set of tertiary air vents located at the back of the stove that provides a fresh supply of oxygen for secondary burn.

Wood Stove Tertiary Air Vents
Tertiary air vents inside our wood stove to aid in secondary combustion of waste gases

The diagram below shows how air is supplied to the fire to aid in secondary combustion of waste gases on our particular model of wood burning stove.

How Secondary Combustion Works Wood Stove
How tertiary air enters our wood stove above the fire to aid in secondary burn

Combined with burning the wood more slowly and efficiently, secondary burn helps wood burning stoves to produce the most amount of heat possible from each piece of wood burnt.

Each model of wood stove is designed differently and so how well a stove converts wood into heat will be slightly different. Our wood burning stove has an efficiency rating of 78.9%, but you can find wood stoves with efficiency ratings of 80%+.

This is compared to open fireplaces where the efficiency of burning wood can be as low as 10 or 20%, meaning that a large proportion of the heat produced isn’t used to heat your home.

Radiating The Heat

The body of a wood burning stove provides the means of transferring the heat produced from the fire to your room.

Our wood stove is made from steel, and helps conduct the heat generated by the fire and radiates it out into the room.

The main body of our wood burning stove that radiates heat into the room

Keeping The Glass Clear

As wood burning stoves help to contain a fire within a metal and glass body, the glass on the door of the stove can blacken over time through use.

Byproducts such as creosote created from burning wood can line the inside of the glass and leave stains. This can build up over time and prevent you from fully enjoying the view of a fire.

Here’s what the glass on our wood burning stove can sometimes look like after a number of fires.

Without air wash the glass door can blacken over time

To help overcome this problem, many wood burning stoves incorporate what’s known as an air wash system. A constant flow of air is supplied down the inside of the glass to help prevent deposits from settling on the glass.

How Air Wash Works Wood Stove
How secondary air is supplied to the glass to help keep it clean in our wood stove

Our wood burning stove has air wash built in, and secondary air from the vent located underneath the stoves provides the air needed for the air wash.

With the main vent on our wood stove open, the air wash system helps to keep the glass clear throughout each fire.

Air wash allows us enjoy the view of the fire by helping to keep the glass clean

Further Reading

How To Use A Wood Burning Stove

Parts Of A Wood Burning Stove Explained

How To Build And Light A Fire In A Wood Burning Stove

Leave a Comment