How to avoid overfiring your wood burner

Overfiring your wood-burning stove can lead to potentially disastrous problems. It is vital to burn responsibly and not exceed your stove’s maximum temperature – prolonged and repeated overfiring can lead to increased deterioration and even permanent damage to your stove.

Any surface of your installation appearing red-hot is reason for alarm – for this to occur, the temperature will have been excessively high for a significant length of time and will need to be reduced. Cooling an overfiring stove requires caution and patience – keep reading to learn how to identify overfiring and how to stop it from happening to you.

What is overfiring?

Also known as a runaway burn, overfiring is simply your fire burning too hot for your stove. Every stove is designed to unique specifications and has a maximum temperature that it is capable of withstanding. A number of issues arise when your stove’s fire gets out of control and produces excessive amounts of heat. It is unlikely that your warranty will cover damages resulting from prolonged overfiring.

What causes a stove to overfire?

Overfiring is caused by an excess of oxygen or fuel. Oxygen, fuel, and heat are the three components of a fire – increasing one of these will increase the intensity of a fire. When your stove has too much wood or an excessive amount of airflow, it can cause it to overfire as these factors increase the amount of fuel and oxygen, respectively.

Overloading your stove with wood provides an excess of fuel, creating a runaway burn that becomes uncontrollably hot whilst also potentially blocking the tertiary air vents and preventing the secondary burn of gases.

Too much airflow feeds your fire too much oxygen, causing it to burn excessively. Excessive airflow can result from leaving the stove door open, improper air vent usage, or deteriorated rope seals.

Your stove’s manufacturer’s instructions will contain further information on its maximum load and optimum air control usage.

Signs of overfiring

During operation, you can identify signs of overfiring by looking out for:

• Blackened stove glass
• Unusually high temperatures in the room
• Red-hot sections of your stove or flue pipe
• Whooshing or blowing sounds

On a cooled stove, overfiring is evidenced by:

• Disfiguration or warping to your baffle
• Damage to your stove’s exterior (cast iron stoves tend to crack or expand whereas steel bodies tend to warp or bend)
• Cracks to firebricks or mortar

Recognising when your fire is burning too hot is often quite easily apparent, either visually or by the uncomfortable amount of heat in the room. If you can identify when and how you have accidentally caused your stove to overfire, you can prevent it from happening again.

What happens if you burn too hot?

Burning for prolonged periods of time at temperatures not suitable for your appliance leads to safety concerns and will damage components of your stove.

Firewood is consumed much more quickly when burning excessively hot. This wastes fuel and creates the need to refuel much more often.

Your room will become uncomfortably hot as the fire rages and emits too much heat. This is often due to your stove’s heat output not matching the size and insulation of your room, leading to the temptation of burning at too low a temperature, causing incomplete combustion.

The exterior of your stove will reach high temperatures, posing risks to nearby furnishings and potentially resulting in the material warping, cracking, or bending.

Airwash systems can become damaged when overfiring, affecting your appliance’s stove glass and causing repeated blackening.

Consumable deterioration will occur at a significantly increased rate when your stove is consistently overfired, causing your:

• firebricks to suffer larger, more frequent cracks;
• baffle to bend and warp at a faster rate; and
• fire cement to weaken and crack more regularly.

Chimney fire risk heightens due to the temperature of  the gases in your flue increasing, causing any residual debris – such as soot or creosote – to have a higher likelihood of igniting and causing a chimney fire.

How to avoid overfiring

A key part of owning a stove is learning and understanding its operation; the more you use your stove the more confident you will get with its use. Every installation is different and subject to a multitude of variables that can affect your fire, from weather conditions to air control use. To avoid overfiring your wood burner, follow these tips:

1. Use a stove that is suitable size for your home where its heat output is sufficient to warm the room. Visiting your local HETAS Approved Retailer and discussing your needs will ensure you get the appropriate size stove to suit you.
2. Operating your appliance according to the manufacturer’s instructions will greatly help you maintain a safe, clean, and efficient burn.
3. Only refuel your stove when it is necessary: when your fire is reduced to glowing embers.
4. Regularly get your stove serviced by a HETAS Approved Servicing Technician. They will identify and rectify any faults that may be present in your installation and causing your appliance to overfire or underperform.
5. Use an appropriate amount of Ready to Burn firewood to ensure you are getting an optimal, clean, and efficient burn – rather than overloading your stove with wet, unseasoned wood.
6. Regularly maintaining your stove and getting your chimney swept by a HETAS Approved Chimney Sweep will keep your installation functioning efficiently and safely, preventing issues that cause overfiring.

How to cool down an overfiring stove

An overfiring stove is dangerous and it is important that you are cautious when interacting with it. There are some inadvisable ways to cool down an overfiring stove that can result in additional hazards, so it is important to understand how to approach the situation.

Cooling down your wood burner

To cool down an overfiring stove, you will need to reduce the airflow by partially closing the air vents, reducing the oxygen intake. This will slowly lower the temperature as your fire’s oxygen supply depletes, calming the fire and bringing your stove down to a more appropriate temperature. Patience is key – this will take some time and will require monitoring to ensure your fire does not deplete so much that incomplete combustion occurs. Once your fire has returned to the optimal temperature, be sure to remember to adjust your air control vents accordingly.

What not to do

If your stove is overfiring, it is key that you safely reduce the temperature without producing additional hazards. When trying to cool down an overfiring stove, do not:

• Throw water on the fire
• Open the stove door
• Touch your stove
• Fully close the air vents (this is not possible in most modern stoves)

Prevention is better than cure

As with most things, preventing the issue is much better than having to deal with the consequences it brings. Always burn responsibly, follow the manufacturer’s instructions, and keep your installation well maintained to prevent the risk of a runaway burn occurring.

Is it possible to not burn hot enough?

Just as you can burn too hot in your stove, you can equally not burn hot enough. If your fire is too low a temperature, it is likely that incomplete combustion will occur, causing a number of issues such as reduced heat and increased emissions.

It is important to use a stove with a heat output that matches your room. If your stove is too large for your room, it may be tempting to run it at a sub-optimal temperature by turning the controls down so that you can stay comfortable – this is called ‘slumbering’. Slumbering your stove can be extremely dangerous and should be avoided unless your appliance is specifically designed to do so.

Speak to your HETAS Approved Retailer to make sure you select the right size stove for your home.

If you are ever worried or unsure about something related to your wood-burning stove, contact your HETAS Approved Servicing Technician to visit and investigate. They have the experience, expertise, and skills to identify and rectify any faults, keeping you burning safely.