What Is Over Firing A Wood Stove?

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

Over firing a wood burning stove can cause long-term or permanent damage to the main components inside a stove.

Manufacturers of wood burning stoves recommended to only have a certain amount of wood in the stove at one time. Placing too much wood into a stove or allowing too much air flow to the fire can cause the stove to over fire.

So what is meant by over firing a wood stove?

Over firing a wood stove is when more fuel or oxygen has been provided to the stove over and above what has been designed, and the extra heat created by the additional fuel or oxygen can cause damage to the stove.

Wood burning stoves are designed to only operate at a certain temperatures, and over firing a stove can cause temperatures to be hotter than the materials within the stove can take.

I’ve discussed below how you can prevent overloading your wood burning stove, what happens if a wood stove gets too hot, and how you can cool down a stove that is too hot.

What Is Over Firing A Wood Burning Stove?

Over firing a wood stove is when a fire is burning bigger, hotter and faster than required for the stove to provide it’s normal operating heat output.

Every model of wood burning stove has been designed differently, and these differences can be how much wood the firebox is able to hold, how efficiently oxygen can get to the fire, and how well the stove converts energy stored in the wood into heat.

In general, the larger the stove the more heat it can give out, because it can hold and burn more wood at any one time. Oxygen, efficiency of the stove and secondary burn, among other factors can also influence the total heat output.

Manufacturers state how much wood should be in the firebox at any one time, and each stove has been designed to burn a specific amount of wood. The maximum permitted heat output of a stove will be within safety limits designed to help prevent damage or harm caused to the user or the building.

Placing more fuel in a stove fire than recommended can cause the stove to heat up to temperatures beyond what the stove hasn been designed to cope with.

Over firing a wood burning stove that leads to unsafe temperatures can also in turn create unsafe temperatures inside the flue or chimney. Burning wood releases smoke, soot and creosote; the latter of which can line the inside of a flue over time.

Creosote is a highly combustible material, and the potential for a chimney fire to occur can increase as the temperature of a wood burning stove increases. The extra heat generated by an over firing stove can cause hot air to ignite the creosote.

Having your chimney or flue swept at least once per year in line with recommend guidelines helps to reduce the chance of chimney fires.

Along with overloading of fuel, allowing too much air into the stove can cause also over firing. An excess of oxygen can cause the fire to grow out of control, and so it’s important to understand what the purpose is for each air vent on a stove and how they should be used to control the fire (Read more about the different air vents on a wood stove here).

Leaving the stove door open, or the air vents wide open, will fuel the fire with large amounts of oxygen.

Can You Overload A Wood Stove?

If you put more wood into a wood burning stove that what is recommended you can overload the stove, and potentially cause the stove to over fire.

Overloading a stove may also cause issues with the air wash or secondary burn systems.

If you aren’t familiar with air wash on a wood stove you can read more here, and for more information on secondary combustion in stoves click here.

For our wood burning stoves, the manufacturer’s instruction manuals state not to over fire the stoves, and have recommended maximum amounts of wood to be inside the firebox at any one time.

Here’s one of our wood stoves:

Wood Burning Stove

The stove has a set of tertiary air vents at the back of the fireplace that aid in secondary combustion.

Tertiary Air Vents
Tertiary air vents inside a wood stove

The stove’s manual states that wood can be stacked up inside the stove, but no higher than these tertiary air vents. If we were to overload this stove with too many logs then it may cause the stove to over fire, as well as preventing the secondary burn of gases from occurring if the tertiary air vents are blocked. 

Hunter Stoves, the manufacturer of this stove, state in the instruction manual that:

‘It is possible to fire the stove beyond its design capacity. This could damage the stove so watch for signs of overfiring. If any part of the stove starts to glow red, the stove is in an over-fire situation and the controls should be adjusted accordingly.

The maximum amount of fuel specified in this manual should not be exceeded, overloading can cause excess smoke.’

Hunter Stoves

Therefore, in order to prevent overloading of your wood burning stove, which in turn can cause over firing, ensure to read your stove’s instruction manual for recommendations on maximum amounts of wood to be in the firebox at any one time.

What Happens If A Wood Stove Gets Too Hot?

A wood burning stove that is too hot can cause metal components to become permanently damaged through warping, weakening or cracking.

Regularly over firing your wood burning stove can cause any problems to the metal components to occur more quickly. Wood burning stove made of steel are more likely to bend and warp, while cast iron stoves can begin to crack or even expand due to prolonged high temperatures.

The baffle plate located inside the top area of a wood stove can be at most risk of damage due to an over firing stove because it’s located right above the fire. The baffle helps to hold gases in the firebox for longer before exiting through the flue, and to also reflect heat back into the firebox.

Here’s a picture of the baffle in one of our wood burning stoves:

Baffle Plate
The baffle inside one of our wood stoves. In used condition but no clear issues as a result of too high temperatures

The baffle has seen a lot of heat, but it’s still structurally sound. There’s no sign of warping or any other heat damage. A common sign of a baffle that has been subject to higher temperatures due to over firing is sagging of the plate, or discoloration.

If a wood stove gets too hot it can also cause damage to the base of the firebox.

One of our wood stoves has a metal grate at the base of the firebox, and so we ensure to keep a bed of ash to help protect the grate from the fire. More on how much ash to leave in a wood burning stove here.

Firebox Grate
Metal firebox grate that can be at risk of damage from over firing

If at any point a metal part of a wood stove start to glow red, then that component may start to be at risk of damage from being too hot. Another sign that a stove is getting too hot and over firing is the sound of more oxygen being sucked into the stove than usual.

We might not always be able to see or tell whether inside parts of the stove are at risk of being damaged during a fire, and so we have a thermometer that we’ve stuck on the outside of one of our stoves to give us an indication of whether temperatures inside the stove are getting too high.

Wood Stove Thermometer
The thermometer we use to check how hot the wood stove is getting

You can use the thermometer in conjunction with the stove’s recommended operating temperatures (typically found in the instruction manual) to check whether the stove is operating above designed temperatures.

You can also use a stove pipe thermometer to measure the temperature of the air leaving the stove through the flue.

How To Cool Down A Wood Stove That Is Too Hot

To help cool down a wood burning stove that has over fired and temperatures are too high, try a combination of the below:

  • Close down the air vents as much as possible to reduce the oxygen supply and settle the fire, without starving the fire with oxygen and causing it to go out. On EPA or DEFRA approved stove you typically won’t be able to fully close a vent as it can cause the fire to smoke. (More on DEFRA approved stoves here).
  • Push the logs further together and into the ashes/embers to help reduce the airflow around them.
  • If you have a damper, close it down as much as possible without putting the fire out. Don’t completely close down the damper as this can cause smoke and gases to enter your home (For more information i’ve put together the complete guide on fireplace and stove dampers right here).
  • Turn the stove blower on full (if it has one).
  • Leave any doors to the room wide open.
  • Open the stove door to provide a rush of cooler air.

See exactly what’s inside our wood burning stoves with photos of the firebox, baffles, flues, air vents and more.

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