How Much Ash To Leave In A Wood Burning Stove (With Real Examples)

In Indoor Fireplaces, Wood Burning Stoves by James O'Kelly1 Comment

Many wood burning stove manufacturers recommend to leave a layer of ash at the bed of the stove to help improve the total heat output, and to aid in the stove’s operation of any secondary burn and air wash systems.

Too little amounts of ash can prevent the fire from reaching high temperatures and cause damage to base of the stove, and too much ash can restrict sufficient airflow to the fire.

So how much ash should you leave in a wood burning stove?

The depth of ash to leave within a wood burning stove can vary between different manufacturers and models of stove, but in general around 1 inch deep of ash should be left in the bed of a wood stove before each fire.

We have a number of wood burning stoves in the family and I give examples below of how much ash we leave in two of our wood stoves, as well as explaining how often you should be removing ash from a wood stove, and when you should be emptying the ash completely.

How Much Ash To Leave In A Wood Burning Stove

Ash is left behind after having a fire in a wood burning stove, along with any bits of charred and unburnt wood. Ash can have many uses as fertilizer in a garden but leaving a bed of ash in a wood burning stove can actually be quite beneficial.  

Ash is a mixture of organic and inorganic residue that is left after the combustion of wood, and hardwoods tend to produce more ash than softwoods. Wood ash is primarily made up of Calcium but also typically includes Potassium, Phosphorous and Magnesium. [University of Georgia]

It’s sometimes believed to be better to always clean out any ash left over after a fire before having another, but many wood burning stove manufacturers recommend that a certain depth of ash should be left within the stove between fires.

Within a manual for their freestanding wood stove range, Stovax state that:

Wood burns best on a bed of ash (approx. 25mm (1”) deep).’

Wood burns better on a layer of ash because the ash helps to insulate the warmth and also helps to reflect the heat back onto further pieces of wood. It can also take a while for firebox surrounds to heat up from cold, and so a bed of ash can help to get the fire going more quickly.

A layer of ash can also make re-lighting a fire easier and more efficient because ash is such a good insulator of heat that it can trap hot coals for many hours, even after the fire has subsided.

A bed of ash may also help with a stove’s secondary combustion of gases, or its air wash system used for helping to keep the glass on the stove door clean.

You can read more about secondary combustion in wood burning stoves here.

I’ve also explained air wash systems in wood stoves and what their purpose is in more detail here.

Too little or no ash left in a wood burning stove can cause permanent damage to the base of the firebox, as metal firebox bases can become warped over time while other types of materials can begin to crack.

In comparison, too much ash can block the airflow from vents around the base of the firebox. Furthermore, as the amount of ash left in a wood stove increases, the space available for firewood decreases.

How Often To Remove Ash From A Wood Stove?

Wood burns better on a layer of ash and manufacturers recommend to keep a bed of ash to help protect the stove, but how often should you be removing ash from a wood stove?

The depth of ash should be kept fairly consistent throughout the burning season by periodically removing the required amount of ash, rather than letting the ash build up over time.

If you use your wood burning stove regularly then you’ll probably find that you’re needing to remove the ashes more frequently. Burning hardwoods can also increase the rate in which ash builds up in the stove, but it can be ok to leave up to 2 inches of ash before reducing the depth back to around 1 inch.

When To Empty Ash From A Wood Stove

The Chimney Safety Institute of America (CSIA) recommends that all ashes should be removed after the last fire of the season, as ash can damage parts of the stove if left for long periods of time.

Ash is very acidic and can also trap moisture within the stove. Leaving ash in a wood burning stove for prolonged periods of time can cause damage to the stove through corrosion.

Our Examples Of Wood Burning Stove Ash

Both my parents have wood burning stoves located in their living room fireplaces.

On one of our wood stoves, the manufacturer recommends that:

‘Wood burns most efficient on a bed of ash and it is therefore only necessary to remove surplus ash from the stove occasionally.’

Hunter Stoves

There’s no ash tray located beneath the stove and so the base of the firebox is made from the same heat resistant material as the firebox surrounds.

We typically leave around an inch or two of ash in the firebox of this wood burning stove for each fire.

Wood Stove Ash
We leave a bed of ash in this wood burning stove to help protect the floor of the firebox

Our other wood burning stove has an ash pan compartment located beneath the firebox, and so the base of the firebox is made from a metal grate to allow the ash to fall through. A handle on the side of the stove can be used to rotate the grate to allow the ash to fall through into the ash tray.

Wood Burning Stove Ash Bed
A bed of ash of in our other wood stove (there’s no ash above the grate because we had just tested the rotating grate function)
Wood Stove Grate Handle
The handle used to rotate the ash grate

The manufacturer of this wood burning stove, recommends for all of their wood stoves to:

‘Leave a thin layer of ash to retain heat, protect the grate and aid clean combustion.’

Clearview Stoves

In this wood burning stove we typically leave around 1 inch of ash on the bed of the firebox. As primary air on this stove is fed up through the grate from the ash pan compartment, too much ash can prevent sufficient air flow to the fire and can prevent a newly lit fire from getting going. (Read more about primary air here.)

Benefits Of Leaving Ash In A Wood Stove

Leaving a layer of ash in your wood burning stove can provide some of the following benefits:

  • New fires can get going more quickly.
  • Hotter fires and higher stove temperatures when combined with secondary burn.
  • Cleaner and more efficient burn of the wood.
  • Clearer glass on the stove door when combined with an air wash system.
  • Helps to increase the longevity of the stove by protecting the base.

How Much Ash To Leave In A Wood Burning Stove?

Wood burns hotter and cleaner on a bed of ash, and so many wood burning stove manufacturers recommend keeping some sort of ash bed before every fire.

The manufacturers of our own wood stoves recommend to leave at least a thin layer of ash to help protect the stove from the heat of the fire.

As every model of stove is designed differently, check your stove’s manual or manufacturer’s guidelines on how much ash should be left in your wood burning stove (if any). Try to keep to the recommended level of ash in your stove to ensure that it’s operating as per its design.

Be sure to also clear out any ash from the stove at the end of the burning season to help protect the parts of the stove from damage when not in use.

How often do you clean out your wood burning stove, and do you leave a certain amount of ash in the firebox or remove all of the ash between each fire? Let me know in the comments below!


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