Cracked Firebricks

If you’ve had a wood burner or multi fuel stove for a decent period of time, chances are at some point you have experienced cracked firebricks. You may have wondered; Why have they cracked? What should I do? When should I replace? What are your rights regarding warranty? In this article we attempt to address all these questions and provide advice on how to get the most out of your firebricks. We’ll also explain why you shouldn’t burn treated timber in a woodburner. The following is a guide only, if you are in any doubt, contact us or your local HETAS engineer for further advice.

Why have my firebricks cracked?

Firebricks are a consumable item. They are therefore expected to wear out and need replacing over time. Their lifespan will depend on a wide number of factors; How often you use the appliance, fuel, operation and maintenance. Provided they are installed and used correctly they should give you a perfectly adequate lifespan.

The most common cause of damage to firebricks is through incorrect use. All firebricks, whether clay or vermiculite are designed to withstand high temperatures. During normal operation of your appliance, firebricks will experience heating and cooling. This results in thermal expansion and contraction. If firebricks are fitted incorrectly, the appliance is misused, wrong fuel used or the fire is loaded roughly, then firebricks are liable to break.

Cracked Firebricks

A picture showing a new crack in a rear firebrick.

Why you shouldn’t burn treated timber in a woodburner?

It is worth mentioning the role incorrect fuel plays in the damage of firebricks and other internal components. The use of carpentry off cuts, construction timber and treated wood is strongly advised against by manufacturers (check your user guide) and the solid fuel appliance governing body HETAS. These types of wood are treated with all manner of preservatives and/or glues and paints. Not only do they give off toxic gasses when burnt, but they also burn at a much higher temperature and rate. This puts internal components under greater thermal stress and in the event of thermal shock they will crack. Choosing to burn treated timber in a woodburner is, in a way, a false economy. It might appear to be a “free” source of fuel, but it will cost you more in replacement parts in the long term – and harm the environment.

 

My firebricks have cracked, What should I do?

Sometimes minor cracks can occur – even if you have used your appliance correctly. Hairline cracks can happen after repeated use or even in some cases upon first firing. When these minor cracks appear, there is no immediate cause for concern, and you can continue to use your appliance safely. Logically speaking, a small crack is no different to a join between two firebricks. Some manufacturers even supply larger bricks in two parts, pushed together.

A picture showing natural joins in a firebrick set.

 

When to replace Firebricks

  • If the crack exceeds 3mm in width. (Thickness of a pound coin)
  • When the surface of the brick has eroded more than 25% of the original thickness
  • When the brick begins to crumble or fall apart.

 

Caring for your Firebricks

To reduce the risk of cracks and to preserve their lifetime it is vital that firebricks are installed correctly and used appropriately. If you are unsure of how to fit your firebricks, please seek the services of a suitably qualified engineer.

Here are our top 4 recommendations.

  • Install correctly. If a brick is fitted too tightly it cannot expand under heating.
  • Do NOT burn carpentry off cuts or treated timber.
  • Build fires up gently to avoid thermal shock.
  • Take care when adding fuel. Do not throw logs or fuel against the bricks.

 

Conclusion

If your appliance has been used correctly there is no reason why your firebricks will not give you a perfectly acceptable lifespan. But, if they should crack, provided it stays within the tolerances set out above, this will not affect the safety or operation of your appliance. The lifespan of firebricks or any other internal component in a woodburner is determined by a wide range of variables over which neither the supplier nor manufacturer has sight or control. Because of the variable factors and fragile nature, firebricks are classed as consumable items. Manufacturers therefore will not cover firebricks under warranty.

See our other stove help topics >

Warranty on Stove Parts

How to replace rope seals on a woodburner door

Repairing Stove Doors

Stove Glass