If you've got a log burner or a multi-fuel stove, then chances are that, at some point, you've noticed one or two cracked firebricks. You're in the right place if you're wondering why it happened and what you should do about it. Keep reading to learn more about why cracked firebricks happen, what you can do to prevent them in the future, and what to do if you find one in your wood-burning or multi-fuel stove.

How do firebricks work?

Wood-burning stoves are an increasingly common method of heating a home. But even if you have had one installed, you might need to catch up on how it works. Many people with a stove at home add their fuel, light it, and enjoy the warmth without overthinking the specifics.

Wood-burning stoves have firebricks that are in place for two main reasons. Firstly, they create a space for air to flow up the chimney, creating a draught and making the fire hot enough to produce enough heat to warm the room. Secondly, the bricks absorb and radiate heat as your fire roars. Absorption and radiation help retain the warmth in your room, even after the fire has died.

Why do firebricks crack?

Most firebricks are made from vermiculite board or fired clay. Vermiculite reflects the heat into the stove, while clay tends to be better at retaining the heat. These are the two most popular materials, although some firebricks are Thermotte, a type of reinforced concrete, or cast iron. In this article, we'll assume you have either vermiculite or clay firebricks.

No matter which material your firebricks are, like all internal components of your stove, they are subject to thermal expansion. Over time, the materials expand and contract due to temperature changes. Sudden or rapid changes in the temperature can lead to cracks in the firebricks.

Heavy impact on the bricks, poor fuel, and incorrect fuel loading can also lead to cracks in the firebricks.

What to do if you find a broken firebrick

Discovering that one of your new firebricks has a crack while loading your stove with fuel can be a worrying situation. However, the good news is that you don't have to panic. Firebrick cracks are not uncommon and are not usually a cause for concern. A small break in a firebrick isn't very different from the joins between firebricks, and with the proper care, it can last for a long enough time, even when cracked.

If you find a crack in one of your firebricks, the best thing to do is keep your eye on it. There shouldn't be any issues if the damage remains small (around 3-4 mm at the most) and remains stable over time. However, if it's worse than this or deteriorates over time, you should be prepared to replace it.

When to get a replacement firebrick

There should be no urgent need to replace your cracked firebrick if it remains stable and isn't exposing the stove body. You should swap the firebrick if it's starting to crumble, is showing the outer body, or is not staying in place.

How to replace a broken firebrick

Over time, all firebricks will usually need to be replaced, although they will last a while before you do this. You can usually purchase firebricks directly from the manufacturer or from a stove spare parts specialist. To install a new firebrick, you first need to remove the old brick or bricks. Your stove’s manufacturer’s handbook will include instructions on how to do this correctly.

Then, clean out the area where the old firebrick was. It should be free from debris to ensure that the new firebrick sits in place correctly. Follow the manufacturer’s instructions on how to fit the new firebrick.

Are my firebricks under warranty?

It can be frustrating to find that an almost-new firebrick has cracked. But unfortunately, bricks in stoves are rarely under warranty. Since they are subject to much wear and tear from extreme temperature changes and logs thrown at them, you're unlikely to get a replacement for free, even if your brick is new.

Can you prevent cracked firebricks?

Since firebricks are exposed to extreme changes in temperature and often lots of heavy use, there is often nothing you can do to stop them from cracking. However, there are some steps you can take to reduce the risk.

First, it's essential to ensure that your firebricks are correctly fitted, as incorrect fitting can make them more prone to damage. The best way to do this is to have your stove installed by a qualified and reputable professional.

Take care to build up your fire slowly, as an extreme change in temperature, going from a cold stove to a roaring fire, can be one of the leading causes of cracks in the firebricks. And always make sure that you are using the correct fuel and load it carefully and gently to avoid impact on the firebricks. How you load and light your fire can reduce or increase the risk of cracked firebricks.

There is no need to panic if you find a small crack in a firebrick. You can expect some wear and tear. And if the firebrick is not severely damaged or no longer staying in place, there is no need to do anything – it should work just as well.

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