Using Solid Fuels and Cast Iron Thermal Discoluration

Fossil Fuels and Thermal Discolouration

Unfortunately, thermal discolouration to the firebox is inevitable and almost immediate when using solid fuels like coal in a cast iron fireplace or insert. Use propriety high temperature paint to re-coat the affected areas of the firebox or for the more

traditionalist amongst use black  graphite polish to protect these areas. If using the more traditional black graphite polish to maintain and protect the firebox of your cast iron fireplace or insert this will need to be carried out far more frequently than if using the more contemporary high temperature paint. 

If you are burning solid fuel i.e. coal in your cast iron fireplace there are a number of other issues and basic maintenance procedures you should be aware of.  There are some extremely high temperature burning fuels such as Petro-coke based coals which can cause damage to any fireplace please check the fire place manufacturers’ recommendations or refer to the Solid Fuel Association ( t o identify the fuels which are most suitable to burn in your cast iron fireplace.  Always use an approved coal merchant as your supplier. To help minimise any damage to your cast iron fireplace from exposure to excessively high temperature fires it is recommended you install an inexpensive clay fire back to help protect the cast iron.

The grate component of your solid fuel burning cast iron fireplace, or insert, is a consumable part and may need replacing from time to time depending on how often you have a fire and the temperature of the fires you burn. It is important if using coal as your fuel to empty the ashes daily or immediately before the fire is lit. This will help prolong the life of the grate as any build up of ash beneath the fire and grate will cause the grate to burn out more quickly.  You will also need to control the air flow or draft into your fire through the air vent or chimney throat plate as an excessive draft will cause the fire to burn too hot wasting fuel and potentially damage the fireplace or insert and considerably shorten the life of the grate (for more information see our article, The Ultimate Guide to Keep a Fire Burning in your Fireplace or Stove).   

Finally, it is you responsibility to burn smoke free fuels if you live in a smoke free zone.  

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