When you first take delivery of your new fireplace or stove there is a little leaflet with the cast iron fireplaces this tells you about Care and Maintenance of your fireplace. It is normally in the bag that the fireplace comes with, basically it tells you how to keep item clean etc and what not to use on it. It briefly mentions tempering a fireplace, which is something; I am going to explain so you don’t make a costly error.
When the fireplace arrives it has been transported and stored for a long time since it was originally cast. Cast iron will absorb moisture from the air so when you first light the fireplace its very important you DO NOT build a huge fire as this will just simply crack the fireplace as the cast iron need to be tempered first. This process involves lighting a small fire with wood for two or three times gradually building it up each time until after a few days the fireplace will be tempered and you can then start to use Coal etc on it or have larger wood fires. It really is important to follow this process after the fire has been stood for along time i.e. over the summer as the cast iron will again need tempering before daily use. Stoves are more prone to damage by not tempering properly as moisture will build up in the brick linings and as it’s sealed with the glass door you tend to get more moisture build up. I would recommend having a week of small fires in the stove to make sure that before you load it up its well tempered and ready to handle the large heat outputs that they generate, just a quick note on the bricks don’t worry to much if these crack as long as it doesn’t crumble away there simple to fix with a little fire cement saving the price of a new set. That’s all there is to tempering and if you follow this simple process you can be assured that your fireplace will last a lifetime.