Complete set of vermiculite for your Viking 30 or JD320.
Vermiculite is a high temperature resistant material used for thermal insulation. The material is pressed into discs and is often found in ovens, stoves, boilers etc. Vermiculite parts can become worn and sometimes crack, affecting the insulation. It is therefore important to replace them. How long they last is difficult to predict as it depends on how much you burn and whether you bump into the tiles with the wood.
Here is a manual on how to switch: Click here!