Anytime you start a fire on a cold day after having to let the stove go cold for whatever reason. I had to burn down the rest of my morning loads coals this evening. I had a new cat arrive this week and just could not let it sit in its neat little box anymore! It is a sud-chemie stainless steel cat. The company has been making them since the 70's in Needham, Mass. I got it from Ebay for $59 inc. shipping. Thanks to a tip from Raybonz. Wood burning bliss is the first fire with a new SS cat that cost $59! These things light off like a funny car! Fast and easy!