Just had my chimney swept for the first time since I got my Jotul wood burning insert. Anyway, the guy tells me that the company that installed my insert used a "cheap" single wall stainless steel liner, and that they should have used a better double wall liner. He then quoted me $1300 for a new double wall liner. Besides the fact that I'm not looking to waste money, is there any truth to this single wall versus double wall business? IS there really that much of a difference in terms of performance or safety? Please help.