So I need a bit of advice. I have a 1989 Majestic MBUC36 prefab with an 8" flue and I am looking at getting a Hearthstone II with 6" outlet. Spoke to the local Heating and Air folks and they said I would need to add a 6" liner and fill the gap with some concrete/vermiculite like substance costing $2700. Spoke to the local city code enforcement and they said drop a 6" liner like easy flex, cap off the gap at the top so no embers or anything get back inside and you are good to go. Is the business trying to up-sale or is the code guy the one full of something other than concrete/vermiculite?