Question: We want to put in a Majestic superhearth 36" fireplace. The people at the shop tell us we cannot put this into a lined block chimney and have to use a metal chimney of a certain code. Why can't we use a lined block chimney? Answer: Most pre-fab fireplaces are listed to be installed ONLY with the campanion chimney made by the same manufacturer. The chimney is designed with the system, and often is important to the cooling of the appliance walls. This is what allows the unit to be "Zero Clearance" Your dealer is right !