We have a Majestic RHE25 RN gas insert fireplace that is directly vented through the chimney. We are wanting to reface the wall that the unit is on (currently stone). We have a question we cannot find an answer to. When framing the drywall, how much non-combustible clearance do we need on all sides of the unit? We have downloaded the manual. It looks to us like the framing stud above the unit is directly above it. Thank you for your help.