I've recently installed a furnace in a residential hall closet in central California. The inspector will not pass the job because there is no closet ceiling. He's telling me I have to put up sheetrock or sheet metal and seal the gaps. I asked for a building code reference and he sent me one for concealed spaces. So far that, and the fact that the local fire marshall "agrees with me" is all he's come up with. The combustion air vents through the attic space into the closet as outlined in CA Mechanical Code 2016 Figure 701.6.1(2). Is there a source someone can direct me to that shows he's wrong? I've tried to explain to him that it make no sense to put a fire blocking ceiling in and then cutting a hole in the middle of it for a combustion air but he doesn't seem to get that. I've been installing AC and furnaces in this area since 1973 and I've never seen a fire rated residential closet ceiling other than in manufactured housing. I've seen lots of furnace closets with no ceilings and most of the closets that have ceilings have vent cut through it going directly into the attic.