We moved into a downsized place a year ago. There was an old Majestic Zero Clearance FP and a PO had converted it to gas by adding a 40 kbtu gas log. Last season we never turned it on as with the pinned damper it was a pretty picture, but 40 kbtu up the pipe. It is very common on these 80’s houses to build a 2x4 framed chimney into which these ZCFP’s were installed. I found probably the last of the Rinnai 750 fireplaces to install. It was a bit dicey cutting the FP out with two stories worth of chimney overhead and working alone, but I was able to handle it safely. The Rinnai is low 80’s efficiency wise with a programmable stat build in, modulating was from 5000-30,000 btu and a modulating and quiet fan. The remote is kinda wonky, but we have it figured out. We haven’t run the oversized central furnace since installing this thing. One of the things I most appreciate on this is the vent is small and right out the back. I intend to open the wall in the 2nd story bedroom and frame in a closet space in the abandoned 2x4 chimney chase. Can’t have enough storage space and the chase is empty, so , why not? Anyway, it has been an excellent addition to the house. The direct vent termination pictured is 5.5” in diameter.