Bought this house new 12 yrs ago with a builder installed Majestic UVC36, NG Non-vented fireplace. The heater works great but there has always been an annoying smell when lit. It sort of smells "sour" and we have been putting up with it since new. Filters cleaned every year per the mfg instructions, logs carefully placed as instructed etc. Last year, I even called the local gas company to come and check it out, his inspection revealed nothing wrong, took sniffer/meter readings, all were well within specks. We have a Co-2 monitor installed, never has alarmed, but I have always had to remove a normal smoke detector in that room to keep the whole house from alarming. After 11 years, changed all the smoke detectors to an "improved version", and within a minute, the SD will alarm. So...I think I would like to change this insert out to a vented version, this summer, hopefully some will be on sale???. The vent is the biggest question to muddle through. On top of this heater is a cove that is the same width as the stove and about 2 feet high, 2 feet deep. Hate to have to run a vent up through the middle of this (to the roof, approx 15') as the wife is giving me the "eye" about it, can run to an outside wall, on a porch and either leave it there??or elbow it up through a 4 ft wide soffit to the roof. In either case, what type vent would I use, double inner/outer (one for input air and one for exhaust)??. Just in the planning stages right now, appreciate any thoughts.