I think the pipe is 4 inches wide. But I'll have to confirm this. In the meantime, I carefully read the manual for my stove yesterday. I noticed something I had not seen before. There's a diagram for the right flame pattern. The only difference between the diagram and the flames in my stove is the size. The diagram flames are much smaller. Ever since I've had this stove, even before the work on the vent, the flames have been large. There is also a diagram for how the logs are supposed to be set up. It matches my logs. In any case, I have located a fireplace repair and maintenance company. I've just contacted them and hope to hear back soon, though we're now getting into the busy season, unfortunately. I want them to check out my conversion kit which is propane to natural gas (whether the correct one was used. If not, I located a company online that claims to have the original kit for my stove), the soot problem, and how a wall thermostat can work with my stove as opposed to the remote control which has a number of features. The manual states that the stove can run on a thermostat and gives instructions and a diagram on how to make the connections and the wire/gauge needed. All this thermostat info matches what some of you on this forum informed me a while back. I was really grateful for the advice.