I had a RFS Opel 2c with double glass doors installed in my house in 2018. Since the beginning, after as little as an hour burn time, the left door window will start to fill up with soot. After 5 hours, it is almost completely blocked. You can stand right in front of it and not be able to see flames. The right hand door will get a little build up in the lower corner after burning for days. I am not getting much cooperation from my installer, United Brick & fireplace. They don't think it's anything to do the door itself. They tried an extension on the flue, no difference. Talked to Rfs directly, said they hadn't heard of this issue. Anybody familiar with this problem?