Got a Century CW2500 installed before the end of the season. The fireplace was smelly before liner installation, I ask them to clean the chimney with chemicals but the installer said it may damage the flue. I didn't do it based on their feedback. 2 months later, on a warm day, we smell it again on warmer days. Sniffed inside the stove, nothing. Took the shroud out and found the walls of the fireplace is still smelly. Here is the puzzling part, I clearly remember the walls were fairly greyish in color but now seems like there's a coating of black stuff sticking on the surface, does that mean the liner wasn't installed properly and leaking back into the fireplace? If not, what would yall recommend using to effectively clean the buildup off of the fireplace?