I was called to investigate a system installed by another company as the owners were having problems with spillage of smoke back into the room. Upon investigation I found a few things that were less than desirable about the installation, but the main culprit for the spillage was heavy tar build up in the liner. The liner diameter had been reduced from five inches to about two, due to the tar. After speaking to the customer it was established that they burn quite a lot of pine in the stove and they also like to close down the air controls to get a long burn out of the wood. I explained to them the importance of burning the wood cleanly, which means to burn it hot, this is especially important with a resinous wood such as pine. I cleaned the liner out and did a couple of things to rectify the other fitting faults. The stove is now running well.