Ok , I am getting ready to install a pellet insert. I already installed a pellet stove in my back fire place. It was easy, took the fire place cover off found I had an 8" stove pipe already there. So I ran a 4" stainless steel liner up an out. Now I want to install a pellet insert in the front fure place. So I took the cover off expecting to find another 8" stove pipe. But no , I found this. An 10" clay pipe , coming up from the bottom and going about 2' up into the chimney. It ends there and is open. What is this, the house is 108 yes old. When I look under into the craw space all I see is a bunch of stone from where I guess this pipe originates. so what is this and can I remove to install my insert.