Here's my first post, I have been roaming around this forumn for a few weeks. I just bought a house and a pellet stove to put in it. The house has a brick faced wall in the living room with a 6" thimble and a clean out door below it for a wood stove. I want install my pellet stove in the same place. There is a brick chimney, that i want to run my vent pipe in thru the existing 6" thimble. My question is that when I removed the cap plate that was installed over the thimble when the wood stove was taken out, I looked up and about 4 to 6 inchs up from the thimble is some sort of grate. what is this grate and is it removable so I can run my vent? I tryed searching and I can't figure it out. The stove I bought was a USSC 5500M from TSC.