I have a friend who has a wood stove going into his chimney, which is below grade. He'd like to remove that and put in a pellet stove. I went to a stove store to inquire about that and they told me he'd have to redo his chimney because the wood stove would normally use 6" pipe and the pellet stove uses 3" pipe. I'm guessing it's not as easy as putting a 6x3 reducer at the chimney thimble? Since his current setup is below grade he knows he can't just go out thru the wall with the pellet stove smoke pipe.