I found an Avalon Newport Insert for 1300, still sitting on the pallet. Guy said it was purchased ins 2011 and the land contract owner said he couldn't install it. It's been sitting in a basement since 2011, cords still tied up, on the pallet. Includes 20' of liner. I have a Greenfire insert in one of my fireplaces now, I am debating on moving that to our basement where our master is. That chimney is an interior chimney, the greenfire says it's acceptable to run the vent partially up the chimeny. The chimney does have a rain guard on it and is in good working order. Can I then just stuff the damper with rockwool and put a block off plate up to seal it? I don't really want to purchase AND run 30+ feet of 4" liner. The new avalon would just go in where the greenfire is. That has a full run liner but no block off so I thought I'd stuff some rockwool in there too?