Here is a look at an insert. These fit into your existing masonry fireplace and are a great option after a chimney fire or for more efficient heating of your home. This insert was bought and incorrectly measured by another company. I installed it and to make it fit right I added cultured stone to fill the gap between the insert and the fire box. Inserts should fit flush with your with your existing masonry. The bottom picture shows the top view of the chimney where the liner is connected to a top plate and then a rain cap. This keeps water and animals out of your chimney. Liners come with a lifetime warranty from the manufacturer.