Our real fireplace was also converted into an electric, so the original chimney space is still there. I'd think it'd be just as simple as getting the insert, and the correct flue components to go back. However, if I were you, I'd look into a stove insert instead of a fireplace. Stoves are way more efficient and better at heating than a fireplace. If you want the ambiance (and you do) then get a model with a glass door so you can see the fire.