Fireplaces, Heating Stoves, Flues and Chimneys - replacing fireplace with wood stove.

Thank you for any insight/help received. I currently have a fireplace insert within a box that slants away from the wall approx. 3 feet so that it faces one room and not the other. It is a monstrosity of a firplace that overcomes both rooms. My house is a split level home with 800 square feet downstairs and 800 square feet upstairs. My problem is it takes up way too much room and would rather have a more efficient, space saving wood stove. I know, or I think I do, that the box that houses the fireplace would have to be torn down and a hearth built in it's place. What I do not know is can I use the existing chimney as is for the wood stove, or reline it with a smaller insert or tear the whole thing out and put in another? The chimney runs interior of the home from downstairs straight up to the roof, I would say it is approx. 12-14 inches diameter flue size. I'm not sure if it is double wall but I believe it has to be for the proximity it comes within combustible surfaces. I can measure the actual flue size if need be and find out if it is double wall if neccessary. Would appreciate any and all input for this project.