We have a beautiful stone masonry chimney and dislike the idea of putting a large vertical termination cap on top (from an esthetic point of view). Rather than installing a sealed gas insert with co-linear venting, can we put a B-vent unit inside a masonry fireplace and terminate the single liner shy of the chimney top? We're not concerned with the lesser efficiency of a B-vent unit as we only want the insert for its ambiance.

What would be the possible negatives in doing this?