If this is a manufactured wood burning fireplace, you will need to confirm that the fireplace was safety-tested and approved for use with a ventless system by locating the make and model number information of your existing fireplace. If the fireplace was approved for use with a ventless gas log set, you will need to check with your local code office to ensure that ventless gas hearth systems are allowed in your municipality. If the manufactured fireplace was approved for a ventless gas log set, and if ventless systems are allowed in your area, then you are able to install either a ventless gas log set or ventless gas insert of your choosing after measuring the front width, rear width, depth and height of the fireplace opening and comparing your measurements to the minimum opening requirements for the ventless gas log set or insert you are interested in.
To answer your question, a locally-licensed plumber will need to run a 1/2" cast iron pipe stub into the fireplace opening per both local and national fuel gas code, in addition to a manual shutoff valve a.k.a. key valve on the wall or floor adjacent to the fireplace opening. When installing a ventless system inside any wood fireplace, you would simply close the damper.