The issue of bricking up an old working fireplace is that over years of burning stuff in them the bricks absorb all the chemicals etc. Then once there is no heat being produced all the stuff they've absorbed over the last hundred years starts to come out. Best thing you can do with an old fireplace is have the brickwork exposed and the fireplace recessed. Other alternative is to use lime plaster upto the height of 4ft on the actual fireplace and walls either side. Lim plaster will absorb the damp and any salts coming out of the brick.
Indeed hence my suggestion to recess it and expose the brickwork. Though if people want them bricked up use lime plaster. My house has had them all bricked up by the developer I bought it off. I will be opening mine up in the sitting room, also the one in the lounge. The lounge one I will just recess the sitting room I want a wood burning stove. Just procured a load of original Georgian doors for the house. Just need to find someone to fit the ****ers.
Chilling at home with some tunes on... Just noticed Anthea Turner on this morning looking rather hot! She's 57