To either side of my fireplace there are two very old windows that were covered with plaster. This is a north facing wall. I believe we get a lot of heat loss. The view on the other side is a brick wall. There is no reason to have windows, except for maybe letting light in. Problem is the plaster is cracking. There are two ugly cracks that go the length of the wall---each one in the center of the old windows. I am thinking about removing the windows and plaster, and replacing with glass block. Would this be a good idea?