Q. Can an inadequate (small) flue be replaced with a larger to create a better draft? We have a very narrow firebox and our current flue is too small for us to use the fireplace safely.
A. larger flue size can be installed in a chimney by removing the flue lining that is currently in use. This will need to be done by an experienced chimney technician.
The technician will remove the existing flue tiles using a set of tile breaking rods which have an offset steel head, that attaches to the rods, then the rods attach to a drill. The drill whips the head around inside the flue and bashes the flue lining into manageable pieces. The debris is then removed from the base of the flue.
Depending on how much space was left around the flue and any sort of debris that was tossed in after the flue was in place (back fill/infill), you can gain quite a bit of extra room, to fit a larger liner in. The person removing flue does have to be careful not to damage the remainder of the chimney, i.e. bricks, blocks, adjacent flues. After removing the flue lining the chimney should be checked with a video scan, to make sure previously hidden issues that could not be seen, like combustible materials, can be addressed. After that, a new liner can be put in place.
Sometimes there is not enough space in the chimney to gain the size required. In these cases you may be able to solve the problem from the other end by installing a smoke guard shrinking the firebox opening by adding new masonry.