I have a Regency firewood insert (Large) which I had it installed about 15 years ago and have been using it every winter since burning about 5-7 cords per season. Every other year I have the chimney cleaned and this time they said I had couple of firebricks to replace. The 2 to be replaced were at the back wall and when I removed them I noticed all adjacent brick were also cracked plus I had 2 cracked at the bottom.

I needed total 5 new bricks for the back and 2 for the bottom. Got 7 new brick but 3 needed cut to fit. I used a hacksaw which happened to be fitted with a 24 teeth blade (not sure on the exact teeth number) and it went really good. Also used a rasp wood file to make minor adjustments and that worked well. These bricks are very easy to cut but have to be careful cause I think they are fragile