I think this was answered somewhere but I'm just not finding it. I have an EPA high efficiency stove and the firebrick is cracking and falling into the box. They are more or less white clay or ceramic (probably) and line the bottom of the box on 3 sides. My questions are: what is the best replacement brick? Cost is not an issue as long as it's not astronomical. I want them to last as long as the originals (over 10 years now). Right now there is one row of standard size bricks around the box. Does it make sense to add another row or even pile them up to the top? I have no problems cutting them to fit, been using rock saws for a few decades.