thomas rubino wrote:.....7.5 "x 7.5" square with a 5 gal pail as a feed tube extension... end of season the feed tube was the size of a 5 gal pail. !!! I had to keep the feed tube partly covered to draft. In our greenhouse during the winter the fire stays going all day, many days my wife is in charge .... seems that if you force wood into a feed tube made of a soft substance it crumbles... therefore making more room for wood. My next core I used soft insulated firebrick ,thinking that they would hold up better than perlite... nope, seems that if you force wood into a soft firebrick you can make it wear also. My next core was my first with hard firebrick , but I did not bring the retaining walls up past the top of the feed tube... seems that you can break the bond of fireclay if you force wood into a 7.5" X 7.5" square hole without proper support ... my current core is hard firebrick and the clay brick surround is cemented and is above the level of the feed tube... winter is almost over and guess what seems that you can't force wood into hard firebrick feed tube that is surrounded by concreted brick ! Bottom line , the cast core was by far the Superior material to build with but... it is fragile ! In an insulated home where you are sitting near your rmh and your fire does not need to stay going 12 + hours a day it would work perfectly. If you search my posts you will find pictures of all rebuilds.