I have a Harmon accentra insert 2012.never installed. I am installing in new construction hearth .Its says I need a zero clearance box. Parts# 1-00-674070 .I cant find one and Harmon says they know longer make. does anyone know is the 52i zero clearance box is the same? will it work with the older accentra ? If not how does one install ,safely, with out one, non combustible material ect?