Stovax solid fuel stoves

I haven't a stovax but the Rais insert is similar. The stovax insert seems to have inner and outer components so much of the heat is not transferred to the outer frame in contact with the plaster. Insulate the sides and top of the box at installation. The outer frame is wider than the ope so the edge of the plaster is not visible. You can touch up with pollyfilla once installed - it can take pretty high temp just above the stove. You may get some blackening of the wall above the insert though.