I am preparing to knock a 6ft wide opening in the dining room of our house to open it up into the lounge. I am pretty sure it's a non load bearing wall although it is made of brick (1940s construction). The question is what kind of lintel to use. Should I go for a steel box lintel or a concrete one? And how wide? Would a 7ft lintel be enough for a 6ft wall? Any help appreciated.