Hi. What size concrete lintel would be required to safely support the brickwork in this chimney. The width is 800mm. So, I understand that 1000mm lintel is required. What I can't quite get my head around is the dimensions of Width and height. Would a 4" X 3" lintel suffice. Or 6" X 3". I've looked at how to calculate lintel size requirements but struggling to find info. Many thanks.