I have a 2 story home. There is a 48" wide opening in the first floor inbetween dining and living rooms. The opening passes through a load bearing wall at the middle of the house. I would like to enlarge the opening by 2'. There is a steel beam below the load bearing wall. I watched the video on installing a double ply 2x12 header to transfer the weight down to the floor. What size header do I need to install to safely distribute the weight.