I want to remove a 10 ft wall section to open a living room to the kitchen area. What size board do I need as a header for a ten foot span?
Impossible to say without knowing what's on top of the header. In residential construction, a doubled (side by side) 2x8 is legal when there is just a truss roof over it. I'd go double 2x10 if I had room just because I'm one to put in all of the wood I can get in there. If this is an older home without factory built trusses, or has an upstairs, a floor in the attic space, used to be an exterior wall, you better go talk to a pro who can look at the house and actually see what you have going on there. Welcome to the forum Texastom! Tom
Something else that I should have mentioned, you need to support the header with 2x studs. at least one on either end, 2 on each end is even better. NEVER nail a header to a wall without supporting it with studs directly under it. Also, make sure the studs are secured to the framing inside the wall.