Re: what size support header needed
rjr ... There are some things that can't be answered over the INTERNET sight unseen .... this is definitely one of those.
What you are describing is a beam and not a header and is a critical requirement to be appropriate for everyone involved .... the building inspectors , your home insurance , your personal safety.
When it comes to structural integrity and safety you need someone qualified on site to determine what is required for your situation. Hiring a professional like an engineer is really the way to go. They would be able to provide the options available as well certified drawings which when having their endorsement is like ****.
Just a thought.
"" an ounce of perception -- a pound of obscure "