I'm going to be installing a patio door between 10-12ft wide, which will knock out quite a few studs. The wall supports a second story above. Since this is in a basement with a low ceiling, I'd like to have the narrowest header that would be sufficient to support that size of a door opening. Ideally, it would be no more than 6", and preferably closer to 4". I'd be willing to use steel I-Beams if it were possible to, but if I have to use wood for the header, what would be recommended? Also, if steel I Beam recommended for header, how can I attach the I Beam header to the supporting studs? Any suggestions much appreciated.
You can pick up advice here, but you really need to have a first hand look from a qualified contractor or inspector. You will not get a 4 inch steel I-beam to carry that load you propose, but maybe a 6...maybe. Lots of factors will be in play, such as the load above being in a gable end, sidewall, or if any of the load is carried by other factors.
I agree with joasis but one posibility is to replace the rim joist with a header then joist hanger the joist off of that. It will be alot of work and you will have to support the load above temporarily while it is being installed.