Hi, I can help you with this. Can you verify that the joists are 15' on each side of the beam and that it will support two floors? What about an attic?
Before we get started I'd like to point out that a Professional Engineer's standard of care typically includes a site visit to assess field conditions and get an overall understanding of the structure. This can obviously not be accomplished through the internet. The information provided here is meant for informational purposes only (general sizing and budgeting) and is based on the information provided by you. The information should be verified by a professional engineer who can visit the site to ensure that potentially important information has not been overlooked or omitted.
You can plan for a 5-1/2" x 14" Anthony Power Beam (min Fb = 3000 psi and min E = 2100 ksi). A 3-1/2" x 14" works for strength, but deflection is a little higher than I would like to see for a main beam.
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