Typical 'rule-of-thumb' for header/beam is 1 foot span for each inch high for 4x wide or doubled 2x with 1/2" plywood sandwiched between them, 4 foot minimum length, i.e., doubled 2x4 with 1/2" plywood sandwiched between them (may not even require the 1/2" plywood based on my memory, but to be safe, I'm including it) will span 4 feet.
Likewise, a 2x6 = 6 feet; 2x8 = 8 feet; 2x10 = 10 feet.
Now, though, that would typically be for SYP (southern yellow pine) and we are probably looking at SPF (spruce-pine-fire), so we need to compare the strengths of those two species of wood together.
Southern pine and a Modulus of Elasticity of about 1,800,000 for #1 grade, SPF has a Modulus of Elasticity of about 1,500,000 for #1 grade - not a major difference. Not like Northern white cedar which has an E of about 800,000 for #1 or Ponderosa pine which has an E of about 1,200,000 for #1.
Now, though, we are not talking about ONE doubled 2x10 beam, there are TWO doubled 2x10 beams there.
So I doubt there will be much problem with the 'beam', now, though, 'bearing' comes into play.
SYP has an
Fb of about 1950 while SPF has an
Fb of about 1400. That means that the fiber bending (crushing of the bottom of the end of the beam under load) of SPF is more likely to happen with the load as SYP would, however, separate that load to TWO beams and the load is reduced by half, so that may not be a problem.
Typical bearing is usually at least 1-1/2", and a good rule-rule-thumb is bearing distance should equal beam width, so, a 4" wide beam should have 4" of bearing.
The above, of course
, is open to challenge and change by actual structural engineers who can do the calculations instead of using 'old carpenters rule-of-thumb'.
Thus, in my NOT AN ENGINEER OF ANY TYPE opinion, that is probably okie dokie ... depending on the end bearing depth.
Brandon, what say you?