Regardless of what is posted here you absolutely need to have a PE (Professional Engineer) look at it in person and tell you what is going on. (There is NO WAY to only look at the photos and a floor plan and tell what is the actual makeup and function of the columns.)

But I'll chime in for something to do.

Let's just say that is a very interesting floor plan design. It seems this is a one story home. I am assuming a truss roof system? Pictures of the attic might explain things.

You mention your AC is above. If those 2 columns are needed for that, I would be shocked-typically the types of systems that require structural supports are chilled water systems with cooling towers usually at large buildings.

You also mentioned a 10 x 10 structure above. Is there a loft or storage room up there? That could be possible if the truss pitches are steep enough. The dining room is at the center of the home so that could allow for the maximum area above. So the columns might be there to transfer the floor loads from the loft area. (Again guessing)

If those columns are structural, and there is no loft above, then it is possible they are supporting a girder that in turn supports the trusses. Which even then is odd; the spans based on the floor plan are not that excessive and the columns are very close together with respect to the exterior perimeter. Further, why the columns could not be hidden in the walls is a mystery. The room is not that large.

Now it is also possible that *only one* of the columns is structural and the other is placed because they thought it would look really ridiculous to have a single unbalanced column in the middle of the floor, so the architect decided to balance it with a second column. (Not that having 2 columns in the middle of a 12 x 13 dining room makes any sense either.)

Lastly the actual column size is probably much smaller than what we are seeing; it is maybe a 4x4 steel column. (Given the high ceilings, I would be surprised if it the columns are wood, even if the home is wood framed). Then back to the idea of aesthetics-nobody wants to see a 4x4 steel column in the middle of the room, so they frame it out to make it look substantial and match the surroundings.

To beat a dead horse, I am just guessing since I really cannot figure out why the floor plan is designed like that. (Everybody in the thread is guessing)

Anyway, I'll close with what I said above-you absolutely need to have a PE look at this in person and tell you what is going on.

Thanks for providing an interesting diversion to talk about

Good luck !

Please-Hire a structural engineer.

To say the joists are spaced at 16" centers leaves unanswered questions.

What is the size of the joists and what are the joists made of? (And just saying wood is still incomplete-species and quality matter for strength. For example is it grade 2 southern yellow pine or structural select, or some other wood?)

Are the joists in good condition? (Free of insect damage, water damage or cracks).

Have any of the joists been notched or bored to run pipes, conduits, ducts etc.

The positions of the loads relative to the supports matter. Where are the supports? Keep in mind the loads are probably not going to be evenly distributed across the spans. Point loads and uniform loads should be considered.

How is the second floor supported? Are there any shear connections such as joist hangers to a girder or do the joists bear on a continuous wall to transfer the loads to the foundation?

The deflection and stiffness of the floor system should be considered. It might be strong enough to support the loads, but might be too bouncy or bend too much resulting in a wavy floor.

Consider *all of the loads* meaning dead and live. Oftentimes an oversight is that only the weight of the *objects* placed in a room is considered. What happens when there are also people standing up there playing? And again consider where all loads will be relative to the supports.

So back to my original suggestion-please consult with a structural engineer.

Good luck and hope it works out for you!