The 10' rule... unfinished basement

Ranch, unfinished basement. Natural draft furnace, and natural draft WH next to it. This return looks to be approximately 10’ away from furnace (I didn’t actually measure it.)
I felt suction at this return. The other return is in the hallway on the floor above. So this is not the “sole” return. Is this still a back drafting concern? Is an unfinished basement still considered to be in the same space? And if its no concern in this case, would it be a concern if the return would be closer to the furnace? If I’m off base here please direct me to the proper place to do more research.
Thank you.

I cannot tell from the picture the distance from the return grille, but it does look like it’s 10+ft. If I could not tell by eye that the distance was easy 10+ft, I would measure it. Anything less than 10ft+ would get reported. Furthermore, you must have at least equally sized supply ducts in this basement. Otherwise, no problem.


Is that chimney going through a return air?


Wow, Marcel, great question. I was wondering why the chimney vent was routed like that.