Good point for standalone houses! I live in an apartment, so everything you listed is backed by some concrete blocks. So, realistically speaking, the air in any meaningful amounts can only come through the window/trickle vent of the door.
You'd be surprised where air can leak in. Your house/building is not a closed system. You should assume that any/all wall penetrations will infiltrate air, via electrical wiring/conduit, through insulation, plumbing, hvac ducting.
Thank you, I did not consider it, but looks like positive pressure is a best practice and I'll be looking into that (mounting fans directly onto the trickle vent).
