[turtlebits]

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.

[bizzz]

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).