I have a question about the heating setup in the house I am renting.

It is a two family, split house.

There is no AC, accept for window units.

We noticed the smell of cigarette smoke, and found it was coming out strong from the return registers. The guy on the other side smokes.

I noticed on the return line, the line coming from the second floor, there is no duct-work. In the basement, the extended plenum runs out, with round pipe to the first floor supply registers.

The second floor return, runs up to the small second floor hallway, inside the wall, with no duct. Just the inside of the wall up to the space between the hallway and the bathroom, and actually when I took off the register, the opening comes up under the bathtub. Which there is a large space under there, and is likely how the smoke is finding its way around. Through these ductless passageways.

This isn't one of those new ductless systems, I just wonder how typical this is.