I stayed in bldg 18 last year and even though it is tagged a "smoking" building. I would have never known had there not been an ashtray on the table. There was NO smoke smell at all in the room.
However, I do understand the problem if you're travelling with asthmatic individuals. While I think that the location of 18 is perfect, I'd suggest 14 or 15 if they are non-smoking. They're right next to 18 and close to the main bus depot, and the main building.