I know I am late here..but if you decide to do this I would suggest having the tank against a wall running across the joists in the floor, not parallel to. If you could locate the plans to your townhome you may be able to see which way they run. I just put a 125 above my crawl space and could see how my joists run from underneath the house. My father-in-law worked in building/construction for many years, and he helped me get the tank in place and looked at the joists. He thought it would be fine. 125 is the biggest I would personally go on a 2nd floor..the best way to figure this out though is speaking with a building engineer.