I have my sump room in the basement under the stairs, so pretty tight quarters. I actually run two display tanks (100g upstairs, and 135g on the other side of the wall) now from the same sump (still ample capacity for power outages). I also have a refugium/QT (out of view on the left) in there, that I can convert to another sump if I want. It can be connected to my main sump with an external overflow. I have all the necessary drain and water supply (incl RODI feed line) plumbing down there too, as well as all my dosing stuff.
In the sump, I have a Vertex In-280 skimmer, Vertex UF-20 bio pellet reactor, DIY ATO, and a single Sedra KSP-20000 (2000gph) return pump that runs both tanks, with T offs for my bio pellet reactor, chiller (1/3 hp Artica), and external GFO/Carbon reactors. I do not use any heaters, and tank temps are constant at 79 F.
I like it, because all the noise is out of the way, and less chance of any disasters upstairs to ruin hardwood and carpets.
