Very Ruff Sketch of my proposed Fish Room

[flowerseller]

I run 250w MH's on my 400g system located in my basement.

I need a chiller.

[Origami]

I run 2 x 250W MH on over a frag tank at night (reverse light cycle) and 720W of T5/VHO over my display during the day. The system holds about 350 gallons and is located in my basement (no walk out) and has a pretty good amount of surface area for evaporation. I don't have a chiller and the temperature remains fairly stable (about 1-1.5 degrees per day is typical), evaporating around 3.5 gallons per day. I can tighten my temperature control to within about 1/2 degree if I add a fan over my 100 gallon Rubbermaid sump to increase evaporation. (If I had better thermal contact with the basement floor, I could probably dissipate more heat through the slab than I am right now, come to think of it. But the Rubbermaid has a built-in platform of sorts that limit this.) If I try to run my frag tank and display lights at the same time, the lights provide too much heat loading and a chiller would probably be required in my setup.

 

As for the window A/C, I agree with Craig, while it helps with humidity, you'd just be dumping heat into another room. Venting the heat would be required and this is better suited to other types of AC units that allow for separate venting. If you're going to go to the expense of using the AC to keep your water temp in check, I'd look at adding a chiller to the mix instead since it's designed for the purpose.