Thirteen thousand butes is more powerful than the largest home window unit I've seen at common stores, like Sears. It's much more than you need. I handle rare A/C needs by setting the smallest 5,000 BTU unit in to my Scamp's vacant refrigerator
space. With a few small fans to circulate the air, it can drop the temps by 30 degrees in a few minutes. It only cost me $40, used. You need to save the roof space for a nice high-powered fan, too. My MaxAir fan, on high exhaust, can suck the window curtains up to a 45-degree angle!