this calculator has a great rep around the www. I find it super useful, and love the way it graphically depicts the hot/cold spots in a given set of dimensions.

I'm not sure if the site itself automatically detects your on a mobile device or not, it seemed to know I was on a tablet, I don't have a computer set up yet so I can't say for sure. Either way, punch in your room dimensions, and take a couple minutes to look at what ya got. It's fun! Lol if your a geek like me.

http://amroc.andymel.eu/?l=15&w=12&h=8&ft=true&r60=0.6