This is a general guide .
http://ccl-tt.com/tips.htm
This is a base you add more as you add how many people will be in the room and what equipment PC's and such .
When I was in the industry it used to be a standard that a 10X10 Room you use a 12,000 BUT unit , yes depending on ceiling height amount of windows and if and get direct sunlight you may get away with a smaller unit .
Now I have been out of that industry over 10 Years now so Efficiencies may have changed .
That's why I suggested that you contact Genair or keep it in the 2ner family , I think that Calvin 4Everstock is still in the business .