Heat Load Software
I've been using Slant Fin's Heat Loss Explorer for years, in addition to an Excel spreadsheet that I put together based on John Siegenthaler's formula in "Modern Hydronic Heating".
I was recommended to Wrightsoft's Manual J software. I took a look at it. . . it seems very powerful, and worth the price, but it has a heavy emphasis towards HVAC. Furnaces, CFM, etc.
What software are you using?
Keith