No problemo. I did cite him some rules of thumb that I've run into but I hope I made it clear when I used the word "guess" that he would get a HVAC guy. I just wanted to give some general guidance. Most of the pros I know have done the calculations so much that they establish their own rules of thumb and unless a house has lots of extra windows or cathedral ceilings, etc., they don't do the calculation.
That said, most DIYers don't do HVAC and duct installation anyway so he was probably headed to a pro. I noticed on a HVAC forum the other day that a pro in florida uses 600 sq.ft which would then be about 2 tons for this one. I think of florida (disney world anyway) as being hot and humid and would need more cooling but I guess the pros understand the factors in their own locale better than I do.
In my family, my uncle was the hvac and plumber (besides general carpentry) and he didn't take me out on all those jobs doing the hvac work so I know about enough to be dangerous. My cousin is the hvac and plumber now. I grew up in a small town family construction environment where we did everything when building a house(no subs). I started as a kid as soon as I was old enough to hold a shovel and dig footings. I eventually moved up to hammering nails and really graduated when they let me saw boards(with a hand saw of course). When doing brick and masonry work, I got to mix mortar. My grandpa was the finish carpenter and cabinet maker. Sure wish I would have learned more from him. Catch you later.