I'm looking into purchasing a 1500 sf office condo in Raleigh, NC. The office is on the first floor of a 2 story, Class A masonry building. The space is 20' x 75' with 9'x 18' of low-E glass (except the entry door) on the front wall facing north. R-19 insulation on exterior walls. Interior ceiling height will be 10' for half, 9 foot for half.

I got a quote from a contractor based on a preliminary floor plan I've been working on just to see if this purchase is even feasible. He quoted a 5 ton unit (or 2 2 1/2 ton units) and that seems pretty big for a space that will have conditioned space above and on both sides of it, no heat generation and minimal occupancy. I know there are specific calculations that need to be done to determine proper sizing, but does anyone have an educated guess as to whether this sounds reasonable?

Second, I am drawing up the plans myself (as I did my other two offices and my home). In the past, the HVAC contractor

just determined what to use but I'd like to get a professional to design the system. Our house is very energy efficient and they used larger units than needed and we've run into problems keeping the humidity out of the house because the units are seldom needed. How do I find someone and what should expect to pay for an HVAC design?

Thanks!