Love the great info on the site, been a reader for a while. Had a basic question......

I did a quick search and didn't see anthing definitive, but I appologize if this topic has already been covered. My background is in industrial systems, and it is typically very easy to get installation and engineering data for commercial and industrial equipment.

I'm getting rid of my window shakers and putting in a central air system. Like I did with my boiler, my plan was to size,specify, and set the equipment myself then call in a tech to do the final connections, charge, and commissioning. I was suprised to find that there is limited or no data available to compare the different offerings (only checked trane and carrier before getting frustrated). I did do a chat with a customer rep from trane who would send me a specific unit's info within 24 hrs, but this is a pain when I just was to do a quick compare. I was wondering where the professionals get their info to size customer units? Just seems odd that its easy to get info on 100 ton DX units but not a little 2 ton residential. Thanks in advance!