I mentioned this in an earlier thread (http://hvac-talk.com/vbb/showthread.php?threadid=85094) but didn't get a response. We're adding on and replacing the HVAC, based on forum and other wisdom, I'm shooting for a Carrier Performance 13 heat pump, Infinity 80 furnace, and Infinity control.
We had load calc.s, a blower air door test, and a ductwork layout done by a third party. E-mailed the GC's HVAC sub a layout drawing before price was finalized showing sizes, register locations, and airflow per register (supply and return) overlayed on a plan drawing of the house. GC assumed a rule-of-thumb size for the equipment.
I'd always figured that we'd put the quote for the equipment the GC would've supplied against one for the system I want (higher efficiency, 3.5 instead of 4 ton), and we'd pay the price difference for the equipment. I realize that there might be a little more setup effort for the system I want. No argument there.
Well, the sub is now saying that there's something special about the system because of Manual J requirements (i.e. he wants more money). Yes, this makes me nervous that he apparently doesn't typically go by Manual J. And the drawing I e-mailed listed that the sizing was based on Manual J, as well as insulation, sealing and duct material requirements.
And my BS meter was pegged by the sub's vague statement that the air pressure or something would be different.
So here's the question: given a duct layout showing AHU and compressor location, as well as airflow, are there other complications about the equipment that I'm missing? Like I said, I understand a difference in equipment cost and maybe some time for setup, but otherwise, am I right in thinking that this guy asking for more money (a lot, according to GC) is mostly voodoo?