Help! Rough in just finished on HVAC and have noticed that air handler is different than what was originally quoted. Our original quote was for Trane XL18i 4TWX8048A1 with *AM7A0C42H31 air handler. Home is new construction, tight envelope with double pane windows. spray foam insulation in roof. 2200 sf on one level, conditioned basement with superior walls around 3/4 of daylight basement. Home is oriented for passive solar, we are in zone 6b mtns of NC. Just noticed the installed air handler is a tem6aoc36h31. heating contractor now saying oh that is better air handler because it "is metal as opposed to plastic, is tighter, and has a better HSPF rating". He plans to pair it with a TRANE 4TWX8036C1. Not what we agreed on. either air handler model or size. Our initial proposal called for a 3.5 ton Lennox 14HPX…but we wanted a 2 stage unit, so settled on 4 ton Trane xl18i. Independent Manual J load calculations were completed. I am concerned that the switch to 3 ton will not be large enough, and dismayed to have a sub contractor changing size and type of air handler without any communication. What I need help with is to understand if this 3 ton system is still appropriate for our home and if the change to tem6 air handler is a sound choice. Not sure about sizing of ducts, but will find that out if necessary. Sorry for the long post. tried to be thorough in an area that I am far from understanding. Thank you.