I am having my two A/C units replaced with two 2-ton Infinity systems. In order to get more air into a couple of rooms that were always hotter with the old system, my HVAC tech is replacing the current ductwork going into those rooms with larger ducts, running them directly from the air handler to the registers. The concern I have is that he is not replacing the registers, and is running the larger 7-inch ducts into the existing 5-inches registers, joining 7" into the 5" near the registers. I know that this is not the right way of doing it, but should I be concerned with this set-up?

Any input would be greatly appreciated.