Just had installed a 3.5 ton am. std. heat pump with variable speed
air handler (13 SEER), 15K backup and 4" Honeywell media filter.
System seems to move more air than old 10+ SEER York system (3.5 ton
w/ 4 air handler) at standard speed (400 cfm) and am. std. setup says
setting for emergency heat mode to be 1600 cfm (450 cfm/ton). At 1600
cfm it's not only a bit noisy but seems to blow out old dust (possibly
settled in supply ducts or possibly sucked into return line, though
return line is in conditioned space except when passing between
basement and first floor through open web floor trusses. Increasing
return size is not an option due to space). Questions a
1) any problem dropping standard setting back to 350 cfm/ton in
standard mode?
2) should 400 cfm/ton be sufficient for emergency heat mode, which
should rarely kick in more than 1st stage since balance point around
20?
3) any recommended tests for locating possible duct leaks, other than
blocking all returns which could stress motor?

Thank you.