Heat pump--variable speed cfm/ton settings

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 are: 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.
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They (AM STD) Must have really changed their equipment in the last few years. I have a 5 ton with variable speed air handler. I had choices on the driver board with some dip switches. Was pretty simple to choose the program I wanted. Been running great for 8 years. For cooling I choose, ramp up to 30% hold for a minute, then ramp up to 80% hold for a minute, then release it to what ever it needs. Rarely runs at 100% and yes at 100 it is a tad noisy. Shut down it the reverse. I choose this because I wanted more humidity control. Works, every time the motor goes to 80% the condensate pump cycles pushing 2 quarts of water out.
4" filter? How did you fit that in the bottom of the air handler. Mine will not except anything other than a 1 inch thick filter.
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No. Sounds about the same. I easily can program the dip switches but wondering if adverse consequences to certain program settings. I know that 350 cfm/ton is option for humid areas for better dehumidification but wondering if any disadvantage to that setting in heat mode (such as possibly causing auxilliary heat to kick in at higher outside temp). I had a 5" Honeywell media air cleaner (similar to Trane "Perfect Fit" w/ media filter) installed with system to minimize air resistance/static pressure. Same case as Honeywell electronic but didn't want to deal w/ electronic cleaner (could fit one in later if decided to). Also, is there a setting to keep auxilliary resistance heat from kicking in until heat pump is unable to achieve or maintain temp on its own (i.e. lock out "toaster mode" above the balance point) or is it necessary to add an outside thermostat and guess at outside balance point temp setting?
Thanks.

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