I believe the 2 vents connecting to the outside are 6" vents. However, on the interior, I want to connect 2 exhaust registers upstairs and 1or2 inlets downstairs. Do I need to halve the volume size upstairs to something like 4" pipe or can I simply just use a wye and use 6" everywhere? Also, what if one vent is longer do you need to balance that airflow somehow? Say from the wye it's 5' to one exhaust and 15' to the other exhaust.