Hello all,

I'm in the Dallas, Tx area, and have to replace a 4 ton
system with a grounded compressor. The good news is that it's lasted for 22
years and been uncharacteristically cool so far this year; the bad news is that
it's going to get really hot here soon, and the unit conditioning the master
and one of the kid's rooms, so have to replace, like, NOW. I'm an engineer, so have
done a lot of research on this to become educated, but am NOT a professional
HVAC guy, so need your help

I'm getting quotes from several top contractors with very
good referrals/install processes and reputations, all doing Man J, so am
confident that the install will be excellent regardless of the equipment. Will
cover any equipment questions in another post as necessary - this one is about
my original builder duct work. My experience is that it’s like pulling teeth to
get the HVAC contractors around here to do their work on the ducts, but dang
it, I’m committed to make them face their fears ;)….

Our home is around 4600 sqft, with 3 zones. The one that is
out services the front part of the house. The Man J’s have confirmed that it
needs to be a 4 ton system, and will be updating the duct work as a part of it.
All duct is currently flex. The duct work and furnace sits in the attic (as
most in TX), and supplies a bedroom and bath directly below the furnace, then
the HUGE VOLUME (22 foot ceiling entry area open to the upstairs), then the
master bedroom, bath and closet 50+ feet away. The current builder-installed
system has 2 returns, a 14" outside the master bedroom, and an 8" at
the top of the entry area, but none in the master or front bedroom, so I know
that's not enough return. As a part of the upgrade, I'll be adding a 12"
return in the master for better air flow, but will leave the front bedroom
alone, as it's below an upstairs bedroom and would be nearly impossible to
access (it also gets GREAT airflow, as it sits under the furnace; not ideal,
but works fine;)) I "think" that should solve the lack of return
issues, but would welcome any input on this part.

NOW, to the part that has me most confused. The current
system has 8 supply registers. The front bedroom and bath each have their own
supply runs. The rest of the front of the house is served by a 14" inch
flex trunk that runs 50+ feet that drops 10 feet down from the front area into
the attic space over the master, where it is terminated into a duct board box
(yep even though it's an expensive custom house, this is a hack job)..... The
box then has flex branches that serve the rest of the front of the house. Two
ducts climb back up into the entry area (a 10 inch and a 9 inch), two in the
master bedroom (9 inch), one in the master bath (8 inch), and one to the master
closet (4 inch). I installed a high cfm remote air flow fan system in the
master bath when we remodeled it a while back to get rid of the moisture, but
the master bath, with its one supply (oh, forgot to mention, ALL rooms are high
ceilings - master is 12', master bath is 15') and south-facing window gets
pretty toasty when my wife is running her hair dryer and curling iron, even
with the fan off;). SO, am thinking of adding a second 8" supply to the
master bath. Opinions would be great here as well.

So after all of this, my MAIN question is about the
approaches of the various contractors in updating the supply side of the duct
work. They seem to be split between running multiple new supply ducts, splitting
them with metal "Y's", and running to/updating the duct box with
additional drops. My searches have not given me any definative guidance on
this. Some say that more "home runs" with "Y" adapters are
better, while others say that the "remote distribution box" reduces
static pressure and increases airflow. HELP!!!! When I quiz the contractors,
they all have pretty well reasoned replies; I just need the right ANSWER!! I'm
sure it's written somewhere in Man D, but I don't have access to, or time to
review it.

Sorry for the long post. Wish I had the time to do more
research/engage more contractors to evaluate, but it's about to get really hot
down here, so have to make a call with imperfect information. Any guidance that
you can provide will be VERY much appreciated, as I'm certain that I can get
the short list of companies I'm working with to implement the solution that I
specify, if I'm able to do so. THANKS IN ADVANCE!!