I'm looking for a few opinions (I know, there are LOTS of opinions
here).


Over the last few years, I've been evaluating replacing an existing
Carrier AC system in my home. The existing unit was built in 1987 and
has been working fine, though I suspect it's days are numbered. Hence
I've been comparing options.


Based on my own rough Manual J, as well as estimates of a couple
contractors that have been out here, the house should have about a 4
ton unit. Currently it's running with a 5 ton unit (the previous owner
always liked to supersize everything...) so I'm stuck with a system
that doesn't effectively remove moisture or maintain a stable
temperature. So I'm looking at making some changes.


Today I had a guy in who strongly pushed a Unico high velocity system
- tear out all the existing ductwork and replace the entire system. I
hadn't considered this previously because, well, it seemed like
overkill. But I'm comparing all options. So that's option 1.


A second option is to replace the existing units with a nice variable
speed air handler and two stage compressor, keeping the existing
ductwork. That's appealing as it should be quite efficient and
maintains the investment in ductwork (which the contractors have told
me was quality work).


The third option is to do option 2 and add another zone. This would
require some additional ductwork but the guys I've talked to said that
the current ducting is set up pretty well for this addition.


Here are my specific questions:
1) I've heard that the HV systems can be noisy and inefficient. This
makes intuitive sense since the HV systems will require more energy to
push air around. Smaller tubes = greater resistance. Plus, higher
velocity would imply higher turbulence and hence more noise, though
I've heard this is offset for by lower overall CFM.


2) I've heard that HV systems can be considerably more pricey. I'm
waiting on the proposal, but from what I've heard, $10-20k is in the
ballpark. Is it a rule that HV systems are considerably more expensive
than a modern, 15 SEER dual stage, variable speed system? Or are
people comparing them to run of the mill systems? For reference, last
year I had a quote of $6600 for the retrofit including a Carrier
38TDB048-3 and FV4BNB006000 (with all labor etc.) which seems like a
pretty decent price.


3) While the air flow isn't optimal and I think a two zone system is
warrented for maximum comfort, is there any reason why I shouldn't go
for the simple upgrade, see how it feels next year, then add the
second zone if necessary a few years down the line? I've lived with
the current non-optimal setup for 5 summers so far and it really
hasn't been such a big problem. I understand that it will cost more if
I do it in two shots, but are there any other fundamental reasons why
I shouldn't go this route?


Thanks for the feedback.
-Ted