What guidelines are there for ducting replacement along with a new
residential HVAC system? This is a small (1300 sq ft) home in Southern
California that's about 30 years old. It has the original HVAC system and
all the attic ducting is original as well. The ducting appears to be made
of the same flexible, corrogated aluminum that the dryer uses, but larger
and wrapped in about 2 inches of fiberglass insulation. There are no
obvious leaks or gaps, but the AC system does not seem very efficient (duh,
30 years old), so I might be losing some of my heating.cooling that way.

The installer strongly suggests replacement, and common sense says this
probably a good idea, but this would add a considerable amount to the total
system cost. I definitely don't want to do it myself.

What are the appropriate materals, etc. for a modern residential attic duct
system, and can anyone make a guess at a reasonable cost for reducting the
house? (All of it is in the attic, and there is good access to everything
up there. There are eight vents in the house, and the heater assembly is in
the middle area of the house. Pretty typical stuff, I would guess.)

Gratitude in advance for any advice.

- Magnusfarce