blueman wrote:
" writes:

solid lines are smooth inside with less air turblance so theres better
airflow, in addition regular lines are harder to damage

I know what you say is certainly true from physics -- turbulence is
wasted energy and disrupts smooth laminar flow etc.

But do you know how big a factor that is?
I'm actually interested because the incompetent "pro" who installed the
system for the previous owner ran flex duct all over the place and we
are trying to decide whether it pays to replace.

Friction factors from Bill Pentz's site
(http://billpentz.com/woodworking/cyc...tingResistance)

Higher numbers are better:

1. Corrugated steel duct= 60
2. Spiral Duct = 90-100
3. Laser Welded Steel Duct = 110-125
4. PVC Duct = 146

In other places, flex hose is taken to have roughly 3X the resistance of
smooth ducting of the same size.

Chris