fan location for solar collector

   I have 200 SF (25' * 8') of pass through solar collector on my south
facing wall. I've made some changes to my home and need to redo the
ducting on the collector. Pass through collectors run the air through a
felt absorber. There's a lot of head loss there, but there is also a lot
of square feet.

Basic idea here:
http://www.builditsolar.com/Projects/SpaceHeating/Kreamer%20Air%20Collector.pdf

The way I have this set up is with a center "fed" 8" * 15" plenum
running the 25' width of the collector (750 CFM or so...). The connector
is at the bottom and needs to make a turn before entering the house
below the sill.

I had this running with the plenum on the pressure (fan outlet) side.
What I wish to do is rewire this so the plenum would be on the suction
side. This way I can draw hot air from the collector and distribute it
inside the house through some no longer used wall vents (once part of a
converted gravity fed coal burning furnace).

So the question is where to put the fan. On the plenum and use it make
the turn, or downstream? Upstream might be 20' of 14" flex Y'd into a
couple of short 10" lines. The fan could be spliced anywhere in the 14"
line.

Is all insulated flex of the same R value about the same quality? The
big boxes carry Atco, Standex and Master Flow.

I'm obviously fishing for some ideas, and know that posting here with an
oddball question can give varied responses.  But such it is.

j