UGF Heating Alternative

> From: Bob Woolley <macaw at tiac_net>
> I was thinking about UGF and came up with the following: What about =
> putting a spaced coil of hard PVC tubing(say 1/8 inch diam) under =
> the substrate and pumping warm( or hot) water through it in a closed =
> loop system? Any thoughts on this??

Aside: Where in the heck do these "=" and extra spaces come from?
Even my normally pristine postings seem affected in the latest APD. 

Some thoughts about the above:

1. PVC is a relatively good insulator.  You would not get very
effective heat transfer from the tubing to the substrate. 

2. The gravel near the "hot" end of the coil would get more heat than
the gravel towards the outlet end of the coil as heat is slowly
dissipated.  Depending on how it was set up, you might be heating only
the first foot or so.

3. How hot does the water need to be to warm the gravel enough?  The
Dupla coils get to about 90 F.  If the PVC acts as insulation, how
much hotter does the water need to be?  And how will you get it that