Re: under gravel heating cables -- Hypotheses vs Evidence

["S. Hieber" <shieber at yahoo_com>]

James Purchase presented some very good questions about
heating cables and suggested some further evidence that
could help one decide if they really help plants (or how
much).  The hypotheses about their function are relatively
well known, but he evidence is less prevalent.

I'd like to add that not all heating cable setups are equal
and some might be beneficial and others ineffective.  Some
folks are in favor of relatively higher heat cables and
other (e.g., Dennerle) lower heat.  It could be that one
way has some benefits for plants and not the other.

I don't recall anyone ever saying that cables *don't* have
benefits for plants.  More often the comment is something
like I didn't see a difference -- which could mean (or
indicate) that the benefits are small and overshadowed by
other factors, which have greater impact.

The basic idea is that the heat differentials cause water
currents that move things in and out of the substrate. 
Well, in a well planted tank, the roots do that, too.  So I
think the question is how much better does it get with
cables and under what conditions, than what the roots
already do?

Anyway you slice it, cable heater setups usually cost more
to purchase than decent tube heaters.  However, I suspect
you might earn the purchase cost difference back over a few
(many?) years in electricity savings. 

Scott H.

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