UGH and reptile heaters

> From: "alan van nevel" <frog at theory_physics.missouri.edu>
> Date: Wed, 5 Jun 1996 09:23:07 -0500
> My 55 is on a stand where I can easily place a reptile heater on the
> bottom glass, which would definitely provide a slow flow through the
> substrate.

Don't be mislead into thinking that *any* amount of heat will produce
convection currents in the substrate.  Below a certain heat density,
heating is provided by CONDUCTION and will not produce a water flow. 
With low temperature differentials, the substrate and water in it will
act just like a solid with no movement.  You will still benefit from
having a warm(er) substrate but you will not achieve the full benefit
of convection currents. 

Unfortunately, exactly how much heat is required is not known and the 
calculations or modeling needed to determine that is a very difficult 

> I am just wondering what sort of temperatures the UGH maintains on the
> bottom.  

One of my Dupla setups provides a 10 degree F differential. 

> Anyone have an opinion if this is a workable idea.  I just can get a
> reptile heat tape really cheap.  An actual UGH would cost me more.

Give it a shot, you never know.  Some warmth will help a little.