On Thu, 23 May 2013 06:25:24 -0700 (PDT), "
wrote:

Yes, it will be on for less time, but it will also be
using proportionately more electricity than the smaller
unit while it's running. There isn't a free lunch here.
The real advantage of the larger one is that it will heat
the pool faster

All true. However, based on the OP's posted numbers, the larger unit
is slightly more efficient, roughly 6% more efficient. But that
doesn't change what you say -- running for less time isn't a savings
in and of itself.

Edward