The pool our PB is about to start is 40" by 12". On the shallow end (4' depth) is a 7 x 7 Spa in one side/corner and the width that remains on the other side is a Baja Bench. My wife and I have seen spas configured like ours (inside the pool, in the corner) where the tops of the two walls for the Spa are what appears to be about an inch under the water. We really like this look as the entire surface of the pool is not interrupted by the protruding walls of the Spa.

Our PB is telling us that he thinks we will have a hard time heating the Spa. My question is: How inefficient would this configuration be? Will it take take double the energy to heat the Spa? I'm thinking that since the water out-take is on bottom and the jets are up higher that the Spa when running should not really sucking water from the pool.

Thoughts? Any other concerns with this configuration?

Thanks, Jim