Where the loops are placed will result in different characteristics of the system, such as how quickly it heats up and cools down. Having the tubes placed in the slab makes the most use of the thermal mass of the slab but with slower response times. Even placement within the slab has an effect on response time, as does the thickness of the slab. It all depends what you want to achieve.

Have you considered doing this with geothermal?

SR

I have not considered Geothermal. The system is in Santa Barbara, average temp 60 degrees. I assumed Geothermals costs/benefits come in colder climates.

Any idea which is the ideal choice in the slab or using Warm Boards or similar?

If you were looking for a quick heating response probably Warm Boards would be the way to go. Speak with installers that have experience in your climate.

Are you planning to install A/C, a heated pool or hot tub? A single multi-purpose geothermal unit can have many uses transferring heat energy from one place where it's not needed to another where it is at almost twice the efficiency of single a purpose geothermal unit.

Geothermal is used in all climates, you could look into it, or not.

SR