A: PrestoneAntifreeze, If by "owner" you are referring to the primary hot water unit, this will be fine. We refer to this as a booster application. You will simply run the primary hot water unit's Hot line into the ES4's Cold intake.
A: John, Yes, that is a common application. Just run your Hot line from your primary hot water source into the Cold intake of this unit and then run the Hot line from this unit to your shower. Place this unit as close to your shower as possible to reduce any lag time.
A: No, this is not how a radiant floor system works. Mike