Cindy Hamilton wrote:
...and that water in the return line never gets hot? ...or it never
cools off? You're FOS

Well, look at it this way:

The water in the return line is probably close to room temperature.
He only
has to heat it from room temperature to his target temperature. If
he was pulling in cold water from underground, his heater would have a
lot more work to do. Yes, there are losses when he's done using hot
water, but probably not as great as the usage from heating up all of
that
40 F water.

Very good point. I hadn't even thought of that aspect. It probably doubles the
savings I get.

It is nice to see others here that can really think.