I think this will work for now. I have the big tank at 120 degrees or so. Since the big tank feeds the little tank, I can only make a good guess based on the dial. (normally, I measure the water temp. with a small thermometer) I have the thermostat on the little tank at 123 degrees. The interesting thing about the little tank thermo is the trip-on setting. I am not 100% sure but I think it has a -7 setpoint trigger. That means the element turns on at 116 degrees. This means that the little tank will not turn on unless the water has sat for some time or the incoming water drops below the trip-on point. So the little tank is a buffer.

After a week with this setup I have about the same heat pump energy usage and a much improved little tank usage of about 1kW a day. It is better for me to use hot water throughout the day. (no need to wash hands is cold water) Why? because the big tanks outgoing water will help keep the little tank from turning on.

What does the wife think? She just want hot water when she wants it. i.e. don’t mess with my hot water!