Here's a diagram of the system I designed for my house. I had an extra water heater tank outside in a small pump house for a spa so I tied it into the system for extra storage capacity. I run the system at about 25 psi normally which is still fine for taking showers and running inside. An y-strainer makes sure nothing gets into the recirculation pump.
Figuring that a boiler is a boiler and I needed a backup plan for cloudy days, I built a little fire box out of cinder block topped with steel and made a bio-mass (wood) heater system that could be the first step of my plumbing reaching out to my CSP trough collector. Anyway, I've got a 20' coil of 3/8" OD copper tubing wound in a double coil with the first half wrapped around some 2" tubing and the second half wrapped around some 4" diameter pipe so that the inlet and outlets end up being on the same end, and the coils are evenly spaced for good heat exchange. I've measured temperature differentials of around 65 degrees at flow rate of about 1.5 quarts per minute.
A controller that measures the tank temperature and the outflow temperature is very important in this application. A T-Diff controller can sound an alarm and also regulate pump operation more efficiently. I designed my system so that everything could be drained to prevent freeze damage, but a T-Diff controller could also activate the pump to circulate warmer water to prevent freezing. Another component I incorporated that's absent from this diagram is a flow sensor which is very important to monitor incorrect valve settings or issues with pump power.