Though this is not a solar or really a geothermal application I thought I might get a better quality of answer on that forum than on the water heater forum, but I'll give this a shot.
I live in the Salt Lake City area and am a retired HVACR contractor – now a university professor :-) . About 30 years ago I installed an ECU “Energy Conservation Unit” (actually a superheat recovery system) on my split system AC. Is use my 50 gal NG fired tank water heater as the heat sink and have enjoyed both reduced compressor head pressure (lower power bills) and some level of free hot water during the AC season for a number of years now. About three years ago I installed a 200,000 BTU direct vent Takagi tankless water heater in back (on the use side) of the tank and turned the tank temp down to about 55 to 65 degrees - but even in mid-winter it rarely fires. This means that the tank is serving both as a tempering tank and as a heat sink for the ECU in the AC season. During the summer the tankless rarely fires when hot water is demanded since the ECU is preheating the tank water to 130 to 140 degrees. I also get a good flow during the winter months when the water supplied to the house is between 40 and 45 degrees. The mechanical room is inside the house and once I upgrade the two furnaces in the mechanical room to high efficiency direct vent units I will disconnect the gas supply and B-Vent from the storage tank and the open louvered outside air supply to the room will be closed.
I would like to finish a hot water recirculation system I started two years ago to reduce the wasted water while waiting for the hot water to reach the point of use. I have two return loops of 3/8" insulated PEX roughed in. The loops are both about 35’ in length. These return loops would ultimately feed either into the “old” tank water heater fill pipe or into the bottom drain of the tank. Of course the system will have the appropriate expansion tank and checkvalves. I am not interested in cold water return loop systems.
All of this now said what pump manufacturer and model would anyone recommend?