This has been an invaluable resource to me as I recently completed my geothermal retrofit; thank you to everyone and I hope I can contribute some useful knowledge. I have browsed the forum for some answers to my final question, which is what temperature should I set my hot water buffer thank to? The one that is connected to the desuper heater on my 5 series WaterFurnace. Previous owner of the house installed 2x 80gal electric hot water heaters in series. He had no interest in energy efficiency Oddly enough, the first one in series (cold water in) was set to a higher temp (130F) than the supply hot water to the house (120F). The desuper is now hooked up to the first one in series, and the lowest temp on the hot water thermostat is 120F. I've set the supply tank to 130F because my wife was complaining our water wasn't hot enough. I understand the thermodynamics involved with desuper heaters, and am not questioning the rationale of buffer tanks. Based on thermodynamics, it seems I'd actually want my buffer tank off entirely, but then I started reading about bacteria growth in hot water heaters between 100-120F, the outflow temp from the desuper. However that temp also reduces the efficiency of the desuper because it can't dump the heat, but could in fact pull heat from the water. So what is the ideal set point? Can I turn it off? Minimum temp of 110-120? Apologies if I've missed the answer somewhere on the forum!