Went back and checked installation instructions for my geothermal system. It clearly states two H2O’s with one being the “pre-heat” tank and the note states “Do not connect electrical to pre-heat tank.” It says to use two 52 gallon units (That’s what I have, not 42 gal. as I erroneously stated earlier). The manual also states that if only one H2O is used a 52 gal is for four person households and an 80 gal for more than four. It also states that where it is necessary to use only one H2O the thermostat should be set to not greater than 100 degrees. Setting higher will result in the heat exchanger working in reverse and possibly causing damage to the geo unit.
In this case the homeowner will be unhappy as the H2O output temp will be low and if the temp is increased the geo will not maintain the high efficiency associated with the units.
I wonder if you can guess who will get the blame for any unit/H2O problems?