There is no "not enough hot water usage" to justify a single tank setup. Either you use enough hot water, and you should go with 2 tank, or you have so little water usage, that you can skip the desuperheater at all and use a point of use or on demand electric. I re-read your thread and looked at the performance numbers. A 4 ton system with St. Louis MO weather data and your loads actually runs cheaper then a 5 ton system despite going slightly more into aux, because the 4 ton heatpumps run more efficient (better COP) than the 5 tons. You know what I would do: Call up the guy you liked most, assuming the references checked out, and tell them that you liked them most, but that he was much more expensive, and that you did not like him $4000 more. Ask him if he is willing to come down and match the others quote, and you have a deal. If he does not, go with the other guys. Simple. However, not matter what you do, insist on a 2 tank setup if you feel it is worth it with a DSH. Temperature and Energy logging by: Web Energy Logger Temperature and Energy logging by: Web Energy Logger Here are 2 system streaming data with "2 older folks household". As you can see, 3 ton systems, and not a single time in the last 24 hours was the DSH not contributing to the hot water generation while the system was running.