I inspected an 11,000+ square foot house yesterday that had a water heater setup that I had not encountered before. It had a pair of 199,900 BTU/hr tankless units installed conventionally on one area of the house, but the other installation paired a similar tankless unit with a 6 gallon 120v electric tank type unit with a circulating pump. The electric water heater was plugged into power.
What would be the rationale for supplying power to the electric water heater or even having it in this configuration? Does the rate of flow from the circulating pump not activate the flow switch on the tankless unit unless there is demand? I’ve seen tankless systems with circulating pumps, but not combined with a live electric tank unit.