Repairman calls me telling me that the stove works, the issue is that the tenant didn't know there was a preheat time difference between gas stoves (what she's used to), and electric stoves (the previous and new stove in the unit).

Around Jan/Feb 2014 my husband and I had credit scores that looked more like what you preheat your oven on to cook a pizza or broil some chicken.  

You do it by hooking two in series, the first turned low pre-heating the water to the 2nd, with the 2nd being a fast recovery unit.

Our experience has been they struggle with the lift required for winter water temperatures in northern climates.On the other hand, they work find behind a solar thermal storage system which will pre-heat the water, leaving the electric on-demand to handle the final boost of water temperature en-route to a given unit.

Rather than install a geothermal heat pump(s), it may be cheaper to separate the units and install four smaller {gas} boilers - with perhaps a solar thermal array to preheat the return water and to supply domestic hot water - particularly during the warmer season so you do not need to fire the boiler.

We're starting to gain traction on the furnished rental front.I've got one in the kitchen right now (pre-heating the oven atm), not in the Bay Area but down in SoCal right on the beach, where it's a portfolio Jumbo loan predicated mostly on AirBnB income and very little day-job income, on an exception basis with strong reserves and solid credit. 

Preheat the oven and mix the ingredients. 

In my last apartment we had a brand new, never been used oven and we would preheat the oven, open the door to put food in and the smoke detector would go off! 

In the one with a steam boiler, I have the supply running through an exchanger in the boiler to preheat the water so as not to get slow tank recovery when the supply water is in the low 40s.

Consider tankless heaters for each unit so that they can use the solar array as a preheater but also heat as needed.