We are still in the process of renovating our condo's kitchen, including replacing our old electric tank water heater (we have no gas lines in our complex). After looking for reviews, and not finding much on the web, of the Heatworks tankless water heaters, I took a risk and purchased two Model 1 units through my kitchen renovation contractor. My contractor's electrician and plumber installed and connected the units in parallel, as suggested by the Heatworks User’s Manual, inside a new kitchen cabinet, to operate as a whole-house system. The Manual recommends to connect 18" of flex tubing to the unit's inlet and outlet ports before using PEX. The plumber used a combination of flex tubing and copper to make those connections.
Within two weeks after putting them into operation, one unit began to leak around the outside of the inlet port. After I called Heatworks directly for assistance, the company sent me another unit to replace (at my expense) the leaker. Less than a week after the replacement unit was installed, the other original unit uncontrollably heated water overnight (with no water running at the time, mind you) to the point that the hot water in the PEX tubing exceeded the PEX rating. This resulted in the PEX bursting, and water pouring out of the cabinet while we slept. I woke up to the sound of rushing water downstairs, two inches of water on the entire first floor of our home, and countless gallons more flowing down the street from our condo and into the gutter. The copper and flex tube connected to the unit outlet were scalding hot, well above the 115-degree setting my contractor programmed into the unit. The water damaged our brand new kitchen cabinets and tile flooring, as well as our hardwood flooring in the rest of the downstairs. Now we face more headaches to repair all the damage. Needless to say, the failure of both units in a month after installation has convinced us to go with a different solution to our needs.
So if you're thinking of going with an electric tankless water heater system in your home improvement project, just be aware of what happened to me.