I have read much about the superiority of indirect-fired DHW systems over tankless coils. I am surprised to find little about using a standard electric water heater as a storage device (read MUCH CHEAPER) and a small bronze circulating pump to circulate potable water through a boiler’s tankless coil. Doesn’t this accomplish the same thing for less money up front? I admit to increasing my investment by purchasing a State plastic water heater with R-25 insulation, but this did not approach the cost of most indirect tanks.
The lower thermostat is used as a switch to turn on the pump when the tank calls for heat. A homemade coaxial fitting on the hot water discharge takes care of the third piping connection.
Another advantage is when the pump is running, any incoming cold water is preheated through the tankless coil, giving a shorter recovery time. The system can be shut down in the summer and converted back to conventional electric if you don’t want to fire the boiler.