Connecting a tankless water heater and separate hot water heater
What I have is this. An oil fired boiler that generates hot water for my house baseboard heating system. Contained within the boiler is a tankless heater that is heated by way of the firebox in the boiler. The tankless heater is used only for domestic hot water. It has a separate CW supply to the heater and is not in any way connected to the house baseboard heating system. The hot water exits the tankless heater and into a mixing valve and thence to the house plumbing fixtures. This is the only hot water source for the house and therefore the boiler has to run 365 days/year. I would like to install a NEW electric hot water heater and pipe it into the existing cold water supply and the existing domestic hot water to provide hot water during the summer months and turn off the boiler, thereby avoiding the $800.00 fuel oil bill that I incurr for the summer. I can pipe the EWH into the existing system with values to bypass the boiler tankless heater. What I need help in doing is how to pipe the system and still use the boiler tankless heater as well as the EWH during the winter months. I invision a HW pipe from the tankless heater into the CW supply of the EWH. Would I need a check valve to prevent HW from back feeding into the CW system? Your help in resolving this situation would be appreciated.
mtetter