Tankless Water Heater on Oil Burner

solarguyDC

I have a tankless hot water heater on my oil boiler.  I have recently installed new mini splits throughout the house that I use for my heat and air conditioning.  I am trying to convert my domestic hot water over to an electric hot water heater but I want to keep the existing (working) boiler and hydronic radiators throughout the house as emergency heat if the power goes out.  I am a solar guy so I am 100% energy independent and have enough battery storage to run off the grid for about 4-5 days.  That being said I have a full tank of oil and frankly there is nothing wrong with the boiler I just don’t ant to bypass the tankless hot water heater and direct it to an electric one.  If the power goes out for an extended period of time I can redirect the domestic water back through the boiler and get hot water that way until the power/sun comes back.  Any suggestions on how to achieve this if possible. 

hot_rod

A manual system where you need to turn valves?
Or an automatic system that monitors temperature and makes the decision.

Solar delta T controllers can make the decision, a 3 way motorized valve does the switch, for an automatic system. I have a bunch of 12 and 24VDC controllers if you want to use your battery to run the control.

pecmsg

Yes it can be done. A little creative piping is needed. 

Heat pumps are nice and have come a long way. Do you know the batteries have the capacity to start the heat pumps? 

You're probably capable of starting the HPWH, they’re a small compressor.