Hay all, I need some help with system design. For the past 13 years I have been heating my house and producing domestic hot water with my outdoor wood boiler. My old boiler had a propane burner in it, so when I didn't want to burn wood (or ran out), I would switch to propane. The current G200 boiler does not have a propane system, so I have no backup. At all. I have no system in my house, such as a small propane boiler or electric water heater, that will provide me with hot water during the summer or even a backup in case of a major system failure or an extended vacation.
So, this spring I have saved up some money and I want to install a heat-pump hybrid electric water heater. I want it to serve two functions: First, to serve as primary domestic hot water from mid-April through early September. The OWB would be shut off completely. Second, to act as a backup if I have a system failure in the OWB, or I want to be away from my house for a few days in the winter and just need to maintain a minimum heat level. I want to be able to manually switch modes (if necessary) between seasons, and manually switch to backup in case of a failure or vacation. I have a generator to provide backup power so using electric backup is not a concern.
Currently, I have a 40-gallon indirect water tank, which is fed from the primary OWB loop in the basement, has its' own small circulator pump loop, and the hot water flows through a mixing valve to domestic use. The rest of the OWB loop is for heating. Compounding matters, the indirect tank has developed pinhole leaks and is out of warranty. I want to replace the indirect tank with the electric water heater. I do not have room for both, so I need the electric heater to function as an indirect tank during the winter months when the outdoor boiler is running, and function as primary heat for domestic hot water during the summer. I only need the electric heater to provide minimal heating if a backup is needed during the winter, and I would like to accomplish that with some sort of valved bypass.
So, does anyone have any photos of systems that utilize both an electric water heater and an outdoor wood boiler, or have some sketches, or barring that, describe to me what I need to do? I am on a very limited budget, and have some reasonable plumbing skills, so as long as I have an actual plan, I can put it together.