I'd like to implement a backup water heater without creating a "hydrostatic pipe bomb" or violating any meaningful plumbing code requirements.
My thought is to connect both water heaters to the cold water supply with a single ball valve in line with each inlet connection. The outlets would be connected through 3-way valves configured so that each water heater is either connected to the house hot water line or open to a drain.
I've though of using ball valves on the inlet and outlet ports and installing redundant pressure relief valves so that if the TPE valve failed there'd be backup but think the 3-way valves are safer.
One of these water heaters is a 450,000 btu/hr oil fired unit and the backup unit will be a 9 kw electric unit.
I'm in an area with no plumbing permitting or code enforcement but that doesn't mean I have a death wish. Getting a replacement unit in can take several weeks when the weather is bad so I'd like to be able to just switch over in the event of a failure.
Comments on code violations?
Thanks, RB