I am designing a system to ensure that we have backup power for a high efficiency natural gas furnace (mainly-I will likely also include a receptacle to provide current elsewhere if needed). I plan on using a Victron Multiplus 24V2000A -50 inverter/charger with two 12V100Ah LiFePO4 batteries in parallel. I am looking at connecting the AC IN side of the inverter to my basement subpanel on 15A breaker, then the AC OUT to the furnace with an emergency shut off switch (required by code here) at the foot of my stairs. I think this part is fairly straight forward. But the Victron Wiring Unlimited book suggest adding a bypass so that - in the event I need to take out the inverter (or decide to feed the furnace directly from the panel) - the furnace can continue to be online. How is this done while making sure there is no possibility for backfeed? In particular what kind of switch is required and how is it tied into the circuit?