We just put in a new oil burner/boiler with tankless hot water too. That was (insert choice word here) expensive!
In terms of hot water, you will typically have either 1/4 or 1/2 pipe going to/from your water heater. The cold water lines are usually 1/2. This is the same size pipe that typically runs to all your taps. There's really only enough hot water being produced to run one tap full out unless you have an odd piping situation.
Dave, if you're some place where the power goes out regularly, you can get a fail-over generator installed for about $5K that will power critical things like the well, heating unit, fridge, etc.
