If a person will start the generator and throw a switch or slide an interlock, you are in manual territory. If the generator must start and transfer on its own — for a sump pump, medical equipment, or an unoccupied house — you need a standby generator and an automatic transfer switch. An ATS is not something you add to a bargain portable unit and expect a whole-house automatic system.
r/Generator “explain it like I’m 5” threads lay this out as the main fork: portable + manual transfer or interlock, versus standby + ATS, with a large cost and fuel-connection difference. Manual equipment still has to be listed and permitted, and someone still has to be able to start the generator in the dark and keep loads within its running and starting watts.
An interlock is a manual method, not a third kind of automation. If limited dexterity or travel is the reason you want backup, do not talk yourself into a manual setup. Size the generator with the calculator.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.