Hoverfly, if the appliance draws 400 watts then to run it you would need at least a 400 watt generator. No multiplication by 60 required.
The thing that gets most folks is the well pump (if you have one). Typically they are 220V and 2-3hp, so they are the biggest load you would need to drive. You also need to have 220V output from the generator. Without water, life sucks and you can't get the most basic things done. If you are on city water, and use sensible lights (cfl's) the 2kW Honda EU generator is perfect. It has an inverter system and the motor speed is dependent on the load (regular gen set runs at 3600 rpm all the time). If you have a low load, it runs slower quieter and saves fuel and wear. More load, it runs faster to match.
The biggest limitation on generator life is the oil change interval. Many require the oil changed every 15-20 hours, which would be once a day in 24/7 operation. The better generators take more oil, have a pressure lubrication system with a spin on filter and the best are water cooled so that the oil does not have such a hard life.
Hoverfly said:
Take the maximum watts a pellet stove will use, for instance my Mini will use a total 400 watts for lighting, there for 400 X 60 = 2400 watts. If you don't use the igniter and just start it withe some starter fluid then the Mini will use around 200 watts there for 200 X 60 = 1200 watts. If you are with in the continuous rating of the generator not the surge rating then you can run it with the generator.