Does anyone have a failproof way to size generators correctly? I have been told a number of different ways that don't seem logical or would take way to long. Can anyone help me out?
Why don't you provide some more detail about what approach was suggested and what doesn't make sense?
As far as a practical approach, I usually provide the load, operating time and requirements etc. to manufacturing reps and let the generator company recommend the sizing.
The most straight forward way is using the various manufacturer sizing programs. You can input all your various loads (includes nuances for special loads like fire pumps), also if you want to step the loads incrementaly to reduce the genset size.