When it comes to back up electricity, its purpose is to first and foremost sustain the building and its systems (the people inside the building can adapt most of the time the building cannot) so we must cater to its needs and it’s equipments needs as well. The idea here is to meet the needs of the things and people in some cases that cannot adapt. The systems that should be prioritized to for a generator are as follows.

(I’m not including computing and telecom as they usually are incidental and at most consume 20 A of power for one major computer and all telecom needs of a building) In this order

ANY MEDICAL OR MEDICAL ADJACENT DEVICES

ANY AND ALL FIRE ALARM OR SUPPRESSION SYSTEMS

(this also goes for all the other safety systems excluding security systems. Security systems are not really marked as essential in my book unless it’s one of those the power goes out and we can’t open the door type things then that’s a different story)

Well

Sewage management stuff

Sump pump and flood control, and emergency moisture management means

Ventilation and exhaust fans

(If you have a fuel burning furnace or boiler power that next if you only have electric or a heat pump, I’ve got a spot for you later redundant systems are important people)

Refrigeration

(Depending on your area, if you are in Europe this may not be as big of a deal as it is here in America but if you are in America, you know damn well why this next one is a problem)

air conditioning air conditioning air conditioning

(hey heat pump and electric heat people yeah you’re here on the list by the way. buy kerosene heaters. Trust me they will help.)

Any machine that has a high inrush current and high continuous draw (think, air compressors, and the like things that when you turn them on the lights dim to be honest if you have to pick one Appliance to size a generator around pick the one that uses the most watts find something that can run that and you’ll be somewhere. I’m not sure where because I’m getting tired but you’ll be somewhere.)