What size generator do you actually need? The wattage worksheet

Most generator mistakes happen at the point of sale, not in the service bay: people buy big (wasteful fuel, abusive noise) or small (an overload every time the fridge kicks in). The fix is ten minutes of arithmetic before you shop - and one concept: running watts versus starting surge.

The one concept that settles everything

Every appliance has a running wattage - what it draws while working - and some have a starting surge, a brief spike two to three times higher when motors kick in. Fridges, freezers, pumps, fans, air conditioners and anything else with a compressor or motor surge; lights, TVs, laptops and phone chargers barely do. Your generator must carry everything running plus the single largest surge likely to start - not the sum of all surges, which almost never start at once.

The worksheet

List what must run during an outage, honestly. Typical rough figures to plan with - the nameplate sticker on each appliance wins ties: fridge: 150-300 W running, surging toward 600-1,000; chest freezer: similar; half-HP water pump: 750-1,100 W running with a hard surge; 1.5 hp AC: 1,100-1,600 W running with a surge well beyond that - the item that changes the whole plan; standing fan: 60-90 W each; TV + decoder: 100-200 W; laptops, lights, router: 150-250 W all together. Add your running column, add the largest surge on top, and buy the next size up - roughly: 1.5-2 kVA carries lights, fans, TV and the fridge; 2.5-3.5 kVA adds the pump; anything feeding an AC starts at 3.5-5 kVA and honesty about fuel bills.

Load-shedding beats size

The cheapest upgrade is a plan, not kVA: decide the outage hierarchy before it happens (fridge and one light bay first, luxury appliances queue behind) and label the changeover switch accordingly. A generator running at 30 per cent load wastes fuel and carbon-fouls itself; one at 90 per cent lives on a cliff edge every time the compressor kicks. See generator versus inverter for where a battery inverter should cover the small loads, changeover switch care for the wiring side, and outlet overloading for the fires this whole exercise prevents.

The rules that are not negotiable

Generators run outside, several metres from windows and doors - exhaust carbon monoxide kills quietly indoors and on balconies (the alarms exist for this: how many alarms and where). Refuel only after a cool-down - the cap-off-a-hot-generator fire is a classic (fuel storage itself has rules: jerrycan safety). And anything wired into the house circuits belongs to a licensed electrician - the generator stays a plug-in appliance until a professional says otherwise (the wiring red flags tell you why).

General information, not professional advice. Nameplate figures beat every number on this page; the electrician beats both.