What size generator do I need?

A typical fridge runs on about 200 W but needs about 1,200 W for a second or two when its compressor starts. On its own, that means a generator label showing at least 300 W running and 1,200 W starting. Add a freezer, LED lights, Wi-Fi and a phone charger and it comes to 485 W running and 1,485 W at peak: at least 700 W running and 1,500 W starting. Check the starting number on the label, because some small generators start less than that. Older fridges can need more to start.

It depends on what you run at the same time, not on the size of the house. Outage essentials (fridge, freezer, LED lights, Wi-Fi, phone charging, a CPAP and a sump pump) come to 1,345 W running and 2,345 W at peak: at least 1,700 W running and 2,400 W starting. Add a furnace fan, a well pump and a microwave and it’s 3,945 W running and 5,045 W at peak: at least 5,000 W running and 5,100 W starting. Central air, an electric range, a dryer or an electric water heater can push you past the biggest common portables, which run about 12,000 to 16,000 W. That is home standby size, so have a licensed electrician size and install it.

A 30 amp RV hookup can deliver up to 3,600 W (30 amps × 120 volts). Most 30 amp rigs have one air conditioner, and its start is the hard part: about 1,600 W running but about 3,500 W to start. The AC plus LED lights, a TV, a laptop and a phone charger comes to 1,870 W running and 3,770 W at peak: at least 2,400 W running and 3,800 W starting. Many “2,000 W” inverters start at about 2,000 W, so one alone won’t start that AC. A soft start fitted to the AC lowers its starting kick. If you have one, add the AC as your own item with its new numbers.

Count only what runs at the same time. Typical outage essentials: a fridge about 200 W, a freezer 180 W, LED lights 80 W, Wi-Fi 15 W, phone charging 10 W, a CPAP 60 W and a sump pump 800 W. That is 1,345 W running. Then add the single biggest starting kick, here the fridge at 1,000 W extra, for a 2,345 W peak. Start the biggest motor first, then switch the rest on one at a time.

A typical sump pump runs on about 800 W and needs about 1,300 W to start: at least 1,000 W running and 1,300 W starting. A typical well pump runs on about 1,000 W and needs about 2,100 W to start: at least 1,300 W running and 2,100 W starting. Both together need at least 2,300 W running and 2,900 W starting. Pumps vary, and older ones can need more to start, so check the label. Many well pumps run on 240 volts and are hardwired, which means a generator with a 240 V outlet and a transfer switch or interlock installed by an electrician.

Runtime is capacity × about 85% ÷ load. A 1,024 Wh power station runs a 60 W CPAP for about 14 h 30 min, or a fridge drawing 200 W nonstop for about 4 h 20 min. Fridges cycle on and off, so real runtime is usually longer. Turning off a CPAP’s heated humidifier usually stretches runtime a lot. The station must also handle the start: a fridge needs about 1,200 W for a moment, so check its surge rating.

Starting kicks last a second or two, and motors rarely start at the exact same moment. Adding every kick would size for a moment that rarely happens. The catch: two motors can occasionally start together, like a fridge and a sump pump. If your generator trips when that happens, give yourself more starting headroom, or stagger what you can.