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The right size depends on what you want to run at the same time. As a rough guide: 2,000 to 3,000 watts for camping, a fridge and lights, 3,500 to 5,000 watts for basic home essentials or an RV air conditioner, 5,000 to 7,500 watts for most home essentials including a sump or well pump, and 8,000 to 10,000+ watts if you want a window or small central AC on top.
Size bands at a glance
| Running watts | Typical use |
|---|---|
| 1,000–2,200 | Camping, tailgating, phones, lights, a fridge on its own |
| 2,800–3,500 | One RV air conditioner (often with a soft starter), fridge plus small loads |
| 4,000–6,000 | Fridge, freezer, furnace blower, sump pump, lights. Big loads one at a time. |
| 6,500–8,000 | Most home essentials including a well pump, through a transfer switch |
| 9,000–12,000+ | Essentials plus a window or small central AC, or an electric water heater on its own |
Work out your number
- List everything that might run at the same time.
- Find each item’s running watts on its data plate, or use typical values from the wattage calculator.
- Add the running watts.
- Find the largest extra starting surge, usually the fridge, a pump or an AC, and add it once.
- Add 10 to 20 percent headroom and compare with the generator’s running rating.
Example: a typical household list
Fridge (700 running / 2,200 starting), sump pump (1,050 / 2,150), furnace blower (700 / 1,400), lights and electronics (600), internet and phone charging (100). Running total: 3,150 watts. Add the largest extra surge, the fridge’s 1,500 watts, for a peak of 4,650 watts. With 15 percent headroom on running watts, a generator rated around 4,000 running watts and 5,000 or more starting watts fits. A 5,000 to 6,000 running watt model leaves room for a microwave or space heater in short bursts.
What to look for besides watts
- 240 volt needs. Well pumps and some furnaces need a 240 volt outlet (L14-30 or larger) and a transfer switch.
- Noise. Inverters are much quieter, which matters at campsites and in close neighborhoods.
- Fuel. Dual-fuel models run on propane, which stores for years without going stale. Output is usually a bit lower on propane.
- Weight. 7,500 watt models often weigh around 180 to 200 pounds. Wheels and handles matter.
- Altitude and heat reduce output. Check the manual’s derating guidance.
If it also has to go camping
One generator rarely suits both jobs perfectly. A 3,500 to 4,500 watt inverter with an RV outlet is a reasonable compromise. It runs an RV air conditioner and home essentials (without a well pump). Many people buy a small inverter for camping and a larger conventional or open-frame unit for home backup.
Before you buy: a final check
- Running watts cover your list with headroom.
- Starting watts cover the biggest motor.
- Outlets match your needs: L14-30 for a transfer switch, TT-30 for an RV.
- CO shutoff, low-oil shutdown and GFCI outlets.
- Electric start if anyone in the household can’t pull a recoil starter.
- You can move it, and store it safely.
And two sizing errors to steer clear of when you compare models:
- Sizing from the starting watts printed big on the box.
- Adding every appliance’s starting surge together.
- Buying far more than you need. Bigger means more fuel, noise and weight.
- Planning on extension cords for a furnace or well pump. Those need a transfer switch.
If you’ll connect the generator to your house, an electrician can tell you which circuits matter, install an inlet and interlock or transfer switch, and confirm the generator’s outlet matches.
Is 3,500 watts enough, and other sizing checks
Is 3,500 watts enough for a house?
For a fridge, lights, internet and a few small loads, often yes. Not for a well pump plus other loads.
What size for a whole house?
Usually beyond portables. See running a whole house on a portable.
Do I need a 30 amp outlet?
For a home transfer switch, an L14-30 is the usual minimum. For an RV, a TT-30 is convenient.
Is a dual-fuel model worth it?
Often yes for home backup. Propane stores indefinitely, so your generator is ready even if gasoline is scarce after a storm.
Specific cases: refrigerator, RV fridge and AC, and the sizing hub.
