Running watts vs. starting watts
Running watts keep an appliance going. Starting watts (surge) are the short spike, 2–3× higher, that motors need to start: fridges, pumps, AC units, furnace blowers. A generator must cover all running watts plus the biggest single start-up spike.
Typical generator sizes for home backup
| Scenario | Running load | Recommended size |
|---|---|---|
| Essentials: fridge, lights, Wi-Fi, phones | 210 W | 300 W running / 1,300 W starting |
| Essentials + sump pump | 1,235 W | 1,500 W running / 2,400 W starting |
| Essentials + furnace fan (winter) | 1,085 W | 1,400 W running / 2,700 W starting |
| Essentials + well pump + window AC | 3,375 W | 4,100 W running / 4,500 W starting |
Appliance wattage chart
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator (full size) | 150 W | 1,200 W |
| Chest freezer | 100 W | 800 W |
| Sump pump (1/2 HP) | 1,050 W | 2,150 W |
| Well pump (1/2 HP) | 1,000 W | 2,100 W |
| Furnace blower fan (1/2 HP) | 800 W | 2,350 W |
| Window AC (8,000 BTU) | 700 W | 1,800 W |
| Microwave (1000 W) | 1,500 W | 1,500 W |
| Coffee maker | 900 W | 900 W |
| Space heater (high) | 1,500 W | 1,500 W |
| Washing machine | 500 W | 1,200 W |
| Garage door opener | 550 W | 1,100 W |
| TV (55" LED) | 100 W | 100 W |
| Wi-Fi router + modem | 15 W | 15 W |
| LED light bulb | 10 W | 10 W |
| Circular saw | 1,400 W | 2,300 W |
| Air compressor (small) | 1,000 W | 2,000 W |
Central AC (3-ton) typically needs 3,500–5,000 W running and 10,000+ W to start without a soft-start kit. An electric water heater or dryer adds 4,000–5,500 W each.
Inverter, portable or standby?
| Type | Typical size | Best for |
|---|---|---|
| Inverter generator | 2,000–4,500 W | Quiet, clean power for electronics, camping, RV |
| Portable (open frame) | 5,000–13,000 W | Whole-house essentials through a transfer switch |
| Standby (installed) | 10,000–26,000 W | Automatic whole-home backup, runs on natural gas/propane |
| Battery power station | 1,800–6,000 W | Silent, indoor-safe, no fuel; best with solar |
Safety first
- Never run a fuel generator indoors, in a garage or near windows. Carbon monoxide kills.
- Connect to house wiring only with a transfer switch or interlock installed by a licensed electrician. Back-feeding endangers utility workers.
- Store fuel safely and run the generator monthly to keep it ready.
Frequently asked questions
What size generator do I need to run a house?
Most homes can run essentials (fridge, freezer, lights, sump pump, furnace fan, Wi-Fi) on 5,000–7,500 running watts. Running central AC, an electric water heater or range usually requires 10,000–15,000 W or a standby generator.
What size generator do I need for a refrigerator?
A fridge alone needs about 150–200 W running and up to 1,200 W to start, so even a 2,000 W inverter generator works. Add other appliances to the calculator to size for the total.
Will a 3500 watt generator run a house?
It runs a fridge, lights, Wi-Fi, a TV and a sump pump, but not at the same time as a microwave or window AC. Use the calculator to check your exact mix.
Is a power station better than a generator?
For loads under ~1,800 W and indoor use, yes: silent, no fumes, no fuel. For multi-day outages with big loads like well pumps or AC, a fuel generator is cheaper per watt.