Generator size by appliance
Each page gives one appliance's running watts, the extra watts it draws while starting, and which generators can carry it alone or with a refrigerator, lights and phone chargers. Add several at once in the calculator.
| Appliance | Running W | Extra to start | Needed alone |
|---|---|---|---|
| Refrigerator/freezer | 700 | 2,200 | 2,900 |
| Sump pump, 1/2 hp | 1,050 | 2,150 | 3,200 |
| Well pump, 1/2 hp | 1,000 | 2,100 | 3,100 |
| Furnace fan blower, 1/3 hp | 700 | 1,400 | 2,100 |
| Window air conditioner, 12,000 BTU | 3,250 | 3,950 | 7,200 |
| Central air conditioner, 24,000 BTU (2 ton) | 3,800 | 4,950 | 8,750 |
| Heat pump | 4,700 | 4,500 | 9,200 |
| Space heater | 1,500 | — | 1,500 |
| Electric water heater | 4,500 | — | 4,500 |
| Washing machine | 1,150 | 2,300 | 3,450 |
| Garage door opener, 1/2 hp | 875 | 2,350 | 3,225 |
| CPAP machine (ResMed AirSense 11) | 73.2 | — | 73.2 |
| Oxygen concentrator (Philips EverFlo) | 350 | — | 350 |
Figures from the Generac GP brochure, EWEB, Champion's flyer, ResMed and Philips; each page names its row. "Needed alone" is running plus additional starting watts.
Why starting watts matter more than running watts
Motors — compressors, pumps, fans — draw a surge for a few seconds as they start. A generator has to supply that surge on top of everything already running, so the device with the biggest surge often sets the size of the generator, not the total running load. Resistive loads such as space heaters and toasters have no surge in these tables but draw a lot of power the whole time. The running vs starting watts guide explains the method and why the tables disagree.
Kitchen and comfort loads
Heating and cooling loads are the big ones. A central air conditioner or heat pump, an electric water heater or an electric range element each needs several thousand watts — usually more than a portable can spare once the essentials are running, which is where standby generators come in.