For a CPAP, a battery power station charged by solar or the car may be quieter than a generator. Check the CPAP's power use with and without the heated humidifier.
How the generator calculator works
GeneratorSize multiplies each appliance's running watts by its quantity and adds them up. For every appliance it works out the extra starting surge (starting watts − running watts) and adds only the largest one, assuming one motor starts at a time. The recommended running rating is the running total plus your headroom, rounded up to 10 W. Current is watts ÷ 120 V, or ÷ 240 V for a 120/240 V generator with the load split evenly between its two legs.
Biggest starting surges in the list
| Appliance | Running W | Starting W | Extra surge |
|---|---|---|---|
| Central AC 3 ton (240 V) | 3,500 | 10,500 | 7,000 |
| Air compressor 1 HP | 1,600 | 4,500 | 2,900 |
| Window AC 10,000 BTU | 1,200 | 3,600 | 2,400 |
| RV air conditioner 15,000 BTU | 1,800 | 3,500 | 1,700 |
| Furnace fan ½ HP (gas or oil furnace) | 800 | 2,350 | 1,550 |
| Refrigerator / upright freezer | 700 | 2,200 | 1,500 |
| RV air conditioner 13,500 BTU | 1,500 | 3,000 | 1,500 |
| Garage door opener ½ HP | 875 | 2,350 | 1,475 |
Generator types by size
| Running watts | Typical type |
|---|---|
| Up to 2,500 | small inverter generator (about 2,000–2,500 W) |
| 2,500 – 4,500 | mid-size inverter or portable generator |
| 4,500 – 12,000 | large portable generator |
| Over 12,000 | home standby generator |
Wattages are typical figures of the kind published in generator makers' wattage charts; real appliances vary with age, size and efficiency, so use the data plate where you can. Have an electrician install any transfer switch or interlock, run generators outdoors away from windows and doors (carbon monoxide), and use a CO alarm indoors.
Frequently asked questions
What size generator do I need for camping?
For lights, a fan, chargers, a CPAP and a mini fridge, 1,000 to 2,000 watts is plenty. Add a coffee maker or kettle and you need around 2,000 W.
Can a 2,000 watt generator run a coffee maker?
Yes, a typical 1,000 W coffee maker, but not at the same time as a 1,500 W kettle.
How much power does a CPAP use?
Often 30 to 60 watts without the humidifier and noticeably more with heated humidification.
Is GeneratorSize free?
Yes, with no sign-up or ads.
Is my list saved?
Yes, in this browser only.