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What size generator do I need to run a CPAP overnight?

Q: What size generator do I need to run a CPAP overnight?

Plan on at least 250 running watts and 250 watts of surge capacity. That covers 200W of running load plus the largest start-up surge, with 25% headroom.

Overnight medical and comfort loads are tiny — the real requirements are run-time, fuel efficiency, and quiet, not watts.

The load

CPAP machine — 60W running
Box fan — 100W running, 150W starting
Phone charger — 10W running
LED lights (per room) — 30W running

SIZING PLATE4 LOADS · +25% HEADROOM

Total running watts

200 W

Peak (largest start)

250 W

Buy at least

250 W rated

Look for ~250W running / 250W surge or better.

Field note: Turn off the CPAP's heated humidifier to cut its draw by two-thirds. For medical equipment, pair any generator with a battery backup so a stall or refuel gap never interrupts therapy, and verify draw against your unit's label.

Right size: Small inverter (1,800W / 2,200W surge)

Typical price $500-1,100 · e.g. Honda EU2200i, Champion 2500 dual-fuel, Predator 2000

Camping, tailgates, home office, CPAP and overnight essentials, one small appliance at a time. Quiet and light, but one large compressor surge can max it out.

See current prices on Amazon

One size up: Mid-size inverter (3,500W / 4,000W surge)

Typical price $600-1,400 · e.g. Champion 4250 open-frame inverter, Westinghouse iGen4500, Generac GP3500iO

RV 13,500 BTU AC (especially with soft-start), fridge + window AC, storm essentials for smaller homes. The sweet spot of quiet, portability, and real capacity for most first-time buyers.

See current prices on Amazon

Adjust for your setup

Different fridge? Bigger AC? Uncheck and re-check below — the plate recomputes live.

SIZING PLATE4 LOADS · +25% HEADROOM

Total running watts

200 W

Peak (largest start)

250 W

Buy at least

250 W rated

Look for ~250W running / 250W surge or better.

Peak assumes your largest motor starts while everything else runs — the honest worst case. Start big motors one at a time and a smaller unit may cope, but this number won't let you down.

Kitchen Refrigerator (full-size) 300W run / 1500W start Mini fridge 90W run / 700W start Chest freezer 250W run / 1200W start Microwave (1000W) 1400W run Electric range (one burner) 1500W run Coffee maker (drip) 900W run Toaster 1100W run Electric kettle 1400W run Dishwasher 1300W run / 1500W start Instant Pot / multicooker 1000W run

Heating & cooling Window AC (5,000 BTU) 500W run / 1500W start Window AC (8,000 BTU) 800W run / 2200W start Window AC (12,000 BTU) 1100W run / 3000W start Central AC (3-ton) 3500W run / 8500W start Space heater (1500W) 1500W run Furnace blower fan (gas furnace) 600W run / 1600W start Heat pump (2-ton) 2500W run / 6000W start Box fan 100W run / 150W start Ceiling fan 75W run / 100W start

Pumps & well Sump pump (1/3 HP) 800W run / 1500W start Sump pump (1/2 HP) 1050W run / 2200W start Well pump (1/2 HP) 1000W run / 2100W start Well pump (1 HP) 2000W run / 4000W start Sewage ejector pump (1/2 HP) 1000W run / 2200W start

Electronics TV (55" LED) 80W run Wi-Fi router + modem 15W run Laptop 65W run Desktop PC + monitor 350W run / 400W start Phone charger 10W run Starlink dish + router 75W run / 100W start

Medical & safety CPAP machine 60W run Oxygen concentrator 350W run / 600W start

Lighting LED lights (per room) 30W run

Laundry Washing machine 700W run / 1600W start Clothes dryer (electric) 5000W run / 6000W start Clothes dryer (gas) 700W run / 1800W start

Household Garage door opener (1/2 HP) 550W run / 1200W start Water heater (electric tank) 4500W run EV charging (Level 1, 120V) 1400W run

Tools & outdoor Circular saw 1400W run / 2300W start Air compressor (1 HP) 1500W run / 3000W start Welder (140A MIG) 3500W run / 4000W start

RV & camping RV air conditioner (13,500 BTU) 1300W run / 2900W start RV converter/charger 500W run Electric griddle 1200W run Slow cooker 250W run

Generators that fit

Right size: Small inverter (1,800W / 2,200W surge)

Typical price $500-1,100 · e.g. Honda EU2200i, Champion 2500 dual-fuel, Predator 2000

Camping, tailgates, home office, CPAP and overnight essentials, one small appliance at a time. Quiet and light, but one large compressor surge can max it out.

See current prices on Amazon

One size up: Mid-size inverter (3,500W / 4,000W surge)

Typical price $600-1,400 · e.g. Champion 4250 open-frame inverter, Westinghouse iGen4500, Generac GP3500iO

RV 13,500 BTU AC (especially with soft-start), fridge + window AC, storm essentials for smaller homes. The sweet spot of quiet, portability, and real capacity for most first-time buyers.

See current prices on Amazon

This site earns commissions from qualifying purchases made through links to Amazon and other retailers, at no extra cost to you. Wattage figures are typical estimates — actual draw varies by model. Always verify against your appliance's nameplate, and consult a licensed electrician for any panel or hardwired connections.