How Many Watts Does a CPAP Use?

If you're planning backup power for a CPAP machine, the single biggest factor isn't the brand of power station you buy — it's whether you run a heated humidifier. That one setting can nearly triple your CPAP's power draw, and it's the difference between a power station lasting all night or running out around 3am.

General power-math guide, not medical advice. Confirm exact power requirements with your CPAP manufacturer or DME provider.

Why the humidifier changes everything

A CPAP machine without heated humidification typically draws 20-40W continuously — mostly the motor pressurizing air through the mask. That's a light, steady load, comparable to a laptop charger.

Turn on a heated humidifier and the draw jumps to 60-90W, and up to 100-120W on high-heat settings, because the machine is now also running a heating element to warm and humidify the air. This isn't a minor bump — it's roughly 2-3x the baseline draw.

In this project's own worked example, that difference was enough to flip which power station was the better buy: a smaller, cheaper unit was fine without a humidifier but fell well short of an 8-hour night with one running.

Why the inverter type matters as much as the wattage

CPAP machines convert the AC power from a wall outlet or power station back into DC internally. That conversion relies on a clean, consistent AC waveform — which is exactly what 'pure sine wave' means.

A modified sine wave inverter approximates a sine wave with a rougher, stepped signal. Most electronics tolerate this fine, but a CPAP's power supply is sensitive enough that it can respond with buzzing, overheating, or erratic behavior. This is a real equipment-safety issue, not a nitpick — see the dedicated pure sine wave guide for more.

A worked example

Take a 500Wh power station running a CPAP at 75W (a moderate humidifier setting) through a typical AC inverter, which loses roughly 25% of capacity to conversion inefficiency: usable runtime is roughly 500 × 0.75 ÷ 75 ≈ 5 hours — short of a full night. The same unit at 30W (no humidifier) would run roughly 12.5 hours — comfortably past 8 hours.

Key Facts At a Glance

Without heated humidification: ~20-40W continuous
With heated humidifier: ~60-90W, up to 100-120W on high-heat setups
A 400W inverter covers most CPAPs comfortably, even with humidification
Requires a pure sine wave inverter — modified sine wave can cause buzzing, power-supply overheating, or erratic behavior
Rule of thumb: without humidifier, 120-240Wh covers an 8-hour night; with humidifier, plan for 270-500Wh

FAQ

Will a 400W inverter be enough for my CPAP?

Almost always yes on the output side — even with heated humidification, most CPAPs draw well under 120W, so a 400W-rated inverter has comfortable headroom. The real constraint is battery capacity (Wh) for the runtime you need, not the inverter's wattage rating.

Do I need to know my CPAP's exact wattage, or is a general estimate enough?

A general estimate is a reasonable starting point for comparing power stations, but for your actual purchase decision, check your CPAP's power supply label or manual for its exact rated wattage — models vary, and this guide's ranges are typical, not universal.

Sources

/best/power-stations/cpap/ · /tools/power-station-runtime-calculator/ · /learn/pure-sine-wave-vs-modified-sine-wave/