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
Why the inverter type matters as much as the wattage
A worked example

How this guide breaks the problem down. Jump to any part.

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.