guide · energy
How Many Watts Does a CPAP Use?
Updated November 5, 2026 · 6 min read
direct answer
Between 5 W and 60 W, and the heaters decide where you sit. ResMed measures the AirSense 10 AutoSet at 7 W with nothing heated, 22 W with the humidifier on and 34 W with a ClimateLineAir heated tube added. Bi-level machines measured 41 to 44 W by the same test-lung method. The 90 W on the power brick and the 104 W peak on the label are ceilings, not consumption.
The single number that most CPAP battery advice gets wrong is the watt figure. Quote the label and you buy a battery two or three times the size you need; quote a forum and you may be 20 W out on a heated tube. Here is where the real figures come from and how to turn them into runtime.
The measured figures
A CPAP is a small blower with up to two resistive heaters, and the heaters do almost all of the work. ResMed publishes bench measurements taken on a test lung at a typical therapeutic pressure, which is the closest thing to a fair "how much does it pull" number available:
| Machine and setting | Metered watts | Watt-hours per 8 h night | Amp-hours drawn at 12 V |
|---|---|---|---|
| Travel unit, no humidifier, no tube heat | 5–10 W | 40–80 Wh | 3.3–6.7 Ah |
| AirSense 10 AutoSet, pressure only | 7 W | 56 Wh | 4.7 Ah |
| AirSense 10 AutoSet + humidifier | 22 W | 176 Wh | 14.7 Ah |
| AirSense 10 AutoSet + humidifier + ClimateLineAir | 34 W | 272 Wh | 22.7 Ah |
| AirCurve 10 VAuto (bi-level), heated | 41 W | 328 Wh | 27.3 Ah |
| CS PaceWave (bi-level, VPAP), heated | 44 W | 352 Wh | 29.3 Ah |
The pattern is worth memorising before you shop for anything: the blower is nearly free and the heat is the bill. Turning the humidifier from its maximum to a low setting, or giving up the heated tube and using a cotton tube sleeve, routinely halves the draw.
Why the label says 53 W and the brick says 90 W
Two different documents describe the same machine, and neither is lying:
- The rating label states the electrical envelope the device may be operated within — the AirSense 10 reads 53 W typical and 104 W maximum. "Typical" there assumes the humidifier and tube heater are switched to their highest settings, which is not how most people sleep.
- The power adapter is rated for its output capacity, commonly 90 W on a modern ResMed brick. A 90 W supply running a 7 W machine is not consuming 90 W; it is a supply that could deliver 90 W. Sizing a battery from the adapter's nameplate is the most common way people end up buying three times the capacity they need.
- Peak figures exist because the load is not smooth. The blower's demand rises with pressure and with leak compensation, and the heaters draw in bursts as they chase the set humidity and tube temperature.
Use the metered figure for runtime, and keep the label figure in mind only as the headroom a converter or inverter must tolerate without tripping.
Watts, watt-hours and amp-hours are three different questions
Most CPAP battery arguments are unit confusion. Watts are a rate. Watt-hours are an amount. Amp-hours are the same amount seen from the battery's voltage:
Watt-hours = amp-hours × volts, so amp-hours = watt-hours ÷ volts
→ a 34 W machine for 8 h = 272 Wh = 22.7 Ah out of a 12 V battery
That division is why "100 Ah" tells you nothing on its own. At 12 V a 100 Ah battery is 1,200 Wh, so a 272 Wh night is a bit over four of them — but only 3.7 nights once a lithium pack's 85% usable limit is applied, and 2.2 if it is the AGM deep-cycle the camper already owns. The amps-to-watts calculator does the same conversion at any voltage, and watt hours explained covers why the number on a battery box is never the number you get.
What moves the number during the night
| Factor | Direction | Typical size of the effect |
|---|---|---|
| Humidifier setting | Up | +15 W from off to a mid setting — the largest single lever |
| Heated tube | Up | +12 W at 30 C on a ClimateLineAir |
| Therapeutic pressure | Up | The blower works harder; the metered figures are taken at a typical treatment pressure |
| Mask leak | Up | The blower works to replace leaked air; a bad seal can add several watts |
| Altitude | Up | Thinner air changes blower load; machines compensate automatically |
| Colder room | Up | The tube heater and humidifier run longer to hit their setpoints |
| Ramp / pressure relief | Down | Lower average pressure early in the night |
The direction of the "colder room" row is the reason winter camping battery plans fail: the same machine pulls more power in a cold tent, and the same battery delivers less of it. Both effects push the same way, and the CPAP battery calculator applies both.
The 70 to 100 W myth that oversizes every battery
Search for a CPAP's power draw and a lot of results say 70 W, 90 W or "plan for 100 W". Those figures come from reading the adapter's rating or the maximum on the label, and they propagate into sizing advice that tells someone with a 7 W travel machine to buy a 1,000 Wh station. The arithmetic is easy to check: if a CPAP really drew 100 W, an eight-hour night would be 800 Wh, and a 96 Wh airline battery would last under one hour. It does not: a 10 W travel unit on the same 96 Wh pack runs about eight hours.
Where a high figure is genuinely right is a large bi-level machine with a heated humidifier, a heated tube and a high pressure, running in a cold room — which is exactly the case the label has to cover. If your setup is that, put 45 to 55 W into the calculator rather than 100 W, and keep a night of margin.
What a night of therapy costs on the grid
For scale, at the US average residential rate of 18.16 cents per kWh (EIA Electric Power Monthly, Table 5.6.A, August 2026):
| Configuration | Average watts | kWh per night | Cost per night | Cost per year |
|---|---|---|---|---|
| Travel unit, no heat | 10 W | 0.080 | 1.5¢ | $5.30 |
| Pressure only | 7 W | 0.056 | 1.0¢ | $3.71 |
| Humidifier on | 22 W | 0.176 | 3.2¢ | $11.67 |
| Humidifier + heated tube | 34 W | 0.272 | 4.9¢ | $18.03 |
| Bi-level, maximum heat | 55 W | 0.440 | 8.0¢ | $29.17 |
A nightly CPAP is a few cents of electricity. That is the honest frame for the purchase in front of you: a battery is not buying you cheaper therapy, it is buying you therapy where there is no outlet — and the whole cost of that battery is worth it exactly once, when the power goes out on a night you would otherwise not sleep.
Two more pages finish the job: the CPAP battery size chart turns these watt figures into nights for every common pack size, and how to run a CPAP on battery covers the wiring, the recharge plan and the airport. The energy tools hub has the rest of the set.
try it with your numbers
CPAP Battery Runtime Calculator
Put your metered watts, your battery's watt-hours and the path between them into the calculator and get nights of sleep — with depth of discharge, converter losses, cold and the FAA carry-on check counted.
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Frequently Asked Questions
The watt questions people ask before they buy a battery.
How many watts does a CPAP use?
Between 5 W and 60 W, and the heaters decide where you sit. ResMed measures the AirSense 10 AutoSet at 7 W with nothing heated, 22 W with the humidifier on and 34 W with a ClimateLineAir heated tube added; bi-level machines measured 41 to 44 W by the same test-lung method.
Why does my CPAP's label say 100 W?
A nameplate rating has to cover the worst case the manufacturer will not prevent: maximum humidifier and tube heat, the highest rated altitude, and the capacity of the wall adapter. The AirSense 10's power brick is rated 90 W and the label reads 53 W typical with a 104 W maximum, while the same machine on a test lung measured 34 W fully heated. For runtime and cost, use the metered figure.
How many watt-hours does a CPAP use per night?
Multiply the average draw by the hours worn. Eight hours at 7 W is 56 Wh, at 22 W it is 176 Wh, and at 34 W it is 272 Wh. In amp-hours at 12 V those are 4.7 Ah, 14.7 Ah and 22.7 Ah, which is why a 100 Ah battery is not the week of runtime the amp-hour figure suggests at 34 W.
Does a CPAP use a lot of electricity?
No. A 34 W machine running eight hours a night uses 0.272 kWh per night and about 99 kWh a year, which at the US average residential rate of 18.16 cents per kWh is under 5 cents a night and roughly $18 a year. The battery that replaces that grid supply costs far more than the electricity it saves.
Do travel CPAPs use less power?
Usually less than a third. A travel unit on a test lung draws about 5 to 10 W with no humidifier and no tube heater, which is why a 96 Wh airline power bank covers a full night of a 10 W machine and only about a third of a night at 34 W.