A CPAP commonly needs roughly 20–40 watts when the blower is running without heating, while a humidifier and heated tube can push a planning estimate into roughly the 40–100 watt range. Those are broad planning values—not specifications for every machine. Your model, pressure, mask leak, climate, humidity setting and tube temperature can all change the actual draw.
A 30 W setup uses about 240 Wh at the CPAP. A 60 W setup uses about 480 Wh. The battery must be larger than those numbers because reserve capacity, aging and AC/DC conversion losses reduce usable energy.
For a personalized result, use the free CPAP battery backup runtime calculator. It includes battery health, starting charge, reserve, AC or DC efficiency, accessory loads and treatment hours.
How many watts does a CPAP machine use?
There is no single wattage that fits every CPAP. The blower adjusts to the treatment pressure and airflow needed at that moment. Heating accessories can add a separate and sometimes much larger load.
| CPAP setup | Broad planning draw | Eight-hour energy |
|---|---|---|
| Travel CPAP without heating | About 15–25 W | 120–200 Wh |
| Full-size CPAP without heating | About 20–40 W | 160–320 Wh |
| CPAP with humidifier | About 40–70 W | 320–560 Wh |
| Humidifier and heated tube | About 60–100 W | 480–800 Wh |
Use this table only for early planning. Check the power label and user manual for your exact CPAP, then measure a normal night if possible. A plug-in energy meter provides far better evidence than choosing a number from a generic list.
Watts and watt-hours are not the same
Watts (W) measure power at a moment in time. Watt-hours (Wh) measure energy used over time. A machine drawing 30 W for eight hours consumes:
People sometimes say “watts per hour,” but that is not the quantity needed for battery sizing. For an overnight backup, multiply average watts by treatment hours to get watt-hours.
How much electricity does a CPAP use per night?
The basic device-energy calculation is straightforward:
- 20 W for eight hours: 160 Wh
- 30 W for eight hours: 240 Wh
- 60 W for eight hours: 480 Wh
- 80 W for eight hours: 640 Wh
This is energy at the device. It does not yet include inverter loss, battery aging or the reserve you keep to prevent an unexpectedly empty pack.
Why the power adapter rating is not average consumption
A CPAP power brick may show a much higher wattage than the machine normally draws. That label describes the supply’s supported output or maximum design condition; it does not prove the CPAP continuously consumes that amount.
Sizing a battery only from the adapter’s maximum can overestimate routine energy use. Sizing from an optimistic blower-only number can underestimate a cold night with active heating. Measure the real setup with the humidifier, tubing and settings you actually use.
What changes CPAP wattage?
Humidifier heating
Heating water requires energy. The humidifier may cycle rather than remain at maximum power, so room temperature, humidity and the selected setting affect its average draw.
Heated tubing
A heated tube adds another electrical load. Its demand depends on the target temperature and surrounding conditions.
Pressure and airflow
Higher airflow generally requires more blower work. Mask leak can also make the machine move more air than a well-sealed setup.
AC versus DC power
A power station’s AC outlet uses an inverter, which consumes some stored energy. A manufacturer-approved DC connection can be more efficient, but voltage, polarity, connector and device compatibility must all be correct.
Battery temperature and age
Cold conditions and an aging battery can reduce usable capacity. That is why the calculator includes battery health and a reserve instead of assuming every advertised watt-hour reaches the CPAP.
What size battery backup do you need for a CPAP?
Use this more realistic sizing formula:
Suppose the battery is at 95% health and you keep a 15% reserve:
| Setup | Connection | Approximate minimum for 8 hours |
|---|---|---|
| 30 W, no heating | 95% efficient DC | About 313 Wh |
| 60 W, humidifier | 85% efficient AC | About 699 Wh |
| 80 W, heating accessories | 85% efficient AC | About 932 Wh |
These examples are calculated planning minimums, not guarantees. A battery-management system may shut down before the displayed charge reaches zero, and real CPAP demand can vary through the night.
AC outlet or DC cable: which lasts longer?
DC can often provide longer runtime because the battery does not need to create household AC and then have the CPAP power brick convert it back to DC. However, efficiency is secondary to safety and compatibility.
Never assume a connector that physically fits is electrically correct. Use the CPAP manufacturer’s approved power option and follow the battery manufacturer’s output limits. If you are comparing a portable power station, the power station runtime calculator can model its efficiency and usable capacity.
How to measure your CPAP’s real overnight energy use
- Connect the CPAP through a reliable plug-in energy meter.
- Use the same humidifier, heated tube and comfort settings you normally use.
- Run the machine for a complete typical night.
- Record total watt-hours rather than only the highest watt reading.
- Repeat on another night if conditions vary significantly.
- Add a conservative reserve when choosing backup capacity.
If you only know battery capacity and average load, the general battery backup time calculator provides a second way to check the result.
Can you turn off the humidifier to save power?
Disabling optional heating may reduce electrical demand, but comfort and treatment use matter. Do not change prescribed pressure or clinical settings based on a battery calculation. Follow the device instructions and discuss treatment questions with your clinician.
Frequently asked questions
How many watts does a CPAP use in eight hours?
Watts describe power, not an eight-hour total. A CPAP averaging 30 W uses 240 Wh in eight hours, while a 60 W setup uses 480 Wh before battery losses.
How long will a 500 Wh battery run a CPAP?
It depends on load and losses. At 60 W, 95% battery health, a 15% reserve and 85% AC efficiency, the estimate is about 5.7 hours. The CPAP calculator lets you change every assumption.
Does a CPAP use more power with a humidifier?
Usually yes, because the machine must heat water. Heated tubing can add further demand. The increase varies with the device, setting and room conditions.
Will a 300 W power station run a CPAP?
The 300 W rating usually describes maximum output, not stored energy. You also need the battery capacity in Wh. A power station can support the watts but still have too few watt-hours to last overnight.
Should I size from the CPAP adapter label?
Use the label to confirm electrical requirements and maximum supply capability, but measure typical energy use for runtime planning. The adapter rating is not necessarily the machine’s continuous draw.