How many watts does a CPAP machine use? About 25–40 watts with the humidifier switched off, and 50–95 watts with it on, which works out to roughly 200–650 watt-hours across an eight-hour night and 70–320 kilowatt-hours a year. The blower is not what drains a battery. The heater is, and it is optional.
The three numbers, and which one matters
A CPAP has three separate wattage figures, and the sizing mistakes come from quoting one when you needed another.
| Number | Typical value | What it is for |
|---|---|---|
| Running watts, humidifier off | 25–40W | The blower on its own |
| Running watts, humidifier and heated hose on | 50–95W | What most people actually draw |
| Peak draw, heater at full power | 80–110W | Sizing the inverter output |
| Energy per night | 200–650Wh | Sizing the battery |
The narrow peak column is the useful part. A CPAP cannot draw much more than its external power supply is rated for, and those bricks are commonly rated in the 65–90W region, with larger bilevel machines a little above that. The ceiling is built into the hardware.
So a CPAP is the opposite of a refrigerator. With a fridge the inverter output rating is the hard constraint. With a CPAP, output is a non-issue, because almost any power station on sale clears 110W several times over. The only question is how many watt-hours you have stored.
Why the humidifier decides everything
The blower is a small brushless DC motor moving air at low pressure, and it is genuinely efficient. Its draw tracks your prescribed pressure and how well the mask seals: around 6–8 cmH2O on a well-fitted mask sits near the bottom of the 25–40W band, while a prescription in the mid-teens, or a leak the machine spends all night compensating for, sits near the top.
The heated humidifier is a different kind of load. It is a resistive plate pulling 50–85W while it heats, and it cycles to hold temperature the way an oven element does, so what matters is the share of the night it spends switched on. In a warm bedroom on a low setting that might be 30% of the night. In a cold room on a high setting it can be most of it.
Things that push the night’s total up:
- Humidity setting. The biggest lever by a wide margin. High to off typically cuts the night’s energy by half to two thirds.
- A cold bedroom. The heater is fighting the room, so the same machine on the same settings uses noticeably more in January than in July.
- A heated hose. Adds roughly 10–20W, and it is warming whenever the humidifier is.
- Mask leak. The blower works harder to hold pressure, and on an auto-adjusting machine a leak can drive the pressure up as well.
- Machine age. Older units tend to sit 10–20W above a current equivalent for the same job, mostly in the power supply.
The humidifier is a battery decision, not a nightly one. Switching it off is the correct move when you are running from a power station in an outage, because it roughly doubles or triples your runtime. It is not a sensible way to save money on the electricity bill — the whole humidifier costs about twenty dollars a year to run.
How many watts does a CPAP machine use, by setup
The table below assumes an eight-hour night, which is the honest basis for anything battery-related. Multiply the per-night figure by your own average sleep hours if you use it less.
| Setup | Average watts | Per night (8 hrs) | Per year |
|---|---|---|---|
| Travel or mini CPAP, no humidifier | 15–30W | 120–240Wh | 45–90 kWh |
| Standard CPAP, humidifier off | 25–40W | 200–320Wh | 70–115 kWh |
| Standard CPAP, humidifier on, moderate setting | 50–80W | 400–640Wh | 145–235 kWh |
| CPAP, humidifier and heated hose, high setting | 70–110W | 560–880Wh | 205–320 kWh |
| Bilevel or BiPAP, humidifier off | 30–55W | 240–440Wh | 90–160 kWh |
| Bilevel or BiPAP with humidifier | 60–95W | 480–760Wh | 175–280 kWh |
| Machine left plugged in but idle, per 16-hour day | 1–3W | 15–50Wh | 6–18 kWh |
The highlighted row is the one to plan a battery around, because it is the configuration you should be in when the power is out. The rest of the table is what you use on a normal night at the wall, where none of it costs enough to think about. To turn any row into a bill figure with your own hours and rate, use the watts to kWh calculator.
Startup surge: there isn’t one
Refrigerators, pumps and air conditioners spike to several times their running wattage the moment the motor starts, which is why they need inverter headroom. A CPAP does not, and that is worth saying plainly rather than inventing a number for it.
The blower is a small DC motor spun up gently under electronic control, fed from a switch-mode power supply, so there is no locked-rotor inrush. The only transient is the brick charging its own capacitors at plug-in, lasting milliseconds and well inside what any inverter tolerates. The largest step the machine ever asks for is the humidifier plate switching on: a step to about 100W, not a spike to 500W.
Do not buy output capacity for a surge that does not exist. A 150W continuous pure sine inverter is technically sufficient, and in practice you will end up with something far larger anyway, because the capacity you need for a full night comes attached to a bigger inverter.
Pure sine wave matters more than watts here. Modified sine wave inverters — the cheap ones sold for cars — can make some medical power supplies buzz, run hot or refuse to start. Essentially every lithium power station on sale outputs pure sine, but confirm it on the spec sheet before you rely on the unit overnight.
How long each power station really runs a CPAP
The assumptions, up front, because runtime tables without them are worthless. Usable capacity is 85% of the rated figure, covering inverter conversion loss and the fact that a pack never delivers its full label. The load is 30W humidifier-off and 70W with humidifier and heated hose at a moderate setting, plus 8W for the inverter simply being switched on — a real cost most tables ignore, and one that matters enormously when the load itself is only 30W.
| Capacity | Usable | Humidifier off (38W) | Humidifier on (78W) |
|---|---|---|---|
| 300Wh | ~255Wh | ~6.5 hrs, short of a night | ~3 hrs |
| 500Wh | ~425Wh | ~11 hrs, one night | ~5 hrs |
| 1,000Wh | ~850Wh | ~22 hrs, two nights | ~11 hrs, one night |
| 2,000Wh | ~1,700Wh | ~44 hrs, five nights | ~21 hrs, two nights |
| 3,600Wh | ~3,060Wh | ~80 hrs, ten nights | ~39 hrs, four nights |
On the numbers. Capacity and output are manufacturer specifications. Expect 80–90% of rated capacity in real use after inverter losses, and less in cold weather.
Two rows deserve comment. The 300Wh bracket is the wrong tool. It is the size most often recommended for CPAP backup, and once the inverter’s own consumption is counted it does not reliably survive one eight-hour night. It gets you five or six hours and then stops, which is worse than useless if the point was not waking up without therapy. Treat 500Wh as the floor for one night, and 1,000Wh as the floor for a second night or for keeping the humidifier on.
At the other end, 3,600Wh bought purely for a CPAP is a lot of money sitting idle. That size earns its place when the CPAP is one item on a list that also includes a refrigerator and some lighting, at which point you are sizing an outage kit rather than a CPAP battery. The power station finder filters by capacity once you know your number.
Skip the inverter and the numbers improve
Most CPAP manufacturers sell a regulated DC cable that runs the machine from a 12V socket with no inverter in the path. That removes the conversion loss and the 8W idle penalty together, and typically buys 25–30% more runtime from the same battery. Driven this way, a 500Wh unit covers a humidifier-off night with margin rather than scraping it.
The catch is that humidification usually will not run from DC, which in an outage is the setting you were turning off anyway. If you are sizing a deep-cycle battery instead of a power station, 30W at 12V is about 2.5 amps; the watts to amps calculator handles other voltages, and amp hours to watt hours converts an Ah rating into the watt-hour figure the table uses.
Use the manufacturer’s DC cable, not a generic one. These machines want a regulated supply at a specific voltage. A generic car adapter that looks like it fits can deliver the wrong voltage under load. This is the one place in the whole setup where improvising is a bad idea.
How to measure your own machine in one night
Every figure on this page is a range. Your machine, at your pressure and your humidity setting, is a single number you can have for about twenty-five dollars.
- Buy a plug-in energy monitor — the type that sits between the plug and the socket and totals kilowatt-hours.
- Plug the CPAP in through it and zero the counter before bed.
- Sleep a normal night on your normal settings. Do not tidy up the humidity setting for the test.
- Read the kWh total in the morning and multiply by 1,000 for watt-hours per night.
- Repeat with the humidifier off. The gap between the two numbers is your outage budget.
Two nights of measurement replaces this entire article for your specific machine. Take the humidifier-off figure, divide by 0.85 for inverter losses, and that is the minimum usable capacity you need. Cheap monitors are imprecise below about 5W, but at 30–80W any of them is accurate enough for sizing. While the monitor is out, measure the router and the fridge as well and most of your outage load list is measured rather than guessed — the same approach scales to a whole house.
Whether a CPAP belongs on battery backup
This site says no to most battery purchases. This is one of the clear yeses.
The case is unusually good: the load is tiny, the duration is predictable, and the alternative is unattractive. A CPAP asks for 200–320Wh a night with the humidifier off, which a mid-size power station supplies several times over. Outages do not arrive at convenient hours, and a battery is silent, indoors, and needs nobody to walk outside and start it at three in the morning.
What to buy, in short:
- One night of cover: 500Wh, humidifier off. Confirm the unit is pure sine.
- Two or three nights, or humidifier on: 1,000Wh. The sensible default for most people.
- Multi-day outages with other loads: 2,000Wh and up, sized around the fridge rather than the CPAP.
- Add solar only if your outages run past two days. A 100–200W panel replaces a humidifier-off night in a few hours of decent sun.
What not to buy: a whole-home battery justified by the CPAP alone. If you want home backup, buy it for the house; a CPAP is a rounding error on that decision and should not be the argument that sells it to you. And if your therapy is something you cannot safely skip, raise the sizing question with whoever supplies your equipment, since some machines have their own approved battery accessories.
What a CPAP costs to run per year
At a US average residential rate of roughly 17 cents per kilowatt-hour:
- Humidifier off, 30W for eight hours a night: about 88 kWh, or $15 a year
- Humidifier on at a moderate setting, 70W: about 204 kWh, or $35 a year
- Humidifier and heated hose on high, 90W: about 263 kWh, or $45 a year
- Left plugged in and idle during the day: about 12 kWh, or $2 a year
Even the worst case is under fifty dollars, which is the useful conclusion: running cost is not a reason to change anything about how you use the machine. Unplugging it during the day saves two dollars a year and buys you a chance to forget to plug it back in. Turn the humidifier off when you are on battery and leave it alone the rest of the time.
For scale, the machine costs roughly a fifth of what the refrigerator beside it does. If the electricity bill is the real problem, the CPAP is not where the money is going.
Frequently asked questions
How many watts does a CPAP machine use per hour?
Watts are already a rate, so the figure you want is watt-hours. A CPAP uses 25–40 watt-hours per hour with the humidifier off and 50–95 with it on. Over a standard eight-hour night that is 200–320Wh without humidification and 400–760Wh with it, depending on your humidity setting and room temperature.
Will a 300Wh power station run a CPAP all night?
Usually not, despite being widely recommended for it. After inverter losses and the inverter’s own idle draw, 300Wh gives roughly six and a half hours at 30W, which is short of a full night, and about three hours with the humidifier on. Treat 500Wh as the minimum for one reliable night with humidification switched off.
What size inverter do I need for a CPAP machine?
Far less than you would expect. A CPAP peaks at 80–110W and has no motor surge, so 150W of continuous pure sine output is technically enough. In practice the inverter rating is never the limiting factor — buy for watt-hours of capacity and the output rating takes care of itself. Avoid modified sine wave inverters.
Does turning off the humidifier save much battery?
Yes, and it is the single most effective thing you can do. The heater plate draws 50–85W while it cycles, against 25–40W for the blower alone. Switching humidification off roughly doubles your runtime, and can more than triple it if you were running a heated hose on a high setting in a cold room.
Can I run a CPAP from a 12V battery?
Yes, using the regulated DC cable your machine’s manufacturer sells for it, which skips the inverter and gains you 25–30% more runtime. At 30W the draw is about 2.5 amps at 12V. Humidification generally will not run from DC on most machines. Do not substitute a generic car adapter for the proper cable.
How much does it cost to run a CPAP machine per night?
Between four and eleven cents a night at 17 cents per kilowatt-hour, depending on whether the humidifier is running. Across a year that is roughly $15 with humidification off and $35–45 with it on high. It is one of the cheapest continuously used appliances in a typical bedroom.
Is a power station or a generator better for CPAP backup?
A power station, clearly. The load is small enough that a battery covers several nights, and a battery runs silently indoors with no fuel and nothing to start at three in the morning. A generator only wins on multi-day outages with heavy loads. Our comparison of the two covers where that crossover sits.
Next step. Measure one night with the humidifier off, divide the watt-hours by 0.85, and you have your minimum capacity. Then take that number to the finder and ignore every unit whose headline spec is an output rating rather than a capacity.