CPAP & Medical Device Generator Calculator
Data reviewed ·how we calculate
Powering a CPAP through an outage is not a comfort question — for many users it is a health necessity, and for other medical devices (oxygen concentrators, home dialysis, powered mobility) the stakes are higher still. The electrical math is easy: a CPAP alone draws 30–60W, around 150W with a heated humidifier. The planning is the hard part, which is why this page leads with a disclaimer most generator sites skip: talk to your device manufacturer and your physician first, and consider a medical-grade battery backup as the first line, with the generator as the recharger.
Size a generator for this load
Computed on typical values; ranges shown below. 25% headroom applied.
How to size it step by step
Confirm the device’s real draw from its power supply label or manual — medical device wattages vary by model and setting far more than kitchen appliances do.
Decide the humidifier question: turning the heated humidifier off cuts a CPAP from ~150W to ~40W, tripling battery runtime. Many users accept a passover (unheated) humidifier during outages.
Prefer a battery-first setup: a 300–500Wh power station runs a humidifier-off CPAP through a full night silently and indoors. Size the generator to recharge the battery by day.
If the generator is the direct source, any 2,000W inverter covers the load with enormous margin — the constraints are placement (outdoors, 20+ ft away, never indoors) and clean inverter output, not watts.
Pro tips
- Check your nameplate first — every figure on this page is a planning estimate, and the label on your specific unit beats any chart.
- Practice the outage before it happens: run the CPAP from your chosen backup for one full night while utility power is fine, so surprises surface on a night that doesn’t matter.
- Keep a 12V adapter for your CPAP in the kit — most models sell one, and a car or deep-cycle battery becomes a legitimate emergency fallback.
- If anyone in the home is on powered medical equipment, tell your utility now: medical-needs registries get priority restoration calls in many service areas.
The data behind this calculator
| Figure | Value | Source |
|---|---|---|
| CPAP, humidifier off | 30–60W, 40W typical | ResMed/Philips Respironics power specifications |
| CPAP with heated humidifier | 90–200W, 150W typical | ResMed/Philips Respironics power specifications |
| Portable oxygen concentrator | 100–600W depending on model and setting | Inogen/Philips manufacturer specifications — verify YOUR model’s nameplate |
| Runtime on a 500Wh battery station (CPAP, no humidifier) | roughly one full night (8–10 h) | Arithmetic: 500Wh ÷ 40–50W, less inverter losses |
Duty cycle: With the heated humidifier on, the heater cycles through the night, so average draw sits below the peak figure — but size for the peak, since the heater and blower run together.
CPAP & medical devices generator questions, answered
What size generator do I need to run a CPAP machine?
Electrically, almost any: a CPAP draws 30–60W with the humidifier off — call it 40W typical, or 50W with the 25% headroom applied — which the smallest 2,000W inverter class covers roughly forty times over. The real questions are about reliability and safety, not watts: what happens if the generator stalls while you sleep, and where the generator sits (outdoors only, never in a garage or near a window). That is why a battery backup is usually the better first line.
Is a battery backup better than a generator for a CPAP?
For the overnight hours, usually yes. A 300–500Wh battery power station runs a humidifier-off CPAP all night, sits silently at the bedside, and cannot produce carbon monoxide. Its weakness is capacity across multi-day outages — which is exactly what a small generator fixes by recharging it each day. Manufacturer battery kits (ResMed Power Station, etc.) are the cleanest option; consult your device’s documentation for approved supplies.
Should I run the heated humidifier on backup power?
It is the first thing to sacrifice. The heater is 70–80% of the total draw: roughly 150W with it, 40W without. On a generator the difference is trivial; on a battery it is the difference between one night and three. Most CPAPs can run a passover humidifier (water chamber in place, heat off), which preserves some moisture without the wattage.
Can I run an oxygen concentrator on a portable generator?
Only plan this with your equipment provider and physician involved. Concentrators draw far more than CPAPs — 100–600W depending on model and flow setting — and are genuinely life-critical, so the backup plan needs to be engineered, not improvised: confirmed nameplate draw, an inverter generator or manufacturer-approved power source, a fallback oxygen supply, and enrollment in your utility’s medical-baseline/priority-restoration program.
Does a CPAP need a pure sine wave inverter generator?
Manufacturers generally specify clean power, and inverter generators provide it — their low-distortion sine output is equivalent to utility power. A conventional contractor generator’s rougher waveform may still work but is outside many devices’ specifications and can stress the power supply. Given that CPAP-sized inverter generators are the cheapest class on the market, clean power is the easy choice here.
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