What Size Power Station for a CPAP and Refrigerator?
Size one battery for overnight CPAP use plus cycling refrigerator demand during an outage.
Combining a medical load with refrigeration changes the sizing problem because CPAP can be predictable overnight while refrigerator energy is spread across the full day.
A CPAP plus refrigerator is a mixed continuous/cycling load. Add the CPAP’s overnight watt-hours to the refrigerator’s measured daily energy, then divide by usable battery fraction. Humidification/heated tubing can materially increase CPAP consumption.
What matters
- Prioritize the CPAP energy requirement first.
- Use measured refrigerator daily kWh.
- Humidifier and heated tubing can materially increase CPAP power.
- Leave reserve rather than planning to zero battery.
Decision factors that change the answer
CPAP configuration
Humidifiers and heated hoses can raise overnight energy use significantly.
Refrigerator cycling
Use measured kWh/day rather than multiplying running watts by 24.
Shared overnight demand
Both loads may run at the same time, so inverter output still matters.
Extra-night reserve
For therapy continuity, plan beyond the minimum single-night calculation.
How to size it
- Estimate overnight CPAP Wh.
- Add refrigerator daily Wh for the outage window.
- Apply conversion losses and reserve.
- Check refrigerator startup output.
A CPAP averaging 40W for eight hours adds about 320Wh before losses; add that to the refrigerator’s measured daily energy budget.
Worked example
A refrigerator using 1.2kWh/day plus a CPAP using 400Wh/night totals about 1.6kWh/day. At 85% usable AC energy, a 2kWh-class station is roughly one day of capacity before reserve.
Common buying mistakes
- Using CPAP running watts without considering humidification.
- Assuming refrigerator compressor watts run continuously.
- Leaving no medical reserve.
Medical loads should drive reserve policy; use the outage planner to combine both loads explicitly.
Check the underlying numbers
Use these site resources to replace generic assumptions with your own load or the source-linked data behind this guide.
Use the numbers before choosing a model
Start with your load list. The battery needs enough watt-hours for the desired runtime and enough continuous/surge watts to operate the appliances at the same time. Then check whether your recharge method can replace the energy you expect to consume.
For outage planning, we recommend keeping reserve capacity instead of designing a system that reaches 0% at the end of the forecasted outage.
Next step
Estimate battery runtime → or Build a critical-load energy budget →.