Battery & storage
Enter your freezer's wattage and how many days you want it running during an outage. Get a battery size just for this one appliance.
How it works
Step 1
Check the nameplate for an exact figure, or use a typical range by freezer type, similar to the approach in the refrigerator backup tool.
Step 2
A well-stocked freezer stays cold for 48 hours or more even without power, giving some natural buffer beyond the battery figure.
Step 3
The critical loads calculator adds a freezer alongside a refrigerator and other essentials into one battery size.
This calculator assumes the freezer runs continuously at its rated wattage, which overstates real energy use since compressors cycle on and off rather than running nonstop, similar to how a refrigerator behaves, a duty-cycle pattern ENERGY STAR's appliance efficiency database accounts for in its own energy use ratings. In practice, actual daily energy use is often somewhat lower than the continuous-running math suggests, making this a safe upper bound rather than a precise prediction. The refrigerator backup tool uses the same conservative approach for that related appliance.
Frozen food itself acts as thermal mass, holding cold and resisting warming even when the freezer loses power entirely. A full, unopened chest or upright freezer typically keeps food safely frozen for about 48 hours according to FoodSafety.gov's power outage guidance, while a half-full freezer holds safely for roughly 24 hours. This means a battery sized for slightly less than your full desired duration may still be adequate in practice, since the freezer's own thermal mass extends the safe window somewhat.
If you're backing up both appliances during an outage, which is common, simply add their running wattages together and use the combined figure, since both typically run simultaneously rather than at separate times. The critical loads calculator handles this combination automatically alongside other essential circuits like lighting and internet, and the hybrid inverter sizing calculator in our Inverters & Equipment category confirms your inverter can handle both compressors' combined startup surge.
If you're planning a full critical loads system rather than just this one appliance, the backup runtime estimator combines the freezer with everything else you want backed up into a single battery size. If you're financing a battery system around this and other essential loads, the monthly budget fit calculator in our Financing category helps confirm affordability.
Questions
A typical freezer drawing 200 running watts needs about 17.4 kWh of nameplate battery capacity to run continuously for 3 full days. A well-stocked, well-insulated freezer often stays safely cold for 48 hours or more even without any power at all, giving some buffer beyond the battery figure.
Yes, a full freezer holds cold significantly longer than a mostly empty one, since the frozen contents themselves act as thermal mass that resists warming. This matters both for battery backup planning and for how long food stays safe if the freezer loses power entirely.
Yes, if you're backing up both appliances, add their wattages together and use a combined figure, since they'll typically run at overlapping times. The critical loads only calculator handles this combination directly alongside other essentials.
A full, unopened chest or upright freezer typically keeps food safely frozen for about 48 hours, while a half-full freezer keeps food safe for roughly 24 hours, according to general food safety guidance. Keeping the door closed as much as possible extends this window.