Chest freezer backup planning

A chest freezer is not a refrigerator with a different door. It often cycles less in a cool room, and a full cabinet keeps its cold longer when the lid stays shut. This site does not publish a typical chest-freezer wattage, because a made-up “typical” number would be a guess. Use the EnergyGuide yearly kWh on that freezer, or a meter on that freezer.

The closed-lid hold time in federal outage guidance is about food that is already frozen. It is not a battery runtime. A half-full freezer is described as holding temperature for less time than a full one if the door stays closed. Running the freezer from a battery is a separate plan: the compressor has to start, and the average draw has to fit the watt-hours.

Duty cycle is the honest extra input

If you know running watts while the compressor is on, and you have watched how often it runs, use duty-cycle mode. Average watts equal running watts times the fraction of time it runs. A duty cycle of 0.25 is an estimate you can revisit when the garage heats up. It is still not startup watts. If you do not know the startup figure, the calculator will not confirm that the battery can start the compressor.

Arithmetic only: half of the 500 kWh example

The 500 kWh refrigerator example averages 57.0776 W. Half of that average is 28.5388 W. This is not a measured freezer. It only shows the shape of the formula. At that lower average, a 2,048 Wh capacity plans for 40.7 hours, and 48 hours would need 2,418.1 Wh. Idle watts keep the relationship from being a perfect halving. Your label will not match this row unless the math happens to land there.

Enter the real label in the calculator. Read how to use the EnergyGuide number and the food-safety limits.