How Long Will a Power Station Run a Chest Freezer?

The numbers

A chest freezer is the most efficient cold appliance in an American house. The lid opens upward, so the cold air stays in the box instead of falling out onto the floor like it does with an upright.

Typical figures for modern US units. An older freezer from the 1990s can use double this. The EnergyGuide label gives your model's annual kWh — divide by 365.

The compressor pulls roughly 130 watts while it runs, but it only runs about a quarter to a third of the time. That duty cycle is what makes the runtime long. Multiply 130W by a 30% duty cycle and you get an average of about 40 watts — which is why a 1,000Wh battery goes 20 hours, not 7.

Surge is the other number. Expect the compressor to spike to somewhere around 600–1,000 watts for a fraction of a second on each start. Any unit with a 1,000W inverter or better handles it. Anything under 600W will trip, which is the same trap described in Why Does My Fridge Trip the Power Station?.

The trick that turns 20 hours into four days

Do not leave the freezer plugged in.

A full chest freezer holds its temperature for about 48 hours with the lid shut and nothing running. That is free cold, and you are wasting battery by fighting for it.

Instead: run the freezer in short bursts. Plug it in for about two hours, let the compressor pull the temperature back down, then unplug it and leave the lid closed. Repeat every twelve hours or so.

Two hours of runtime a day costs you roughly 260Wh. A 1,000Wh unit therefore covers close to four days of freezer, instead of not quite one.

This works because you are not trying to keep the freezer at -10°F. You are trying to keep it under 0°F, and the thermal mass of the frozen food does most of that work for you.

Do the free things first

Before you spend anything on backup power for a freezer:

Fill the empty space. A full freezer holds cold vastly longer than a half-empty one. Jugs of water, filled three-quarters and frozen, cost nothing and turn a half-full freezer into a full one. Do this now, not during the outage.

Do not open it. Every lid lift costs you hours. Decide what you need before you open it, then take everything at once.

Put a thermometer in it. A $10 freezer thermometer tells you whether the food is still safe. Without one you are guessing, and guessing about frozen meat is how people get sick. The USDA line is that food which still has ice crystals and is at or below 40°F can be refrozen.

We go further into this in How Long Will a Freezer Stay Cold Without Power?.

What to buy

A 500Wh unit with a 1,000W+ inverter is genuinely enough if you use the burst method. Two days of freezer protection, and it is the cheapest honest answer here.

A 1,000Wh unit is what we would actually buy, because it also covers the fridge, the phones and the router — and the fridge is the appliance with the real food value in it. See Best Solar Generators Under $1,000.

Add a 100W panel if you live somewhere with multi-day outages. A freezer's daily need in burst mode is small enough that one panel genuinely keeps up in summer sun.

Do not buy a 2,000Wh+ unit purely for a freezer. The freezer does not need it, and if you have the budget you should be thinking about the whole house, not one appliance.

The upright freezer footnote

Everything above assumes a chest freezer. An upright freezer loses cold every time the door opens, holds temperature about half as long unpowered, and runs a longer duty cycle. Take the runtimes above and cut them by roughly a third.

If you are buying a freezer and outages are a concern, buy the chest. It is the more resilient appliance by a wide margin.

The short version

• A 15 cu ft chest freezer averages about 40 watts once you account for duty cycle.
• A 1,000Wh unit runs it continuously for around 20 hours.
• Run it in two-hour bursts twice a day instead, and the same battery covers three to four days.
• Fill empty space with frozen water jugs before the season starts. It costs nothing and doubles your unpowered hold time.
• 1,000W inverter minimum, for the compressor's startup surge.