I believe ruminating on worst-case scenarios is often unproductive, but I also was a Boy Scout and the motto “Be Prepared” is an indelible part of my psyche. One of the best ways to “be prepared” for any kind of emergency is to have extra food stored in your freezer. However, freezers require power, and if you lose power your food will eventually thaw out. That’s why it’s worth knowing how long you can expect your freezer to stay cold in the event you lose power for long periods of time.
Luckily, Matthias Wandel, an engineer and professional woodworker from Canada, has done the hard work for us.
After purchasing a new, 14-cubic foot stand-up freezer, Wandel was curious how long food would remain frozen in the appliance after losing power. So, he rigged up a TP-LINK HS110 smart plug to track how much power the freezer consumes while plugged in to maintain it’s normal temperature, and Raspberry Pi mini PCs equipped with temperature sensors to track the internal coldness of the freezer when it was unplugged.
Wandel ran multiple experiments with varied amounts of food in the freezer for each. He also ran separate tests to see how much coldness was lost by opening the freezer door when it was empty, versus when it was full (you can download all the data from Wandel’s website).
How to keep your freezer cold as long as possible after losing power
Wandel’s data suggests the average full-length, stand-up freezer has between 18-36 hours after losing power until the freezer is no longer cold. That leaves most people with around one day before everything in your freezer is thawed.
The specific time will vary for everyone, obviously, but there are ways to maximize your freezer’s storage and location to make sure your food stays frozen as long as possible:
(Note: These figures are for full-length upright freezers. Wandel notes that chest freezers stay colder longer and more efficiently, even after opening them since the cold air can’t “fall out.”)
Don’t open the door, and if you do, make it quick. Every five seconds the door is open cuts about 7-14 minutes from the total thaw time, depending on how much food is stored.
The amount of food in the freezer impacts how long it all stays frozen. A densely-packed freezer stays cold nearly twice as long as one with less food and more open space, according to Wandel’s data.
The type of food also affects thaw time; small items without much water thaw quicker, while bigger items or food with lots of water thaw slower and help maintain the internal temperature. Prioritize large items with high water content like frozen meat, fruits, vegetables, and even bags or blocks of ice if there’s lots of extra space.
Room temperature will affect the thaw time quite a bit, so keep your freezer in a cold room, if possible. A warm room could speed up thaw times by about 25%.