What does frost free mean and do I need it?

A static freezer makes the inside of its walls cold, so moisture from the air and from the food freezes onto those walls as frost. A frost free freezer makes one hidden surface cold instead, blows air over it, and periodically warms that surface just enough to melt the accumulated frost, which drains away out of the cabinet. The whole difference in behaviour follows from that one design change.

Step by step

1. Understand what is actually happening in a static freezer.The cooling coils are bonded into the walls and shelves. Whenever the door opens, warm humid room air enters, meets those surfaces and deposits its moisture as frost. Over months that builds into a layer that insulates the walls and costs you space and efficiency.
2. Understand what a frost free model does differently.The evaporator sits in a separate compartment, usually behind the rear panel. A fan draws cabinet air over it and back into the compartment. All the frost forms on that hidden evaporator, and a small heater runs for a few minutes several times a day to melt it into a drain.
3. Weigh the space you get back against the space you lose.You never lose litres to ice, which is the gain. Against that, the evaporator housing and ducting occupy real volume, so a frost free appliance is typically smaller inside than a static one of the same external size.
4. Weigh the running cost.The fan runs and the defrost heater runs. Both use electricity, so frost free generally consumes somewhat more than an equivalent static model. Against that, a static freezer with two centimetres of ice on the walls is running far less efficiently than it should, and most of them do.
5. Account for the dry air.Constantly circulating air dehydrates anything not properly sealed. Freezer burn — the pale, leathery patches on frozen meat — happens faster in a frost free freezer. Wrap tightly, use bags with the air pressed out, and this is a non-issue.
6. Account for the noise.A frost free appliance has a fan, so it makes a low continuous whoosh that a static one does not, plus occasional cracking and trickling during a defrost cycle. In a kitchen it is unremarkable; next to a bedroom wall it is worth thinking about.
7. Decide on your actual behaviour.If you have defrosted a freezer once in the last three years and it currently has ice in it, buy frost free — the appliance is doing the job you were not going to do. If you keep on top of it, run a chest freezer, or want the quietest and cheapest option, static is genuinely fine.
8. Know that frost free still ices up when something is wrong.Ice inside a frost free freezer is a fault, not neglect: a door left ajar, a failed door seal, a blocked defrost drain or a failed defrost heater. It means something to fix rather than something to scrape.

Tips

• Auto-defrost in a fridge compartment is not the same thing as frost free. Fridges above freezing defrost naturally between compressor cycles; the water runs to the drain hole at the back. Almost every fridge has done this for decades.
• Some appliances are frost free in the freezer and auto-defrost in the fridge, which is the arrangement that gives most of the benefit for least of the cost.
• A frost free freezer full of tightly packed food runs more efficiently and is less affected by the circulating air, because there is less air to circulate.

Common mistakes

• Assuming frost free means no maintenance at all — The defrost drain can block with debris and refreeze, at which point water pools and ice forms in the base of the cabinet. It is a rare job but it is not a never job.
• Storing food unwrapped or loosely covered in a frost free freezer — The moving air is drying air. Ice cream in an opened tub, bread in a loose bag and unwrapped meat all suffer noticeably faster than they would in a static freezer.

Questions people ask