How we test freezers

Which? Best Buys exist to showcase the very best products you can buy. Find out what you can expect from a Best Buy freezer. 

Our rigorous tests help Which? members to spend their money wisely. From temperature accuracy to energy efficiency, we test every aspect of a freezer's design and performance to make sure you have all the information you need to choose your perfect model.

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Why our freezer tests are different

When reviewing freezers in our test lab, each model is given an overall percentage score calculated purely on measurements and ratings we generate ourselves. 

We don't accept free products from brands, either. At Which?, we buy every appliance that we score.

What are Which? Best Buy, Don't Buy, Eco Buy and Great Value freezers?

We give Best Buys to freezers that impress the most in our tests. Freezers that score 75% or more are Best Buys and come with a firm overall recommendation, although you should still read our reviews to check for any factors that might impact your buying decision. Meanwhile, freezers that score 45% or below are Don’t Buy models to avoid.

Best Buy freezers

Best Buy freezers typically tick the most important boxes. They're quick to cool down, stick closely to their set temperature and don't use too much energy.

Great Value freezers

How much buyers are willing to spend on a freezer varies, so that’s where our Great Value recommendation comes in.

Great Value models do pretty well in our tests – scoring 65% or more – and they still score three stars or better for chilling power and four stars or more for energy efficiency. So they cost less to run than lower-scoring models and will keep your food safely frozen. They're also at least 20% cheaper than the average price for that type of product in our tests.

Great Value models are the ones to go for if you’re looking for a bargain. Some Great Value models may also score well enough to be Best Buys.

Eco Buy freezers

If you want to make the most sustainable choice when you next buy a freezer, go for an Eco Buy model. 

Eco Buy freezers will have a lower impact on the environment over their lifetimes than other freezers.

We calculate this in two ways: how reliable and therefore long-lasting it's likely to be – so you don't have to repair or replace it as often – and how energy efficient it is.

To become an Eco Buy, a freezer must have:

• a total test score of at least 75%
• five stars for energy efficiency
• four stars and above for cooling power
• not come from a brand that gets a poor longevity rating in our annual consumer surveys.

Only between 5% and 10% of freezers are sustainable enough to be Eco Buys. To find out which qualify, head to our freezer reviews and use the Eco Buy filter.

Don't Buy freezers

Don't Buy freezers fall down in important areas. They may take ages to cool down and then veer away from the temperature they're set at.

How is the Which? score calculated?

Weightings and star ratings

• 35% – freezing power
• 22% – energy efficiency
• 12% – convenience, including ease of use, ease of cleaning and noise
• 10% – accuracy of recommended thermostat setting
• 10% – performance at the optimum setting
• 6% – ability to keep contents frozen in the event of a power cut
• 5% – ability to keep contents frozen in a hot room.

Our key testing criteria

Below are our key testing categories and how we evaluate each one.

Freezing power

Key question: how quickly will the freezer freeze my food?

Our rigorous lab tests are designed to reveal how a freezer will behave in your kitchen. 

To do this, we set the room temperature to 23°C and part-fill the appliance with gel packs to simulate food. Once these have cooled, we add more even more – roughly equivalent in size to what you’d buy during a top-up shop for fresh food – and record the time taken for these packs to cool.

The best freezers will freeze your food in a matter of hours, keeping it fresh. On the other hand, the worst models we've seen struggle to complete our tests during two whole days of testing.

Freezing power makes up 35% of the total freezer score.

Energy efficiency

Key question: how much will the freezer add to my energy bills?

Never switch off your freezer to save electricity – you risk food poisoning and higher bills as your appliance will use more energy when trying to get its temperature back down. Buying a model that is energy efficient for its size is crucial.

Our energy testing was updated in 2023 to make it even more stringent, in view of the cost of living and climate crisis. Therefore, the results of freezers published before and after September 2023 are not 100% comparable. However, the scores of the older models we've tested still give a very good indication of how a freezer will perform in your kitchen.

Several tests go into our new energy measurements, including:

• How much energy each freezer uses to keep food cold, measured over 24 hours. During this time, our experts open and close the freezer door several times to replicate how you'd use your freezer in real life: opening it a few times a day to take food out and/or put shopping in.
• How much energy each freezer uses to freeze fresh food.

We then calculate what this is likely to add to your energy bill. To see whether a freezer is cheap to run for its size, we also rate its energy use against the amount of useable storage space it offers – you can see the results on the technical specification tab for each freezer review.

Energy use accounts for 22% of the overall freezer score. 

Convenience

Ease of use and cleaning

Key question: how easy is the freezer to use and clean?

Some freezers are easier to use than others, and a seemingly minor flaw will soon become a major issue after you’ve experienced it on a daily basis. We rate ease of use, looking at key aspects such as how sturdy the shelves and drawers are and how smoothly the drawers slide in and out.

We also spray cherry juice inside each freezer and let it dry to a sticky mess. Then, our experts rate how easy it is to wipe away, and see how likely food and drink spills are to seep into hard-to-reach spots. The best freezers are a breeze to keep clean, while the worst have areas that can trap food spills and bacteria.

Quietness

Key question: how noisy will the freezer be in my kitchen?

How much noise a freezer makes is particularly important for anyone working or studying from home in a kitchen, or living in a studio flat. 

Every freezer we test is assessed in our lab for noise in specially designed sound chambers. It's possible for a freezer to be quiet most of the time, but then make irritating noises when the compressor switches on. To check this, we assess sound quality over a prolonged period of time, rather than just taking a one-off decibel measurement.

Convenience contributes 12% to the total test score.

Accuracy of thermostat

Key question: can you trust the freezer thermostat?

Your freezer's instruction manual will let you know what setting to set the appliance to. But unless you check with a thermometer, there's no way of knowing if the recommended setting is reaching the ideal temperature. 

We check how accurate the thermostat is – whether setting the freezer to the manufacturer-recommended setting actually brings it down to the desired temperature. We follow the manufacturer's instructions to set the thermostat and then record the temperature of gel packs in the freezer compartment.

The best freezers reach the ideal temperature, but the worst are way off – and following the manufacturer's instructions means you're storing food at a warmer temperature than you think. As a result, your food could go off more quickly and potentially be unsafe.

The accuracy of the recommended thermostat setting accounts for 10% of the total test score.

Performance on the optimum setting

Key question: how well does a freezer perform when it's set to the optimum setting

Not all freezers reach the temperatures claimed by their thermostat. Therefore, we set every model to the optimum or ideal setting: we make sure it's set to -18°C, and then we test its ability to freeze food under those conditions.

Performance on the optimum setting accounts for 10% of the total test score.

Ability to keep contents frozen in a power cut

Key question: will the freezer keep my food safely frozen in a power cut?

To simulate a power cut, we measure how long it takes for our test loads in the freezer to rise from a starting temperature of -17°C to -9°C and -7°C in a 23°C room.

Note that you should never turn off your freezer to save money – you'll be putting your food (and health) at risk and potentially causing your energy bills to shoot up as your appliance attempts to re-freeze your food.

Temperature stability in a power cut makes up 6% of the score for a freezer. 

Ability to keep contents frozen in a hot room

Key question: will the freezer keep my food safely frozen in a hot environment?

A freezer needs to keep your food frozen around the clock, even when your kitchen heats up and cools down. An evenly cool environment is essential for preventing harmful bacteria from growing and stopping food from spoiling faster than necessary.

With that in mind, we raise the temperature in our test chamber to 35°C, replicating a heat wave, to see whether the gel packs inside remain safely frozen. 

Temperature stability in warm rooms makes up for 5% of the score for a freezer. 

Which? freezer testing changes

We constantly improve our freezer tests to guarantee only the top-scoring models are Which? Best Buys. This means that newer freezers have been tested and rated in a slightly different way to older models, but you can still use the overall test scores to compare one freezer with another.

Our testing program covering freezers has been updated several times over the years. You can see when each appliance was tested under the ‘Technical specification’ tab in each review.

Freezer running costs

We take into account the amount of power a freezer uses to freeze fresh food to give you a more accurate idea of how each model might impact on your energy bills. Because our energy calculations are now more accurate, running costs for models tested before and after 2015 shouldn’t be directly compared.

Want to see which freezers come top in our tests? Check out the best freezers.