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Updated: 12 Jul 2021

How we test washer-dryers

Which? tests washer-dryers more thoroughly than anyone else. Find out how we test to find the best washer-dryers and help you avoid the worst ones.
Matt Stevens

Each washer-dryer rated in our washer dryer reviews has been put through a series of independent tests in the Which? test labs. 

We wash and dry more than 1,300kg of laundry a year in our rigorous tests so you can be sure the ones we recommend really do live up to their claims.

Our reviews answer your most crucial questions about washer-dryers:

See our best washer-dryers to find out which models give top-class results.

How good is it at removing dirt and grime from clothes?

The best washer-dryers will leave your clothes sparkling clean and fresh, while the worst will make you wish you’d never pressed start.

To check how well a washer-dryer removes stains, we place a cloth splattered with chocolate, oil, blood and red wine marks in the drum, along with sheets and other dirty items of clothing.

We fill the drum with a mixed load that simulates the laundry of an everyday user, and test two wash programs three times over to ensure the accuracy of our results.

  • 40°C cottons program We fill the drum to 80% capacity with samples of stained cloth and mixed clothing, including shirts, jeans and towels, to imitate how you would typically fill your washer-dryer.
  • 40°C Easy care/synthetics program Synthetics wash programs have a capacity of around half the maximum of the washer-dryer, so we load the drum to 50% capacity with a mixture of man-made fibres such as polyester.

After the wash, we measure how much light is reflected off the cloth using a machine called a spectrophotometer, which measures the intensity of reflected light. The more light reflected, the better the machine is at removing stains.

Will this washer-dryer dry quickly and evenly?

The best washer-dryers will handle drying your clothes just as well as washing them. Unfortunately, our tests have found that all-too-often washer-dryers are let down by their standard of drying.

We measure how much time it takes to dry six loads of laundry on two program settings, and rate the washer-dryers based on the standard and evenness of their drying.

The cottons loads we test fill the drum to its maximum drying capacity, which is usually a little over half of the total wash capacity – so a 10kg capacity washer-dryer is likely to have a 6kg drying capacity.

As with wash capacity, the drying capacity for synthetics loads is around half that of cottons loads – so a washer-dryer with a 6kg drying capacity will dry a 3kg synthetics load in our tests.

Your time is precious, which is why we record how long washer-dryers take to dry your clothes and take the times into account in our overall drying ratings.

Our tests have found huge variations in how quickly washer-dryers can get your clothes dried. The quickest dryers can take as little as 25 minutes per kilo, and the slowest as much as 82 minutes per kilo – this means that the quickest dryers will take roughly two and a half hours to dry a cottons load, and the slowest could take more than eight hours.

Determining when clothes are ‘dry’ involves weighing them to see how much water they contain before and after the program.

We weigh individual items of clothing to work out how much water each contains. This can vary from 3% for a sheet to more than 20% for a pair of jeans or a towel. 

The variation between the different items tells us both how well-dried the clothes are, as well as how even the drying is.

Is the washer-dryer from a reliable brand?

However effective your washer-dryer may be, it will still let you down if it's prone to developing faults or breaking down.

To find out which brands are the most reliable, we survey thousands of washer-dryer owners every year about any faults or breakdowns they've experienced, and we use this data to calculate reliability ratings for each of the major brands. The higher the reliability rating, the more reliable that brand has proven to be, according to the experiences of owners.

A washer-dryer can only qualify as a Best Buy we recommend if, as well as the machine doing a great job, the brand scores at least three out of five stars for reliability, from our annual survey of owners. Alternatively, a product can also be a Best Buy if it does not score highly for reliability but instead has a free five-year warranty as standard.

Find out which washer-dryer brand came top in our most recent reliability survey.

We evaluate every machine's design and controls to assess how easy it is to use. Examples of some features our experts look for are listed below:

  • Indicator lights - We prefer large and bright lights that indicate when the filter needs cleaning, or a light inside the drum to assist with visibility when loading and unloading. Lights on the control panel should be accompanied by a clearly marked and self-explanatory label, which is visible from standing and sitting positions.
  • Loading and removing washing -We look for a wide drum opening and a door with a wide porthole that doesn’t have a fiddly handle and which opens to 180 degrees. You should also be able to load it easily from a standing or sitting position.
  • Detergent dispenser - This should be easy to open and close, with no sharp edges. It should require little force and dexterity to remove and replace for cleaning. It should also have clear labels to indicate which compartments are for detergent and fabric conditioner, and the maximum fill level.
  • Buttons and dials - We look for clearly marked, well-spaced protruding buttons and dials, with descriptions that are self explanatory and easy to read. They should also be easy to grip and turn or activate. Touch-sensitive buttons should not be too responsive, as this can cause you to change your setting by accident as you brush past your washer-dryer.

Different sizes, textures and shapes, as well as noises that indicate a button has been successfully selected, are helpful to people with visual impairments.

How much does a washer-dryer cost to run?

Washer-dryers can be far from cheap to run due to their dual functions, so we measure exactly how much water and energy each washer-dryer uses at the Which? test lab. The lower the amount of energy a washer-dryer uses, the lower your energy bills. 

We use our analysis to calculate estimates of how much each washer-dryer will add to your energy bills each year, so you can compare models on running costs as well as the purchase price. To help you know whether the energy costs are high or low for the product, we also provide an energy-efficiency star rating in our reviews.

Washer-dryers running costs

The chart below shows the highest and lowest yearly running costs we have measured in our tests for washer-dryers.

Based on all washer-dryer reviews currently live on which.co.uk and correct as of February 2020.

Will it make a lot of noise?

We also measure how much noise the machine makes, since there's no way for you to tell this in the shop. 

Some washer-dryers are so quiet you'd hardly know they're running, while others are so loud you'll need to move your conversation to the next room.

Are its rinse and spin cycles any good?


Detergent can be irritating to those with sensitive skin. To measure how well washer-dryers remove it during the rinsing cycle, we take freshly rinsed washing from the machine, just before the spin cycle, and spin it in a super-fast spin dryer.

This dryer spins at 2,800rpm, roughly twice as fast as a typical washing machine. After the spin, we collect water from the clothes and measure how alkaline it is compared with tap water. Detergent is very alkaline, so the greater the alkaline level, the poorer the machine is at rinsing.

Should I buy it?

Our in-depth washer-dryer tests assess everything from how clean they get your clothes to how much energy they guzzle and how easy (or not) they are to use. But because cleaning and drying power are so crucial, 65% of the overall test score we award to each washer-dryer is centred on these key functions. Below we reveal the full breakdown of how we weight washer-dryer test scores.

  • 50% Washing
  • 15% Drying 
  • 15% Ease of use and noise
  • 10% Energy efficiency
  • 5% Water usage
  • 5% Noise 

Washer-dryers have to achieve a score of 65% or more to earn our Best Buy recommendation. Washer-dryers that score 45% or less are marked as Don't Buy models we think you should avoid.