The overall Which? test score is made up of the following star ratings, all determined by our rigorous lab tests.
How we test cottons cleaning
We challenge each machine we test to clean a range of stains, including tough-to-shift blood, grease, ink, milk, oil and rust. We place stained cloths in the drum, along with sheets and other items of clothing to test the 40°C cottons program. 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.
How we test quietness
We measure how much noise the machine makes during washing, spinning and drying. High scoring washer-dryers make the least noise during use.
How we test energy efficiency
We test how much energy the machine uses doing a load of laundry on a wash and dry cycle. Machines rated 4 stars cost around £21 less to run per year than those that are rated 2 stars, based on five loads of washing and four loads of drying a week.
How we test synthetics cleaning
We challenge each machine we test to clean a range of stains, including tough-to-shift blood, grease, ink, milk, oil and rust. We place stained cloths in the drum, along with sheets and other items of clothing to test the 40°C synthetics program. 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.
How we test spin drying
Clothes are weighed when they're dry and then again after the spin cycle to assess how much moisture is left in them after the spin dry. The more effective the spin dry, the easier it is for the machine to dry clothes quickly and efficiently.
How we test rinse
To assess the quality of the rinse we spin rinsed clothes in a super-fast spin dryer to extract any remaining water and test the alkalinity of this water, which is a good measure of how much detergent was left in the clothes during the rinse. This can be an important factor for people with sensitive skin.
How we test drying programs
We measure how long it takes to complete preselected programs, including cupboard drying where clothes are dry enough to be put away and synthetic fibres which can be damaged by high heat or overdrying.
How we test dryness of clothes
We measure how dry clothes are at the end of the programme. We do this by weighing them before and afterwards. This star rating applies for models tested after 2013: automatic washer-dryers should not over-dry clothes or leave clothes wet. Manual dryers that make you set the drying time yourself should have consistent drying results.
How we test drying evenness
The best models dry all items equally well, while others leave some items damp. We weigh all items in the drum before and after drying and measure the difference between the wettest and dryest clothes in the drum.
How we test water use
We measure how much water the machine uses to wash and dry clothes. The more stars a machine gets the more water-efficient it is, which can be particularly important if you're on a water meter. Water is used by most washer-dryers when drying to cool the condenser unit.
How we test ease of use
We test how easy it is to load the machine, use its control panel to program it, and assess how easy it is to clean the lint filters.
