Washing machines: How we test washing machines

How Which? puts washing machines to the test

The Which? test program for washing machines includes more than 300 tests on washing, rinsing, convenience issues and noise. We go to great lengths to design thorough and rigorous tests. For example, we enlist the help of Tomahawk the husky to test washing machines that have a 'refresh' cycle, measuring how well this removes dog odour from Tomahawk’s bedding.

You can see the differences between a good and bad washing machine and find out what it takes to become a Which? Best Buy in our video:

Washing machine cleaning

For cleaning, we test how each washing machine copes with shifting tough stains such as olive oil, grease, ink and cosmetics from a specially prepared cloth that’s put into the drum with T-shirts, sheets and other items.

After the wash is finished, we measure how much light is reflected from stains on the special cloth using a spectral photometer, so we can work out exactly how much of the stain has been removed.  

Rating washing machine noise

We use a panel of five experts to test how noisy washing machines are during their wash and spin cycles.

The Which? experts don't just look for how noisy a washing machine is, but also rate how intrusive and annoying the sound is.

Rinse test for washing machines

To measure how well each washing machine removes detergent during the rinse 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 2800rpm, 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 the alkalinity of tap water used in the wash. Detergent is alkaline, so the greater the increase, the poorer the washing machine is at rinsing.

For many washing machines we test, rinsing is an Achilles heel – there are only a few that produce good results on different wash programs.

Washing machine energy use

We don't just take a manufacturer's word for it when they say their washing machines are energy efficient. We run our own tests to calculate how much water and energy each machine uses, and work out how much you would pay to use each machine on the main cotton wash four times a week for a year.

Washing machine program choice

The Which? tests are designed to mimic the use of a washing machine in the home. By consulting our members, we've been able to build up a picture of how most people use their washing machine.

Though many washing machines include 15 or more wash programs, we know in reality most people stick to using the main cotton wash, the short program and the easy-care wash.

Each program is chosen in agreement with our independent lab testers after careful consideration of the controls and the manufacturers’ instructions, so we can be sure we accurately reflect the performance of washing machines.

The criteria we use are based on our experience of testing hundreds of washing machines each year.

Modern washing detergents enable most people to wash at 40ºC for almost all washes, so we only test at this temperature because this helps to protect the environment by reducing the amount of energy and water used by doing the washing.

We currently do a full load wash and the main easy-care cycle at 40ºC.

Our husky helps us test how well washing machines remove odours.

Washing machines special features

Often washing machines come with interesting or innovative new programs and features that we can test out in our lab. These can include express programs for cleaning clothes quickly; 'refresh' programs which claim to remove odours or freshen-up dry-clean clothes without water; and eco programs that claim to use less water and energy.

To test refresh programs, we call in the help of our canine friend Tomahawk the husky. We use woolly jumpers that Tomahawk has slept on for eight hours to see how well these programs remove his scent.

New vs old tests of washing machine

Some washing machine reviews have a note showing they were tested using our previous test program. That’s because we changed our testing in late 2007. Though you can generally compare older results with the latest washing machines we’ve tested, the results don't directly correspond.

However, each score still gives a good indication of the overall performance of a washing machine.

The biggest change is in the types of stains we use to measure the cleaning ability of the washing machines machines. We've replaced our old stains − including blood and chocolate − with soils that our research shows are commonly found in household loads. 

The new stains – including milk, grease, ink and olive oil – provide a good challenge for modern wash programs.

The number of programs we test regularly has changed, too. Between 2004 and 2007, fewer than 2% of machines tested have produced a poor short wash result. So we've stopped testing the short wash on every machine and instead focused on increasing the number of washing machines we can test.

See also our reports on washing machine brands and how to use your machine.

Trial Which? today to find out which washing machines we rated as Best Buys, or log in if you already have member access.