How we test carpet cleaners

If you decide to buy a carpet cleaner, rather than renting one, you'll want to make sure it's a decent model. 

At Which? we go to great lengths to test carpet cleaners rigorously so that you avoid buying a dud. We've found a number of mediocre and poor carpet cleaners that fail to clean carpets well - some costing hundreds of pounds. 

Our reviews will help you buy a carpet cleaner that cleans and dries carpets effectively, making your tired surfaces look sparkling again. 

Our independent lab tests focus on the most important qualities you'd expect in a good carpet cleaner, including:

• How clean will it leave tired and grimy carpets?
• Can it clean dried-on stains?
• How wet will it leave my carpets?
• Is the carpet cleaner quiet and easy to use?
• Should I buy it?

Only the models that impress us with their cleaning power join the ranks of our best carpet cleaners.

How clean does it leave tired, grimy carpets?

We test the cleaning power of each machine on three pieces of soiled carpet. Once the carpet has been cleaned and dried, we expertly assess the samples with a machine called a spectrometer (which measures brightness). This tells us how much dirt has been lifted from the carpets, and how much brighter and cleaner they look.

Marks are also deducted for uneven results, such as stripes being left along the carpet.

We also measure how close to the edge of the room a carpet washer can clean so that you get even results. Some models can clean right up to the edge, but others leave a large strip of grubby uncleaned carpet around the edge of a room - more than 7cm in one case.

The main picture at the top shows the difference between an uncleaned carpet on the left, a carpet cleaner that gets one star in our testing in the middle (the carpets are still dirty) and a carpet cleaner that gives a five-star clean - the carpet is left clean and refreshed.

Skip straight to our carpet cleaner reviews to find the top-scoring models we recommend.

What's the carpet cleaner like on dried-in stains?

Although they're not primarily designed for tackling tough stains, some carpet cleaners will come with special accessories for spot cleaning. And we always check how well each model copes with common spills that might be lurking in your carpets.

Carpet samples are stained with 10ml of red wine, coffee and mud, and left to dry for 24 hours. The carpet is then cleaned according to the carpet cleaner manufacturer's instructions and assessed to see how much of the stain has been removed.

Unfortunately, most aren't great at this job - you're usually better off using a carpet stain remover spray or spot cleaner - but our Best Buys are typically better than most.

How wet will the carpet cleaner leave my carpets?

It's not just about the washing - you'll want to avoid a carpet cleaner that leaves your floors waterlogged after the cleaning is done. Some models struggle to suck dirty water back up as they go, leaving you with a soggy and potentially mucky carpet.

To check how wet carpets are left after cleaning, we weigh carpet samples before cleaning is done and then again one hour, five hours and 24 hours after cleaning to see how much water they're still holding. The more stars a model gets in our drying test, the drier it will be after cleaning.

How quiet and easy to use is the carpet cleaner?

Cleaning carpets can be a slow business, so the last thing you want is to put up with a cumbersome, noisy or tricky model. We ask a panel of three experts to assess how noisy the carpet cleaner is - and whether the noise is particularly intrusive or irritating. 

When it comes to things such as weight, we don't just take the manufacturer's word for it - we check the credentials of each machine so you can compare them on a like-for-like basis, based on real-life scenarios.

• How far you can clean from the plug socket - we measure the length of the carpet cleaner's cord and nozzle so you know exactly how far you can get.
• How long you can clean for before topping up - we check how much water the tank can hold without leaking.
• How heavy it is - we weigh the machine when the water tank is empty and full, and note if you can remove the tanks to make lifting the machine easier.
• How easy or difficult it is to use - instructions are marked for their clarity and we rate what the machine is like to use - how easy it is to assemble, fill and empty the water tank, and push the cleaner around.

Should I buy it?

Each of the assessments described above goes part way to making up the overall test score, which is the percentage figure awarded to each carpet cleaner. This is weighted based on how important each test is. So carpet cleaning (cleaning mud and deep cleaning carpets) accounts for a large part of the score, as it's the machine's main function. The score is made up of:

• 70% Cleaning
• 15% Energy
• 10% Ease of Use
• 5% Noise

The cleaning score includes our stain removal and drying tests.

A model needs to score 80% or more to be considered a Best Buy carpet cleaner. Any that score below 45% are highlighted as Don't Buy carpet cleaners: these are so bad we think you should avoid them altogether.