Cordless vacuum: where does that suction actually come from?

Cordless vacuums are sold on big numbers that rarely measure the same thing. Here is what sits underneath and what to look at.

Three numbers that get mixed up

Watts is power drawn. It says how much current the motor pulls, not how much comes out at the nozzle. An efficient motor with a good air path can suck harder on fewer watts.

Pascals (Pa) is suction pressure. This is the number that matters for dirt stuck in carpet. Around 15,000 Pa is fine for a stick vacuum, above that it gets serious.

Airflow in litres per second determines how fast you lift loose dust from a hard floor. For laminate and tiles this counts more than pascals.

If the packaging only shows watts, it is usually because the other two are not impressive.

The runtime on the box

That is measured on the lowest setting with the plain nozzle and no powered brush. Switch to turbo and forty minutes quickly becomes eight. Not deception, but worth knowing before you plan to do a whole house in one go.

Practical: do hard floors on the lowest setting and save the highest for carpet and the edge of the sofa.

Where it goes wrong in practice

• Filter. A clogged filter halves suction without you noticing, because it happens gradually. Tapping it out every few sessions and washing it monthly helps more than a pricier machine.
• Hair around the brush. With long hair or a pet this is a problem within a month. Check whether the brush roll comes out without tools.
• Weight and balance. A machine with the battery on top feels lighter on the floor but heavier held up for the ceiling.
• Emptying. A bin you empty over the rubbish with one button beats a system where your hand ends up in the dust.

Our cordless vacuum with LED light has a light in the nozzle, which is less gimmicky than it sounds: under the sofa and along skirting boards you only see how much is there with light on it.

Replacement down the line

The battery gives up first, usually after three to five years. Ask before buying whether it can be replaced separately. If not, you are effectively buying an appliance with an expiry date.