Which vacuum cleaner filters can be washed, and how often do they need changing?

A vacuum's filters sit at two different points in the airflow and have two different jobs, which is why they are made of different things and looked after differently. The pre-motor filter sits between the bin or bag and the motor and catches whatever the bag or cyclone missed; it protects the motor and it is the one that loads fastest. The post-motor or exhaust filter sits after the motor and decides how clean the air leaving the machine is; it also catches carbon dust shed by the motor's brushes. Confusing the two is why people wash a filter that should have been replaced, or replace one that only needed a rinse.

What you'll need

• The machine's manual, or the model number to look it up
• Cold running water
• A spare set of filters, so you are not waiting 24 hours (optional)

Step by step

1. Find how many filters your machine has, and where.Almost all have a pre-motor filter behind or under the bin. Most also have an exhaust filter, often a disc or cassette at the back or base. Some cordless sticks have a third at the top of the bin. The manual lists them, and the model number finds the manual.
2. Identify each one by what it is made of.Open-cell foam or a felt-like sponge: washable. A rigid concertina of pleated white or blue paper-like media, usually in a plastic frame: not washable, replace. A fine mesh screen: washable. If it is labelled HEPA and pleated, treat it as replace-only unless the manual says otherwise, because washing collapses the fibre structure that does the filtering.
3. Wash the washable ones on interval, not on symptom.Every one to three months for a bagless machine in normal use, monthly if you vacuum daily or have pets. Cold water only, until it runs clear, squeezed rather than wrung. No detergent — it leaves residue that clogs the media permanently and it can break down the foam.
4. Dry filters completely — a full 24 hours, and longer in a cold house.This is the single most damaging shortcut in vacuum maintenance. A damp foam filter chokes airflow badly, and because that air is what cools the motor, a damp filter overheats the motor. Twenty-four hours somewhere warm and airy, and a hand test that finds no cold or heavy spot in the middle.
5. Replace the exhaust or HEPA filter on time.Typically every six to twelve months, more often with pets or in an allergy household. It is a consumable and it does not recover. A grey, matted or smelling exhaust filter is well overdue, and it is often the reason a machine has started to smell.
6. Replace washable filters too, eventually.Foam perishes — it goes crumbly, loses its spring, tears at the edges or develops a permanent grey stain that will not rinse out. Every one to two years, or immediately if it is torn, because a torn pre-motor filter sends dust straight into the motor.
7. Check the bag or bin filter on a bagged machine as well.Bagged machines still have a pre-motor filter, and because the bag does most of the work people assume it does not exist. Once or twice a year is usually enough, and it is often a card-framed pad that is simply replaced.
8. Log the date on the filter itself.Write the month on the frame in marker as you fit it. Filter intervals are exactly the kind of thing nobody remembers, and a date on the part removes the guesswork entirely.

Tips

• Buying a second pre-motor filter with the machine is the cheapest upgrade you can make. You swap rather than wait a day for drying, so the wash actually happens.
• Rinse from the clean side outwards, so the water pushes the trapped dust back out the way it came instead of driving it deeper into the media.
• Never dry a filter on a radiator, in an oven or with a hairdryer. Heat distorts the frame and shrinks foam, and a distorted filter no longer seals in its housing.
• If your model's filters are hard to find, note the number on the filter frame rather than the machine. Filters are shared across many models and the frame number finds a cheaper equivalent.

Common mistakes

• Washing a pleated HEPA filter — Water mats and collapses the randomly arranged fibres that do the capturing. It will look fine and no longer filter to grade, and it usually never dries properly either.
• Refitting a filter that feels only slightly damp — The middle is always wetter than the surface. It restricts airflow severely, and the motor is cooled by that airflow, so it runs hot and its life is shortened.
• Using washing-up liquid on a foam filter — Detergent residue clogs the fine structure and does not rinse fully out of foam. The filter passes less air afterwards than it did dirty.

If it doesn't work

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