The filter is the part of an air purifier that does the work, and it wears out. A clogged filter moves less air, makes more noise and can smell musty. In humid Singapore, it pays to keep an eye on it.
This guide covers how often to replace each layer, the signs that it is time and how to avoid buying the wrong replacement.
How often to replace each layer
Pre-filters are usually washable and need cleaning every two to four weeks. HEPA filters typically last 6 to 12 months. Activated carbon layers also last about 6 to 12 months, or less if you have strong odours.
These are general figures. Check the manual for your model, because filter life depends on the size of the filter and the CADR of the unit.
Signs that a filter is spent
Weaker airflow, a louder fan, a visibly dark or clogged filter and a musty smell when the unit starts are all signs. Many purifiers have a filter indicator light that counts running hours, which you reset after changing the filter.
Do not rely on the indicator alone. In haze season or with pets, the filter can fill much faster than the hours suggest.
What you can wash and what you cannot
Wash only what the maker says is washable. A foam or mesh pre-filter can usually be rinsed and dried completely. A HEPA layer cannot, because water damages the fibres. A wet filter put back into a unit also encourages mould.
Choosing a compatible replacement
Match the model number first, then the dimensions, then the grade. A filter that is slightly too small leaks air around the edge. Look for a stated H13 or H12 grade, a carbon layer if the original had one and a gasket that seals.
Be careful with listings that say 'HEPA type', and read the latest reviews for comments on fit.
Work out the running cost
Divide the price of a set of filters by the months it should last, and add delivery. A purifier with a cheap unit price and expensive filters can cost more over two years than a pricier unit with cheap filters.
Keep a spare set before haze season. Orders from overseas take days, and popular filters sell out.
Frequently asked questions
How do I know when to change my air purifier filter?
Weaker airflow, more noise, a dark filter or a musty smell. Many units also have an indicator light that you reset after replacing the filter.
Are compatible filters safe to use?
Many are fine if they fit well and state a real filter grade. Avoid filters that do not seal and check recent reviews for fit and smell.
Can I vacuum a HEPA filter?
A gentle vacuum of the surface can remove loose dust from some filters, but the maker's guidance comes first. Do not wash it.
