HEPA, Carbon and Ion-Exchange Replacement Filters

HEPA 13, True HEPA and combo filters: reading the grade

Filter grades follow two standards. True HEPA refers to media that captures at least 99.97 percent of 0.3 micron particles, while HEPA 13, or H13, comes from the European scale and means at least 99.95 percent at the hardest-to-catch size. Both suit allergens, dust and smoke particles. A combo filter stacks HEPA with activated carbon so one cartridge handles particles and odors, and quoted hours of life are the maker's estimate rather than a guarantee.

Fit matters as much as grade. Filters are made for particular units, so match the maker's code and the listed dimensions. Some pre-filters come as a large sheet to be cut down to size, which only works if you trim to the unit's opening. Many multi-packs hold copies of the same filter, so check whether a two-pack covers two changes or two different stages.

Wick and ion-exchange filters: protecting a humidifier from minerals

Humidifier filters deal with water rather than air. A wick filter absorbs water so a fan can evaporate it, and traps minerals as it does; it stiffens and discolors with use and should be replaced rather than cleaned indefinitely. An ion-exchange cartridge lowers the dissolved mineral content before the water becomes mist, which cuts white dust and scale. Both are specific to the humidifier model, so check the code on the unit or in its manual.

Questions about HEPA, Carbon and Ion-Exchange Replacement Filters

Are non-original filters as good as the maker's own?

Only if they match the unit's code and dimensions. Generic filters may fit but can use thinner media or seals that leak around the frame. If you try one, check for a tight fit with no visible gaps and a listed grade such as True HEPA or H13.

What does the activated carbon layer do, and does it wear out?

Carbon adsorbs odors and some gases such as cooking smells, but it fills up and then stops working, with no obvious sign. It often needs replacing sooner than the HEPA layer, so follow the interval or replace it when odors come back.

What does a pre-filter do?

A pre-filter is a coarse layer in front of the main filter that catches hair, lint and large dust. It keeps the HEPA or carbon layer from clogging early, so the main filter lasts longer. Many pre-filters can be vacuumed or washed if the maker says so.