You may be tempted to try and clean and reuse your HEPA filter, even if the brand says to discard it after use. But keep in mind that it won't work with the same rigor afterwards. There are several different methods you can use to clean the HEPA filter, but it's important to know if it's a permanent or washable filter before attempting to clean it. Most permanent HEPA filters can be gently cleaned with a vacuum, while a washable HEPA filter can be cleaned by rinsing it with cold water.
Note that there are no officially defined standards or terms as to what type is considered permanent or washable. If you're not sure if the HEPA filter can be cleaned, look for the “washable” or “permanent” label on the packaging box or on the air cleaner's website. Washing anything, over time, will wear out what is done, and HEPA filters are no different - just that they will suffer damage faster. If the filter is marketed as washable or permanent, you may be able to wash or clean it and it will continue to work.
However, there is no standard for washable HEPA filters, and there have been no public studies to prove how well these filters work after being washed. The manufacturer may have found a method to make filter fibers that won't be damaged by cleaning, but there's really no way to know for sure, so you take a risk. There's a reason most air purifiers suggest replacing HEPA filters after a certain amount of time, and many even come with indicators to let you know when that time has come. Once the integrity of the filter is compromised, it will no longer trap harmful particles in the air.
Air ionizers and ozone generators don't use filters, so there's nothing to clean and reuse. You should be careful not to touch the filter material, only allowing it to come into contact with water. You can tell if the HEPA filter is dirty when an air purifier struggles to capture air pollutants in the air. This is because it is impossible to extract all the particles trapped in the filter using a vacuum, since the filters are made of very strong fibers. There is also the possibility that, given all the particulate matter (dust) that accumulates in a HEPA filter, it can provide the right conditions for mold growth.
Cleaning the HEPA filter is one of the most important things you can do to make sure your air purifier is in good condition. The results show that suction made little or no difference to the performance of their HEPA filters. In practice, HEPA filters are made of a variety of materials, including “thick glass fibers, coated animal hair, vegetable fibers, synthetic fibers (such as polyester or nylon), synthetic foams, metallic wool or metals, and expanded sheets” according to the EPA. Most air purifier manufacturers will tell you how long their filters last in the box, in the manual, or on their website. If you must clean your HEPA filter, be sure to use one marketed as washable or permanent and use the correct cleaning method for the type you purchase. While a HEPA filter claims to remove particles from the air and improve indoor air quality, they can be costly - especially considering ongoing replacement costs.
Once a filter has reached maximum capacity for harmful particles, it will need to be replaced with a new one.