When to Change A HEPA Filter Air Purifier

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Updated January 12, 2023

HEPA Filter Air Purifiers are medical industry-approved top-performing air purifiers that outperform many other kinds of air purifiers on the market, but many people don’t realize that knowing when to change a HEPA filter is key to making sure your air purifier is functioning at optimal levels at all times.


  • Increased allergies indoors are a good sign that an air filter needs to be replaced
  • HEPA filters are capable of filtering out pollutants 300 times smaller than a strand of human hair
  • Regularly changing your air filters can save you anywhere from 5-15% on your energy bill

Below we’ll discuss all the signs that it’s time to change your filter and why it’s important.

Common Types of Air Purifiers

  • HEPA- an acronym for High-Efficiency Particulate Arrestance filters which have become the high-performance option because they’re rated to capture 99.97% of impurities (particulates) as small as 0.3 microns in diameter, which is 300 times smaller than the average strand of human hair.
  • Ultraviolet Air Purifiers- Residential UV air purifiers are small and compact purifiers that use ultraviolet light to remove bacteria, viruses, and pathogens from the air by breaking molecular bonds in the DNA of such pollutants.
  • Activated carbon- Activated carbon air purifiers a good at handling smoke, odors, fumes, and gases, and additionally tend to include HEPA filters that remove particles as well, making them versatile
  • Ionic Air Purifier- an ionic air purifier emits negative ions, which bond with airborne particles such as dust and dander which are positively charged. This makes the particles heavy enough that they fall out of the air. These are quiet and motor-free air purifiers that are gaining popularity amongst consumers.
  • Electronic Air Cleaner- An electronic air cleaner works with a home’s furnace or air conditioner using both a HEPA filter and positively charged ions to trap particles and clean the air. They’re pricier than some options but are a good solution to air purification for an entire residence instead of just a room.

If you are not keen on what size air purifier you need, you may often change HEPA filters. When the room is too large, the air purifier may end up overworking, which might make your air purifier smell. This is because air purifiers have a specific range that can filter air effectively.

Air purifiers are highly effective for emphysema, especially in conjunction with other purification types. The high sensitivity of HEPA filters means they have to be changed more often than other filters. This is why it’s so important to understand when your HEPA filter needs to be changed. It also matters where you put your air purifier and get the right one, especially if you’re considering plant air purifiers.

Signs Your HEPA Filter Needs Changing

According to the International Association of Certified Home Inspectors, there are multiple signs that your high-performance HEPA filters likely need changing.

Pet Dander

If you’re suddenly having allergies acting up more than usual and finding pet dander in places you normally don’t, there’s a good chance you need to change your filters and start doing so at least once a month. Pet dander can become airborne and start to circulate in a home or building’s ventilation system, which of course, can cause allergies to flare and pet dander to be spread in places it normally wouldn’t be.

Insider Tip

If you’re suddenly having allergies acting up more than usual and finding pet dander in places you normally don’t, there’s a good chance you need to change your filters and start doing so at least once a month.

Increased Allergies or Breathing Issues

Even without pet dander in the air, a filter in need of replacing can become far less effective, and thus allergens and other irritants often filtered out become airborne or simply increased in air density. If you suddenly notice allergy flare-ups that are more extreme or frequent than normal, or if you’re having any other breathing issues, it’s a good idea to check your filter.

Sudden Increase or Spikes in Power Utility Bill

A sudden increase in your electricity bill can indicate your filters need changing. Air filters have an enormous effect on general home energy efficiency- if your power bill suddenly goes up, a dirty filter may be the culprit, in whole or part.

Insider Tip

A sudden increase in your electricity bill can indicate your filters need changing.

Testing Filters

Though all of the above are good indicators of a filter needing replacing, there are two easy ways to confirm this if you’re still unsure.

White Sheet Test

When applicable, hang a white sheet a few inches away from the purifier, or vent in your home or building and leave it for an hour. If, after an hour, the sheet has turned gray or black, you’ve definitely got a filter in need of replacement- the dirtier the sheet, the less effective the filter has become.

Remember that you should hand-wash your Electrostatic filter once a month using a garden hose and a power spray nozzle. Ensure it is dry before inserting it back into your air purifier.

Eye Test

If you’re too busy or otherwise can’t perform the white sheet test, you can still visually inspect the filter for dust and dirt to see if it’s bent, contorted, or damp.


Why should I change my air purifier filters on a regular basis?

A filter that’s dirty, clogged, or filled with pollutants from overuse will become far less effective at filtering pollutants, allergens, and irritants from the air, diminishing the air quality in your home, and it will also make it more difficult for air to pass through, meaning your purifier and ventilation system has to work harder increasing energy costs.

How often should I change my air filters?

The answer to this can vary considerably depending on the size of the ventilation system and the building it services, as well as ambient air quality in the building, and the hours per day your purifier is running. However, most professional home inspectors recommend you should be changing your filters a minimum of once a month.

Do all air filters need to be replaced regularly?

Some kinds of air filters are designed to be washable, which reduces the frequency that they need to be replaced, however, HEPA filters, which are considered the most effective on the market, are not washable and do require periodic replacement.

What do air filters do?

The basic function of any air filter in a ventilation system is to clean the air that is circulated through the building by stopping pollutants, contaminants, and allergens such as pollen, mold spores, dander, and dust and keeping them from affecting the air quality of the home or facility.

STAT: HEPA stands for High Efficiency Particulate Air filter (source)

STAT: HEPA filters are capable of filtering out up to 99.97% of microparticles The Department Of Energy reports that running your ventilation system with clogged air filters can increase your energy consumption by 5-15% (source)

STAT: HEPA filters are capable of trapping particulates that are as small as 0.3 microns in diameter- or 300 times smaller than a strand of human hair (source)

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