How Long Should You Run A HEPA Filter?

Air purifiers have become a necessity these days because of their benefit of removing harmful particles in the air. But is there an optimal way of using it to maximize its benefits? How long should you keep it running during the day? That's what we asked the experts, and here's their answer.

Experts advise that you run your air purifiers with HEPA filters for 12 hours or more to maintain the cleanliness of your indoor air. You can also consider your air purifier's ACH and CADR to see how its performance can satisfy your need to remove pollutants in the air inside your home.

Keep on reading to know more about how long you should run a HEPA filter to optimize its performance and get the most out of it. This article will also answer if you can run your air purifier 24/7, if you should close your windows when using an air purifier, where is the best place to put it in your room, and if these HEPA filters are toxic. Let's begin!

Hands changing air, dust, carbon and hepa purifier filters. How Long Should You Run A HEPA Filter

How long should I run my air purifier?

HEPA filters or High-Efficiency Particulate Arrestance or High-Efficiency Particulate Absorbing filters have become the standard for the efficiency and effectiveness of filters used in air purifiers. These filters are said to be effective in removing 99.97% of the pollutants in the air. This includes pollen, pet dander, bacteria, dust, mold, and other particles that are at least 0.3 microns in size.

If it is your first time hearing about this unit of measurement, just think of it this way. A strand of your hair has a diameter of about 50 to 100 microns. Now, you have an idea of how small these contaminants are that we're talking about.

HEPA filters can do this because they are made of hundreds of thousands of fiberglass fibers that have been interwoven to form a fine mesh. They can trap even the microscopic pollutants in their mesh so that they would no longer contaminate your indoor air quality.

So, essentially, when we're asking how long we should run our HEPA filters, we're referring to air purifiers using these filters. These are devices that help improve the quality of indoor air.

Experts recommend that you use your air purifiers with HEPA filters at least 12 hours a day to maintain good air quality indoors. However, for those who are concerned about their energy consumption and the HEPA filters being overused, you can check these factors to guide you in your decision on how long to run your HEPA filters.

woman sleep with Air purifier in cozy white bed room for filter and cleaning removing dust PM2.5 HEPA in home


This means Air Changes per Hour. This refers to the speed of your air purifier or how fast it'll be able to clean the air around it.

Check the product information on your air purifier to know its ACH performance. If it says 1 ACH, it means it needs one hour to clean the indoor air.


This stands for Clean Air Delivery Rate. It pertains to how many contaminants the air purifier can clean at a given time. Again, you need to refer to the product information to know its expected performance in reference to room size.

EPA requires air filters to have at least 65 CADR for a room with a size of 100 square feet. Make your adjustments regarding the CADR of your unit and your room size.

Consider your air purifier with HEPA filter's ACH and CADR to determine its optimal running time in your home. Just think of all the health benefits that you stand to gain from this! 

If you or your family members are prone to allergies and asthma attacks, you will be relieved that these filters are doing the work for you to experience fewer symptoms or attacks. Air purifiers also help get rid of the irritating smell of tobacco smoke. Your home is cleaner and healthier.

Dust HEPA Air Filter Cartridge

Is it OK to run air purifiers all the time?

Air purifiers can filter your indoor air within 45 minutes to 3 hours, depending on their individual performance. But considering the benefits that users stand to gain from breathing in cleaner and healthier air, it is understandable why some people would want to have their air purifiers running all the time. This is especially true for those with allergies, asthma, and experiencing respiratory issues.

Experts see no problem with using air purifiers 24/7. This will help you ensure that the highest quality of indoor air is maintained. When you turn the unit off, it will stop filtering the contaminants present in the air. The thing is since air is constantly flowing, new pollutants are introduced most of the time, especially when you open the door or windows.

By having your air purifier running all the time, the contaminants are caught immediately, so they don't float around and affect your health negatively.

Some air purifiers also have a monitoring system wherein they automatically go on standby mode once they detect that the air quality is within the desired level. They will only work again when their sensors recognize that pollutants are present in the air again.

This also addresses concerns regarding overheating and overusing the HEPA filters. They won't have to work as much anymore when there are fewer air contaminants in the room.

In turn, you can sleep and breathe better inside your house. This is especially beneficial for those who stay inside their homes most of the time.

Should you close windows with an air purifier?

When the windows are open, you allow outside air to flow into your house. While this is good for ventilation, take note that along with this comes the pollutants that are present in the air outside such as pollen, dust, and vehicle smoke. It makes sense therefore to close your windows and doors if you want to control the level of contaminants in your indoor air.

However, air purifiers would still work even if you leave your windows open. It is basically their job to trap the pollutants in the air wherever they are coming from. Studies show that air purifiers are still able to reduce the level of contaminants in the air by 60% even when the windows are open.

Of course, they would have to work harder than if you keep the windows closed. More contaminants will be introduced each time that outside air flows inside. But be assured that these devices will help you achieve cleaner and healthier air at any given circumstance.

woman changing the dirty air purifier filter after using for a long time in the dirty air environment

Where is the best place to put an air purifier?

You have to put your air purifier in a strategic location so that you can get the most out of it. You have to consider your breathing zone and the airflow in the room.

Breathing zone

Of course, you put the air purifier in a place where you're staying or at least spending most of your time. It should also be near your breathing zone. The closer it is to you, the better. This means that the purified air needs to travel only a short distance before it gets to you, so you inhale uncontaminated and healthier air.


There are vertical and horizontal air movements inside the room. It is recommended that you place your air purifier at least three feet off the ground to capture contaminants from all sides. Take note also that there shouldn't be any obstruction in front of it so that it can take in as much air as possible and have it purified.

Put the air purifier above the ground and near you so that you can maximize its benefits.

Are HEPA filters toxic?

There have been some issues raised regarding the safety of using HEPA filters. This is due to their shedding of fiberglass fibers, especially when they're new.

If you recall, HEPA filters are made of microscopic fiberglass fibers. These are eventually released into the air as you use them. Therein starts the concern regarding the possibility of inhaling these fibers and what they can do to your respiratory system. Some are worried that prolonged exposure could lead to lung cancer.

Studies have shown that HEPA filters do shed their microfibers, and they get mixed up with the other particles in your indoor air. But they're not considered nuisance dust. They're just like normal particles found in your indoor air. In other words, these microscopic fibers aren't harmful. So, these HEPA filters aren't toxic.

HEPA filters also reduce shedding the longer you use them, so you won't be exposed to their microscopic fibers for too long.

PM 2.5 concept. Used dust filter HEPA. How Long Should You Run A HEPA Filter

Final Thoughts

You can run your air purifiers with HEPA filters for as long as you like. You can keep it running 24/7 or just turn it on for 12 hours to conserve energy. It would depend on your need to have your indoor air cleaned from pollutants so you can enjoy fresher and healthier air inside your home.

To read more about related topics, feel free to visit the following posts:

Does a Dyson Air Purifier Remove Pet Hair?

How Many Air Filters Does A House Have? [And Where Are Filters Located]



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