Do Air Purifiers Work With Windows Open? There’s More To It Than You Might Think!

Air purifiers work by circulating and filtering contaminants like microbes, allergens, pet dander, and many more from the air. At the same time, letting in fresh air is something most of us enjoy doing from time to time. But does it affect how your air purifier works?

You may be asking yourself, “Do air purifiers work with windows open?” To help you understand the facts more easily I’ve put together some helpful information to explain it all.

Answering the basic question – Do air purifiers work with windows open?

Air purifier open window facts

Technically speaking the short answer is –yes, but not as well as they should. Before we go any further, let’s consider what the word “works” actually means.

It’s important to understand that air purifiers work by continually cycling the air in a room and filtering it.

If you open windows, the process is interrupted and your air will be subject to whatever particles are present in the outdoors. Before opening the windows, consider that you’ll potentially be starting over with the air purification process, as the purifier will have to clean the room’s air all over again.

It depends mainly on what you’re cleaning from the air and how much outside air you let in.

Let’s use an example. Think about how a refrigerator works. Its primary task is to cool air inside of it, right? Likewise, an air purifier primarily filters out contaminants from the air around it that cause air quality issues.

If you open a refrigerator, will it still operate? Yes, definitely.

The same goes for an air purifier you’ve got running and cleaning the air in an open room. If you leave its door open, it will still try to cool the air near it as much as possible.

Likewise, an air purifier will draw in as much air is physically possible and filter it.  The performance in a room with windows open is much less than with windows closed.

The problem lies with efficiency.

Should I never open a window with an air purifier running?

No, that’s not the case at all. Basically, you need to think about a few factors before doing so. Ask yourself these questions:

#1. How clean is the air outside near the window you’ll have open?

Is it dirty, polluted, or smoggy? Is anyone burning piles of leaves nearby, for example? It’s a big thumbs down if your outdoor environment is full of smoke, trash, and particles you don’t want indoors!

I’ve lived in ground-level apartments very near the path of passing cars in the past. In some cases having the window open wasn’t a problem. However, some cars with emissions problems or diesel pollution would enter my residence.

#2. Will you remember to close the window later, or do you plan to leave it open for hours? (Will you forget to close it?)

Time is the determining factor for whether or not an open window will or will not reduce the indoor air quality where you live. And your air purifier’s efficiency as well.

The longer the window is left open, the less work that the air purifier can perform. It takes a number of hours to fully clean the air in a standard sized room. Think about how much longer the device will take to do so in the case of having that interrupted.

If a room has air blowing in from outdoors it will still circulate the air and filter it, but because of the disturbance in the airflow the air to get cleaned which is the outside air.

Unfortunately, leaving the window open means the air purifier is not just cleaning the air in the room. It must also clean the air entering the room from the outdoors as well.

As long as that condition is present, you’ll never have fully purified air inside.

Diagram showing air purifiers working with windows open

An air purifier can “work” with the windows open, but it can’t work nearly as well as it would with the room sealed. One significant problem is that contaminants like allergens are re-introduced into the room’s air. It will take much more additional time to complete the purification process. If a window is open, there will always be air containing outside particles.

5 factors to consider before opening a window

Outdoor air pollution facts image with percentages of pollutants
1. Your outdoor environment

I don’t recommend opening windows if you live in a polluted area or one that has car exhaust, smoke, or other pollution issues nearby. Also, definitely don’t leave the windows open during spring because of the high pollen count. That stuff gets everywhere and will consume your air purifier’s filter lifespan more rapidly.

Opening windows means that you’re not just giving the air purifier work additional work to do. You’re also prolonging the time it will take for the air inside your house to be thoroughly cleaned.

For those with allergies, a few seconds of exposure to allergens can be critical. I don’t have allergies but I can feel the effects of pollen & other pollutants in the air. Vehicle exhaust can cause lots of coughing and headaches from time to time. Dust is another issue to contend with, too, and it gets all over the place after a few weeks!

For the sake of your health and quality of living, open the windows only if you live in a relatively clean environment.

2. Your home’s indoor environment

Image of smoke from cooking in kitchen on stove top
Given that you own an air purifier, it’s safe to assume the cleanliness of your indoor air is (now) probably pretty good. Otherwise, something else must have prompted you to open the window.

I totally get it – lots of things can happen. Maybe you burned your cooking and need to let the smoke out FAST! Maybe the garbage has piled up because of a rough week at work & you didn’t have the time. Painting your walls and having to deal with the fumes is another potential reason.

These are honestly all great reasons – you don’t have to have some huge, major cause for opening one or more windows. I love opening windows in the summertime and hearing the kids play outside. It’s one of life’s little pleasures, and I still have fond memories of living nearing a playground many years ago.

An air purifier will keep doing its job, regardless of whether the room is sealed or not.

If you’re like me and live in a fairly nice area with mostly fresh air, the air inside your house should stay clean and filtered as long as an air purifier is at work.

To make the most of your air purifier, keep the time you have windows open to a minimum.

3. The impact on your air purifier

Image of Levoit LV-H132 air purifier in bedroom

Fact: It’s easier for an air purifier to work within confined spaces.

After all, disruptions are minimal. It pulls in air, filters it, and releases it back to the room as fresh, clean air.

The air that it filters is some of the same air it filtered a few minutes ago, and the number of particles that get trapped in each filtration process decreases per attempt.

When you limit the amount of air an air purifier has to clean, you greatly increase its efficiency and the amount of time it will take to freshen an entire room.

However, there’s another issue you might not have thought of: if you’re cleaning additional air from the outdoors, that means you’ll be decreasing the life of the air filter. That’s something to think about.

4. Energy costs

Because of the open window, clean air will exit and unfiltered outside air will enter. When this happens there’s a good chance you’ll be tempted to turn up the fan speed and let the device run for more hours than you normally would.

While it’s not a huge amount of electricity to be consumed (most of today’s small & efficient models like this one one consume 10 watts or less) it can add up over time and is unnecessary.

Less effectiveness = you notice the air isn’t clean = you use your purifier more. That adds up to more money wasted!

5. Time

Image of a digital alarm clock radio showing time 4:00 PM
As I mentioned earlier, the amount of time it takes for an air purifier to fully freshen a room is affected by air space. Take my advice and close the window after a few minutes.

It’s not just whether or not a purifier can work with windows open, but if you are dealing with respiratory problems it can be pretty important. The amount of time you suffer from a lower-quality air environment is directly impacted by how long you will have to keep it running.

In most cases, it only takes a handful of hours for your air quality to greatly improve. Your quality of life can improve accordingly! Severe conditions like cigarette smoke and multiple pets with odors & their dander are some good examples.

How long do you want to prolong having the best, freshest air possible?

Of course, if health problems like asthma and emphysema aren’t an issue, then that’s not really a concern. My goal in bringing this up was to at least give you some food for thought so you can make the best decision for you & your family.

Air circulation factors to know

Diagram of room air flow with windows open air purifer

Airflow with 1 vs 2 or more windows open can be dramatically different. With 2 or more windows open, often the air purifier will have almost no effect. With only 1 window open, there is some external air entering the room but the purifier can at least work with marginal efficiency. This is because the amount of disturbance in the room’s airflow is typically much smaller.

If you do decide to open windows, try opening only one in each room. The reason is that 2 or more windows tend to allow more airflow through a room but the drawback is the disturbance in the air around the purifier. Basically, you defeat the purpose of using a purifier when doing so.

Perhaps you occasionally enjoy listening to the lovely sounds during a warm summer’s night. Wait until your indoor air has been freshened then open only one window. You’ll find it will have minimal impact on the indoor quality where you live in most cases.

Final thoughts and advice to take away

You SHOULD open your windows if:

  • You’ll close them relatively soon or you don’t have immediate health or allergy issues
  • Your outdoor environment is relatively clean
  • Your room is newly painted or fumed
  • There are immediate extreme air quality problems like from a kitchen fire, burns, or garbage, etc.
Note: If you inhale too many Volatile Organic Compounds (VOCs) – a harmful chemical common in paint – be sure to open your windows and not stay in the room for too long. Read more about the symptoms of VOC poisoning here.

You SHOULD NOT open your windows if:

  • You plan to leave them open for extended periods of time
  • Your outdoor environment is heavily polluted
  • You still have air quality issues indoors and the purifier hasn’t completed cleaning it
  • You have significant indoor air quality problems like smoke, pet dander, etc that require additional time to treat

Essentially, there’s no harm in running an air purifier with windows open, but it’s not helpful and you’re better off turning the purifier off while the windows are open.

Simply put, in most cases, it reduces the ability of your air purifier to work as well as it can.

Here are some basic guidelines to remember:

  • Have a heavy source of air problems? (pets, cigarette smoke, etc.) Consider leaving the windows closed
  • Avoid keeping the windows open if you live near a heavily polluted area or during times like spring
  • Ideally, wait until a room has been freshened and the major contaminants have been removed first before doing so
  • Ideally open only ONE window, as it reduces the amount of air from outdoors and the air disturbance created
Grant Williams

About the author

Grant is a professional engineer by trade and has experience with both maintenance and do-it-yourself home projects. He enjoys sharing his expertise & ideas with others to help them improve their comfort and quality of life. Read more »

Your comments are welcome!

  1. What about letting new oxygen into the room? Does the oxygen levels not drop when not letting new air in? Maybe the air that enters when entering the house is enough? (I live in a small two room house)

    • Hi, unless you live in a perfectly airtight home getting in oxygen shouldn’t be a problem. You could always perhaps open a window etc for a little while. If you wanted to enjoy a bit of fresh air but not leave it open a long time while running your purifier.

      An air purifier doesn’t do anything to oxygen in the air – it just moves the air and removes nasty particles.

  2. Hello. I feel like this article doesn’t take into account the Oxygen/CO2 levels in a room, which is very important also. The longer you leave all the windows closed, the amount of CO2 in a room rapidly builds up, to the point where it can have a measurable impact on the people inside the room. Leaving the window closed permanently may mean more ‘pure’ air, but will also undoubtedly create an environment that has poor Oxygen/CO2 levels – leading to lower cognitive performance, for example.

    • Hi Colin. While I can appreciate your comment, it’s not really the topic of this article. Air purifiers don’t affect oxygen levels in a room (aside from ozone generators).

      Oxygen and sleep quality are separate topics and I’m sure worth investigating further but not related to the question at hand. Thanks for dropping by. :)

  3. I would like to know how an open window affects things if the purpose of the air purifier is to help prevent covid if someone in the room may have been exposed. I was told by an epidemiologist that you can use both tools – some air moving from outside and an air purifier. But I don’t know if the ongoing status of that setup like for hours is a problem?

    • Hi Martha. I think a great idea would be to do both but not at the same time. I say that because it will be very hard for the air purifier to clean the air well if the room is open. One idea would be to have two windows open and put a fan in one facing out. That will both pull out the old air to the outside and bring in fresh air.

      (As opposed to only one window and it’s much hard for fresh air to get in anywhere near as quickly). Then run the air purifier with the windows shut. That should do it.

  4. I have cops with bad allergies I am on oxygen. my brother brought me an air purifier it has not helped with allergies and my breathing what do I need to. do to help clean the air in my bedroom ?

    • Hello there, Jean. What type of air purifier is it? A good one that’s the correct size for the room should help with your allergies.

      Best regards.

  5. Can’t you just turn your air purifier off while the windows are open and close windows then turn it on again? Also, our purifier is close to the kitchen and we cook a lot of Chinese food which requires more cooking oil, and gets smoky, is it ok to keep it it on during cooking?

    • Hi Wendy yep you can do that. If the window isn’t a really long time then that would help reduce the amount of outside airborne dust or particulates that are let back in.

      You can keep the air purifier on when cooking, but I would check the filter to see if it’s being clogged up with airborne substances from cooking. If that happens it might be best to keep it off while you’re cooking and be sure to use the exhaust fan if you have one. However, it won’t hurt the purifier.

      Best regards.

  6. I keep the windows closed at night with the air purifier running but should I close the bedroom door? I would prefer to keep it open.

    Excellent article!

    • Hi Angela. Glad you like my article. :)

      It’s ideal to keep it closed, yes (so that it only has to cycle and clean the air in the bedroom, not attempting to do a larger area). However, if the door is closed during the day while it runs that’s probably fine. Hope that helps!

  7. I M mainly interested in decreasing covid in apartmrnt. Should I just ke e p windows closed. What about air confines at same time

    Correction air conditioner

    • Hello Michael. Contagious diseases like that are normally brought in by other people. Fans or air conditioners generally just circulate the air already present.

      In this case I would recommend reading more about ways to deal with it as I don’t want to give you incorrect information. Best regards.

  8. i do lash extensions and work with glue that releases small amounts of formaldehyde into the air, but since i am in close proximity to it, it causes irritation in my lungs and I cough, and so i always keep my room door open (not to outdoor air just indoor) to increase ventilation. with an air purifier i am not sure whether to leave the door open or closed as my goal is just to breathe in air thats not contaminated. since the formaldehyde is continuously being released in the air as i work throughout the day, would it be more effective to let the air purifier do its job with the door closed or keep the door open with the purifier on to keep fresh air flowing in?

    • Hi Chloe any time you’re dealing with something like that it’s always best to keep a room ventilated. In fact, it would be a great idea to use a small fan facing outward from a window to pull out the air and draw in clean, fresh air.

      You could switch off the air purifier if you like until you’re done and the room is closed again. It’s much more important in this case to mainly not inhale something potentially harmful like that (similar to paint fumes, acetone vapors, etc.).

      • Hi. I am very glad I found all this of different viewpoints discussion. Thanks. I live in Athens Greece, center, bad quality of air always.
        In my particular spot/area it’s a bit better, not many cars, few trees. My thing is: There is no way I will close the windows ! Never, not at winter, not at summer, because I can’t stand it. So in this case, I have only 2 windows (not large, and whole flat is 33 square meters) which lead to a balcony, and they are in different rooms.
        I bought an air purifier with HEPA, carbon, and plasma (plasma I won’t use it, I’m scared). My question is….and sorry for all this long description…. WITH OPEN WINDOWS 24/7 , is my purifier at least doing smg? “At least smg” would sound sweet, because now I already bought and payed for it. Or is it all in vain? I am concerned mostly about the ozon pollution of outdoors air, from cars, industries or what. Thanks, I will appreciate if I get an answer !

        • Hi Leonidas. You don’t have to worry about the plasma feature as usually, it’s a tiny amount produced – not enough to be a bother.

          To answer your question: it depends on what’s in the air around it, but it won’t be able to work like it would with the room closed. It will be continuously cleaning the outside air that’s coming in plus some indoors.

          However, note that ozone isn’t something a standard air purifier can help with as ozone is a molecule and not a solid particle like air purifiers remove from the air.

          If you have ozone nearby you can usually smell it (it’s that odd odor you smell after lightning, using electric trains/cars, etc.) so you may not even be subject to it at all. Ozone is usually a problem if you’re around heavy amounts of it. Otherwise it shouldn’t really be an issue. Best regards.


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