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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 better here is helpful information to explain the impact open windows have on them.

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

Technically speaking the short answer is – yes, but not as well as they should. Before we go any further, let’s consider that the word “works” actually means. Here’s a definition I’ve found to help illustrate it:

2. (of a machine or system) operate or function, especially properly or effectively. “his cell phone doesn’t work unless he goes to a high point” synonyms: function, go, run, operate;

Google definition result

Let’s use a good example. Think about how a refrigerator works. It’s primary task is to cool air inside of it, right? Likewise, an air purifier primarily filters out contaminants from 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 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 in efficiency.

It’s important to understand that air purifiers work by cycling air 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 since the device will have to clean the nearby air all over again. It depends mainly on what you’re cleaning from the air and how much outside air you let in.

Does this mean you should 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 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 air flow the most likely air to get cleaned may be the air closest to it (where it gets pulled in by the fan).

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 thing 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

GermGuardian AC4100 small air purifier on shelf image
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 consider

Diagram of room air flow with windows open air purifer

Air flow 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 air flow is typically much smaller.

If you do decide to open windows, try opening only one in each room. The reason is because 2 or more windows tend to allow more air flow through a room but the drawback is the disturbance in 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.

It simply, in most cases, 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

If you’d like to read more and learn more facts about air purifiers, head over to my informational posts page for lots of great articles that may help.

Let me know you have any questions or feedback!

2 Comments
  1. Thank you for the information. Your article is very helpful.

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