Can You Use an Air Purifier With Windows Open? Read This First!

Should you run an air purifier with the windows open?

This question is very common on the internet today and with a good reason. After all, opening the windows not only lets in more air, but it also enhances natural lighting and cooling.

It also allows the morbid indoor air to escape.

But to answer this question correctly, first, we need to understand how this appliance works.

How air purifier works and why opening windows might help

An air purifier sucks in the contaminated air in the room, purifies it over HEPA filters or other types of filters.

It removes allergens such as dust mites, pollen, dust, smoke, mold spores and in some cases, it even removes viruses.

A fan inside the air purifier then whips the purified air back inside the room.

Now that you have a basic understanding of how this appliance works, well, we can attempt to answer the question:

Can you use an air purifier with the windows open? Yes you can but the air purifier might take longer to purify the air inside your rooms than it would with the windows closed. But if the air from outside is not too contaminated, the air purifier might work just fine with the windows open.

Thus, before you can open the windows to let in more fresh air, you should do some simple math. Ask the following questions:

  1. Is the outside air more contaminated than the indoor air? If yes, keep the windows closed
  2. Is the outside air less polluted than the air inside your home? If yes, open the windows.
  3. Is your purifier large enough to handle the increased air through the purification cycles?

Know when to open and close the windows

The eyes are the entry to your soul and windows and doors are the entries to your home. So, just what does opening the windows mean when using an air purifier?

First, more air will come into the room. Thus, if the appliance would have taken four cycles to cleanse all the air in the room, now, it might take longer than that.

After all, when you open the windows and doors while the purifier unit is still running, it is like restarting the entire process all over again.

So you can open the windows alright, but the most important thing to know is when to close them. Once you feel that you have let in enough air from outside into the room, close the windows.

After all, in a regular room, say, a bedroom, a purifier unit can take a few hours to purify the air. Thus, when you open the windows, it could take many more hours.

Image of running air purifier with windows open

There is no need to run your unit for hours on end since that could shorten its lifespan a great deal.

Thus, open the windows for a short time only. After running your purifier, if you intend to run the appliance for 7 hours, close the windows after 3 or 4 hours. That way, the cleansed air stays inside the room.

Your air purifier filters the same air over and over again

It is impossible to separate filtered and unfiltered air.

Thus, the air-purifying unit filters the same air in the room repeatedly. It is a simple operation.

Let’s assume that your indoor air in a 10 by 12 foot room was 65% polluted with smoke, dust and mold spores.

As you turn on the purifier unit, it pulls in the air, filters it and releases it back into the room. It removes some of the pollutants.

It repeats the process again. Draw in – filter – release. It will do this and every time, the percentage of contaminants reduces!

If you open the doors to all rooms and place your unit facing the doorway, it can help filter the air in all of your rooms.

When you might need to keep the windows closed

Sometimes, you might need to keep the windows closed. For instance:

When the air outside is too polluted

You could run your unit to its death when the air outside is very polluted. In such a case, you are better off keeping the windows closed and keeping all the filtered air inside.

The bad thing with opening the windows is that even the air that your unit filters escapes outside!

Mostly, if you live in a condo, apartment or other urban kind of setting, you are better off keeping the windows closed.

But first, you have to determine the kind of pollutants that you are dealing with. If they are outdoor-originated, such as smog, dust, ragweed, pollen and industrial gases, you should keep your windows closed.

If your air purifier unit is too small

If you have a small urban apartment and an equally small air purifying unit, keep the windows closed.

Otherwise, if you keep it running for too long, you might cause it to overheat. In any case, it will be filtering air at a capacity that it is not designed for.

When you can use an air purifier with windows open

Some instances warrant using your purifier appliance with the windows open. For instance:

When you have many indoor allergens

When your indoor air is contaminated with many indoor allergens such as mold, pet dander, dust mites and musty smell, you might want to allow in more fresh air from outside.

Also, you could be having a lot of book and ultrasonic humidifier dust. In such cases, more fresh air from outside would really help.

Image of should you run an air purifier with the windows open

There is also the heavy matter of VOCs (volatile organic compounds). These gases come from burning fuels. You would be surprised that they are more heavily concentrated in indoor air than outdoor air.

In such cases, open the windows for more fresh air from outdoors.

When you have a large capacity air purifier unit

If you have a large capacity air purifier unit and the outdoor air has less contamination than your indoor air, you can run the unit with the windows open.

A large unit draws in more air than a small unit, doing a faster job! If your home is in the countryside and it is not pollen season yet, open the windows!


So, this far, can you use an air purifier with the windows open? It is hard to give a definite no or yes.

Thus, consider your surroundings keenly and decide whether opening the windows would be more beneficial or harmful.

If you open them, close them at least three hours before you can stop running the air purifier. That way, the air inside the room will be purified without escaping outdoors.

If you need an air purifier for your home, you might consider the LEVOIT HEPA-FILTER Air Purifier from