Should I leave my air purifier on when I’m not home?

There is no need to leave your air purifier running when you are not at home. A good air purifier with the right CADR and ACH can clean the air in a room within 15 minutes. Leaving your purifier running reduces the lifetime of the filters and needlessly increases your electricity bill.

To assess if an air purifier should run while you are not at home we need to take a look at the following:

  • What an air purifier actually does
  • What happens when you leave it on
  • What happens when you turn it off, and;
  • How quickly it can clean your room when you get back


An air purifier constantly fights incoming poor air

An air purifier uses several filters to remove particles from the air. In this way, it creates better air quality since many airborne particles are related to negative health effects when inhaled.

Since every room has (and should!) have good ventilation that is constantly working to provide fresh air, an air purifier is constantly cleaning this incoming air.

Just to be clear, ventilation is the most important thing you can do to improve your air quality. An air purifier can help when your outdoor air is particularly bad, or if you do not want much ventilation due to cold outdoor air. However, you should not both open windows for ventilation and run the air purifier at the same time.

You will always have some ventilation by natural airflow through cracks and openings in walls doors and windows. Your air purifier is an excellent tool to make sure your air is fresh when you can’t fully ventilate.


What happens when you leave on your air purifier while not at home

if you leave the air purifier on, the air in the room will be relatively clean compared to fresh air coming in from ventilation. Therefore, cleaning the air results in a difference in air particles between the cleaned room and the areas around it such as adjacent rooms or the outdoors.

This works similarly to for example two connected tanks full of water. If you are removing water from one tank, the water will flow to be evenly spread across both tanks. So, if you leave the air purifier on, relatively poor air is constantly flowing into the room.

If you leave the purifier on while not being at home, it will constantly filter out the incoming fresh air. This will clog the filters, resulting in having to replace them sooner.

leaving the air purifier running will result in a constant airflow toward your room. The filters will work to keep the air clean, resulting in an accumulation of particles, reducing the lifetime of the filter.

However, leaving the air purifier on will make sure the air stays clean. In this way, when you get home, the air is still very fresh and clean.


Reasons to not run the air purifier

I suggest turning off the air purifier for the following reasons:

  • Running electrical appliances without anyone at home comes with some safety risks
  • Running an air purifier constantly increases your electricity bill
  • The filters will need to be replaced sooner
  • It takes little time to clean the air after you get back


What happens when you turn off your air purifier while not at home

When you turn off your air purifier, air exchange between different rooms and the outside air results in a return of particles that were filtered out by the purifier. However, these particles will not continuously build up. The air in your room will simply reach the same composition as the air that is coming in due to ventilation.

How quickly the air becomes ‘dirty’ again entirely depends on the amount of air exchange. This depends on many factors such as your HVAC system and the opening of internal doors.

Since a proper air purifier takes around 15 minutes to clean the air in the room, you might as well have it clean the air when you get back. This saves your filters and your electricity costs.

Of course, this assumes that you have a proper air purifier that cleans the air quickly and that you do not mind waiting 15 minutes for your air to be perfectly clean again.



How quickly does an air purifier clean the air in the room?

How fast an air purifier can clean all the air in a room depends on several factors. These include:

  • Size of the room
  • CADR (Clean Air Delivery Rate) rating of the air purifier
  • ACH (Air Changes per Hour) of the air purifier
  • Condition of the filters
  • How healvily the air is polluted

For a standard-sized living room of 300 square feet (28 m2), an air purifier with the correct CADR (clean air delivery rate) and the correct ACH (air changes per hour) takes about 15 minutes to fully clean the air.

If you want to know more about how long you should run your air purifier and what CADR and ACH are exactly, you can read my article: How long should you run your air purifier?


Eco mode is a good alternative to keeping it running

Some air purifiers come with an eco mode. An eco mode is a mode for the air purifier that tries to save energy without compromising on your air quality. this feature relies on detecting air pollution and only turning on when levels are above a certain threshold for which purification is needed. When air pollution levels are low, the device turns off to preserve energy.

Since not every air purifier has a detector for air pollution, most air purifiers do not have an eco mode.


An excellent and affordable air purifier is the Coway Airmega. It has the best particles filter (HEPA) as well an odor filter and an eco mode. You can find it on amazon.com.


Should you run your air purifier 24/7?

Constantly running your air purifier ensures that the air remains as clean as possible. However, you do not need to run your air purifier all the time. A good air purifier only takes 15 minutes to clean all the air in the room. Therefore, you can turn it off when you leave and save your filters and electricity costs. If your air purifier has an eco mode, you can switch to that after 15 minutes of run time.