How Long Does an Air Purifier Take to Clean a Room?

People buy air purifiers for a variety of reasons. Some of us can’t ever seem to efficiently deal with cigarette smoke, while others are trying to alleviate asthma and allergy symptoms. Air purifiers are meant to deal with many things regarding air quality, but how long should you actually run one for maximum effect?

The answer to this question depends on multiple factors that we will get into in this article. The key ones among them are:

  • Room size
  • Speed setting of the air purifier
  • Purification method

Room Size

First things first. In order to determine how long you should run the air purifier, you first need to assess the size of the room. It’s really important to have an air purifier with a cleaning capacity that’s suited for the space. Almost all of the products have an approximate room size they’re suited for, but another measuring stick is the CADR.

CADR, or Clean Air Delivery Rate, is an independently developed air purifier rating by AHAM. We talked about that magical number at length in our article for air purifiers for cigarette smoke, where you can also find a list of our suggestions, should you be interested in buying a new device.

So, if you have a bigger room, but your air purifier has a lower CADR rating than needed, you might need to run it for a longer period of time. On the other hand, if the unit has a high CADR but it’s in a smaller room, it will take less time to clean the air.

The Speed Setting

This is an easy one. It’s only logical that if you run the air purifier at a high-speed setting, it will do its job faster. Contrarily, if it’s at a lower speed setting, it will take more time to fully cycle out the air. Some of the more modern air purifiers have an automatic setting and will adjust speeds according to the amount of pollutants in the air.

Purification Method

It’s one thing for an air purifier to have powerful fans and to be able to move the air in the room, but doing so while keeping the air clean is entirely different. This depends on the quality of the filter and how efficiently it eliminates small harmful particles. If the filter is of lesser quality, it would need more cycles to purify the air, thus it would have to run longer.


So, to sum it all up, if you have a room air purifier with a high-quality filter, an adequate CADR and run it at a high speed, you can expect it to clean the air in one to three hours and you should notice a difference in the first 20 minutes.

But, no living space is a closed system and new harmful particles are constantly introduced in the air. Having said that, it would be optimal to keep the air purifier on at all times, even if that means that it runs at a lower setting.