# Air Changes Per Hour Explained

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Updated January 13, 2023

If you are looking at different best air purifiers before making a purchase, you may be wondering how many times should an air purifier change the air per hour. We have got your answers.

KEY TAKEAWAYS:

• Generally speaking, the more times an air purifier can change the air per hour the better.
• This metric is measured via air exchanges per hour, otherwise known as ACH.
• When companies advertise a particular ACH, it is usually in a small room with the purifier running at its highest setting.

## How Air Purifiers Tend to Work

Most modern air purifiers work by pulling in air from their immediate surroundings. This air is then filtered or ionized before being released back into the atmosphere. Keep in mind, that it will take a few days to notice a difference when using an air purifier.

Insider Tip

A good CFM to shoot for is 400, which will translate to a 4 ACH in a large room of 1,500 square feet.

### How do Air Purifiers Calculate the Changes of Air Per Hour?

When referring to how many times air purifiers change the air per hour, it is important to know the correct terminology. This metric is measured via something called air exchanges per hour, otherwise known as ACH. This measurement is calculated by taking the cubic feet of air that can be cleaned in a minute (CFM) and multiplying it by 60 for an hour.

### How Many Times Should an Air Purifier Change the Air Per Hour?

There is no hard and fast rule here, as it will depend on the size of your living space and your individual needs. Most modern air purifiers will list either the ACH number or the CFM number in the instruction manual or advertising material. A good CFM to shoot for is 400, which will translate to a 4 ACH in a large room of 1,500 square feet. This means that the air will be changed in the room four times per hour. This number will naturally increase if you place the purifier in a smaller room.

It is important to note that when companies advertise a CFM or ACH number, it has very likely been measured when the purifier was running at its highest setting. Keep that in mind as you shop.

Insider Tip

An average ink cartridge will be able to print anywhere from 120 to 220 pages before needing to be replaced.

### Benefits of Changing the Air Multiple Times Per Hour

There are some fantastic benefits to choosing an air purifier that can cycle a room’s air multiple times in one hour.

#### Reduced Odors

A purifier with a good ACH rating will be more efficient when it comes to eliminating foul odors in the fastest manner possible.

#### Decreased Airborne Pollutants

The more your air gets changed, the less airborne pollutants will be allowed to float around. Running your purifier at its highest setting will make sure these pollutants and pathogens are taken care of. Keep in mind, that you will want to be sure you’re changing the ozone plates on your air purifier regularly as well.

That said, some more maintenance tips include how often you should change the air filter, how long should you keep an air purifier running, and how to get a bad odor out of an air purifier.

Warning

It is important to note that when companies advertise a CFM or ACH number, it has very likely been measured when the purifier was running at its highest setting.

### F.A.Q.

How many air changes per hour do you need?

This will depend on what your circumstances are. Some homes do not accumulate too much dust, in which case you could get by with one or two changes per hour. Other homes may require three or more.

What are air changes per hour?

Air changes per hour, otherwise known as air exchanges per hour (ACH), refer to the number of times the air in a room is completely recycled in a given hour.

Should I run my air purifier all of the time?

Running your air purifier all of the time is a good idea for some types, such as HEPA purifiers, as this will increase the number of air changes per hour.

STAT: Choosing a HEPA filter with a rating of 99.97% at .3 microns or better will ensure the capture of extremely small particles like viruses and bacteria. (source)