How Long Should You Run Your Air Purifier For?

There are several things that make a difference when it comes to how an air purifier cleans your air. How long do you run an air purifier for?

In this article I’ll answer your question and a lot more:

  • How long do you have to run an air purifier before you notice the difference?
  • How long you can run them.
  • Should you keep it on all the time? What about sleeping with one on?
  • Is it safe to leave them on all the time?

Read on to find the answers to these and more.

How long do you need to run an air purifier?

how long do you need to run an air purifier man thinking image

It’s important to understand that air purifiers aren’t needed only when the air quality in your home is bad – they’re also used to maintain good air quality – meaning it’s a little bit more complicated than a simple “how long” answer.

The amount of time you need to run an air purifier depends on several things:

  • How bad the air quality is in the room and the type of problem you’re dealing with (smoke, pet dander, dust, etc).
  • The room size and the airflow rate (cleaning ability) of the air purifier.
Air purifier run time recommendations
  • For first cleaning a room, 1-2 hours is usually enough to cycle and clean the air.
  • I recommend allowing it to run at least 8 hours per day if possible to maintain the air quality.
  • Ideally you’ll have the freshest, cleanest air by running your purifier 24/7. This can be done on the low or medium fan speed settings. (Note: some models have sensors and will adjust fan speed automatically making this a set-and-forget situation)

How long does it take to notice a difference with an air purifier?

To give you a rough estimate, an air purifier that’s properly matched to the room size often needs about 1-2 hours to initially cycle all the air in the room and clean it. Note that it also depends on the fan setting as that makes a BIG difference in how fast the purifier can move the air and filter it.

However, to maintain clean air you’ll want to keep your purifier running many hours per day – even 24/7. I’ll explain more about this as we go.

If your air purifier manufacturer supplies specifications (as many major brands do) you can estimate how long it will take.

How long does it take an air purifier to clean a room?

How long does it take air purifier to clean a room diagram

This diagram helps to show how you can figure out a room’s size in square feet or the total room volume (amount of air) in cubic feet. Once you know this you can figure out how long it takes for a purifier to cycle & clean the air in a room. You’ll need manufacturer specifications to do this (brand name air purifiers normally provide this).

Air purifier manufacturers usually include one or more specifications that tell you both their recommended room size (in square feet) and/or the amount of air they can move in one minute (CFM, or cubic feet per minute). The best air purifier brands include lab-tested Clean Air Delivery Rate (CADR) with their products.

The CADR rating helps you better understand how efficiently a purifier can get rid of air particles. In fact, these purifiers are tested for how well they remove smoke, dust, and pollen particles.

The amount of time it takes an air purifier to clean a room depends on the purifier’s airflow rate (CFM/CADR rating) and the fan setting. Note that the CADR rating is based on the highest setting the purifier has.

This can be from about 20 minutes to 2 hours, depending on the product as well as whether or not you’re using it at a lower fan speed. Using a quieter (lower speed) fan setting will increase the time by at least several times.

Example of how to find the time a purifier takes to clean a room

For example, let’s say you have a room with a size of 10 x 16 x 8 feet (width x length x height). That’s 10 feet x 16 feet x 8 feet = 1,280 cubic feet. We’ll use a popular air purifier called the GermGuardian AC4825 with a smoke CADR rating of 108 for the example.

The time it would take to cycle the room air on the high fan setting would be:

1,280 / 108 = 11.9 (about 12 minutes)

For using other fan settings, some rough estimates would be:

  • Medium speed: (say 1/2 of high) about 2x the time, or close to 30 minutes.
  • Low speed: (let’s say that’s 1/5 of high) about 5 x the time, or about 1 hour.
  • Ultra-low speed/sleep mode: let’s say that’s about 1/20th the fan rate: about 20x the time (nearly 2 hours).

Is it safe to leave an air purifier on all day?

should I leave my air purifier on what I'm not home section image

Yes, in the case of a HEPA air purifier, it’s safe to leave it running while you’re not at home. You can also leave your purifier on all night without having to worry.

I wouldn’t recommend it for an extended period of time (when you’re gone on vacation for example).

Leaving an air purifier running allows it to improve or maintain the cleanliness of the air on a lower fan speed if you like. (As opposed to if it were turned off a long time and would need to run on high for some time to improve the current air particulate buildup).

The idea, basically, is to leave it running for “maintenance” air cleaning.

Note: many manufacturers may recommend running your purifier on high for several hours to initially clean out the worst air particulates and bring the air quality to a healthy level. After that, you can usually allow it to run continuously on a lower (and quieter) setting.

Likewise, you can run your air purifier on low or medium while you’re away to make sure it’s always working. That’s especially true for people with problems like pet allergens or dust – the problem never goes away so it’s best to let the purifier run all the time.

Do air purifiers get hot?

HEPA filter air purifiers do not get hot or have any dangerous parts to worry about when leaving them unattended. Some more advanced models are self-adjusting, meaning that they can sense the air quality and turn on (or run the fan at a higher speed) only when it’s needed.

These types return to a super low-power state or in standby mode. That’s an even more cost-effective way to enjoy clean air.

Air purifiers that aren’t ok to leave on all day or night

Ozone generator example imageAn example of an ozone generator sold as an air purifier. These aren’t recommended and especially for leaving them running all the time as they’ll fill the room with high amounts of ozone. This can cause discomfort and even health problems.

Products that produce ozone (sometimes with misleading and fancy words, but still ionizers or ozone generators in reality) sold as “air purifiers” aren’t good to leave running all day. Ozone acts as an irritant to respiratory passageways and can even cause health issues in addition to discomfort.

Leaving one of these running continuously will cause a large build up of ozone molecules in the air you breathe. They’re not intended to be used for spaces occupied by people but unfortunately a lot of manufacturers don’t tell you that.

Can I run my air purifier 24 7?

Can I run my air purifier 24/7 section image

In the majority of cases, yes, you can run an air purifier 24/7 to keep your indoor air healthy & fresh. That’s because of how air purifiers work. There are a few side notes, however, that I’ll share with you.

NOTE: to be clear, in this article when I refer to “air purifiers” I’m referring to the most common (and safe & effective) type. These are air purifiers with a High-Efficiency Particulate Air (HEPA) filter, not ozone generators or ionizers sold as “air purifiers.”

Why you can run your air purifier for long periods of time

Air purifiers work by continuously cycling filtering the air in a room, trapping airborne particles in their HEPA filter. That means in order to get clean, fresh air in your home you can leave an air purifier running to do its job.

However, there are some things to know:

  • Not everyone has the same clean air obstacle. For example, smokers have a much harder air quality problem to deal with which will take more time & an air purifier that performs well.
  • When you first begin using an air purifier or an air quality problem happens again, you’ll need to give the purifier time to run on a higher setting (medium or high) to get the air back down to a fresher & more comfortable cleanliness level. Once that’s done it’s fine to leave it on a lower setting unless you need to change it.
  • Under normal conditions, it’s often fine to leave a purifier continuously running on a lower fan speed mode once you are able to improve the air. The air in your home should stay fresh & clean.
  • Windows should be kept closed while in use.

Do air purifiers use a lot of electricity?

Winix HR900 air purifier power measurements in Watts diagram

Some common air purifier electrical power draw measurements made with a Kill A Watt power meter for a Winix HR900 model large room purifier. This is similar to the power use of other purifiers as well.

The power draw of a purifier depends on several things, but here are some pretty common average power use numbers I’ve measured:

  • Standby/off: 0 to about 1W.
  • Ultra-quiet/sleep mode: around 5 watts.
  • Low speed: about 8 to 15 watts
  • Medium: about 15W – 25W
  • High or turbo mode: about 45 to 55W.

The great news is that most purifiers use only a little power for the most common settings (low and medium). Even very large room purifiers with a really powerful fan still use a very moderate amount – about the same as a ceiling fan.

How much does it cost to run an air purifier?

how much does it cost to run an air purifier section image

It’s not too hard to figure out how much energy air purifiers use per day, week, month, and even in a year. Once we do that we can estimate how much it costs to run one for each period of time.

To do that we need to come up with some simple estimated numbers and also we need to know about how much our electrical power company charges. Power companies bill the power you use with a rate called cents per KiloWatt-hour. A kilowatt-hour is just the amount of power used by appliances multiplied by the amount of time they’re running.

This makes it simple to figure out how much it costs to run an appliance.

Figuring out air purifier energy use costs

Let’s take an example based on the way most people would use air purifiers. Let’s use the following numbers:

  • Fan speed & power use (estimates): 9 hours on low (overnight) at 15W, and 15 hours (during the day) on medium at 25W, for a total of 24 hours.
  • Georgia, USA average electricity cost: $0.1101 per Kilowatt-hour (kWh).

Based on this, here’s a convenient table showing how much it costs to run an air purifier.

Air purifier use cost table

Time Cost
24 hours $0.05616
1 week $0.39
1 month $1.74
1 year (365 days) $20.50

As you can see it costs very little to use yours 24 hours a day. That of course would go up a little bit if it’s left running on the highest speed but not a huge difference. As you can see, keeping you air clean & healthy is very affordable!

Should I sleep with my air purifier on?

air purifier running at night man sleeping graphic image

Indeed, if you like you can sleep with an air purifier on with no problems. Air purifiers don’t cause problems as they simply remove particles from the air – they don’t add anything to it.

Additionally, leaving them on all night is a good way to be sure the air is kept clean all the time. However, if you’re a light sleeper like me you may want to consider a model with a “sleep” mode feature.

As some air purifiers can be somewhat noisy, a sleep mode is an ultra-quiet mode that keeps the purifier running but with a very low speed that’s nearly impossible to hear. Some models also dim the control panel lighting as well.

Grant Williams

About the author

Grant is a professional engineer by trade and has experience with both maintenance and do-it-yourself home projects. He enjoys sharing his expertise & ideas with others to help them improve their comfort and quality of life. Read more »

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