How Many Air Purifiers Do I Need? (Explained for All Rooms)

Josh Mitchell

Written By

Josh Mitchell

Expert Reviewed By

Holly Curell

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Key Takeaways

  • The number of air purifiers you need depends upon the size of the room as well as the air purification capacity of the device.
  • Smaller rooms may require a single air purifiers where as a larger room may require multiple air purifiers placed in different locations.
  • If you want to purify your entire home, you will need to install whole-house air purifiers connected to your existing HVAC system, or separate portable air purifiers in each room. 

Over the years, I’ve come across people with one tiny air purifier for their entire 4,000 sq. ft. house, and I’ve helped people with multiple purifiers in their small garage. Both scenarios are far from perfect.

Air purifiers are an effective way to improve indoor air quality as long as they are used properly. 

Part of getting the most out of your purifiers is knowing how many you need.

So how many air purifiers do you need, especially if you need to purify more than one room?

I’ll walk you through it in the guide below.

Average Air Purifier Capacity Explained

The first thing I tell people who don’t have an adequate number of air purifiers is that air purifiers have ratings that correspond to the volume of air they can effectively purify.

The average air purifier airflow is 200 cubic feet per minute (CFM), meaning it can clean that much air in a minute.

To calculate the unit’s hourly cleaning capacity, we need to multiply this number by 60, resulting in a 12,000 cubic feet per hour cleaning capacity.

While one purifier can effectively clean 12,000 cubic feet per hour, you’ll need multiple air purifiers for an entire 1,000 sq ft home that requires cleaning of 32,000 cubic feet of air per hour.

So always consider the room size and the number of air purifiers necessary to achieve optimal indoor air quality.

How Many Air Purifiers Do I Need For My House?

How many air purifiers do i need

To determine how many air purifiers you need, you need to know how to calculate if you need additional air purifiers. 

The two main factors that will determine if you need multiple air purifiers in your home are

  • Square footage of the covered area
  • The airflow or capacity of the air purifier.

Keep in mind, you might not necessarily need a second air purifier or an air purifier for every room, but you can move one around to circulate the high-traffic areas.

Also, buying multiple cheap air purifiers isn’t the solution, either. One air purifier with better air cleaning efficiency will work better.

Let’s start by calculating the volume of air in a room or home. You need to use the following equation.

Volume (Indoor Air) = Indoor area (sq ft) X Ceiling Height in feet

Volume = 500 sq ft X 8 ft = 4,000 cubic feet

You should now calculate the number of air changes per hour (ACH) you will need to purify your home.

ACH = (CFM X 60) / (Area X Height of Ceiling)

ACH = 15,000 cubic feet per hour / 4,000 cubic feet = 3.75

That means you can exchange the air in a 500-square-foot room 3.75 times with an air purifier that has a CADR of 250.

If you have a very large home with many rooms, then you might want to check out whole-house air purifiers as a solution.

House Coverage

(Sq Ft)

Air Changes Per Hour (ACH)

Number of Air Purifiers Needed

800 sq ft



800 sq ft



1,600 sq ft



1,600 sq ft



3,200 sq ft



3,200 sq ft



How To Choose The Right Size Air Purifier For The Room Size

To determine the square footage of a room, you need to measure the length by the width to get its square footage.

Once you have the square footage, you need to identify the clean air delivery rate (CADR) you will need to purify the space.

To determine this, you need to multiply the room size by two-thirds. Let’s look at an example.

300 (Room Size) X ⅔ = 200

This means you will need an air purifier CADR rating of 200 to purify a room that is 300 square feet in one hour.

Small Rooms

This includes small bedrooms, bathrooms, and personal working spaces. You should look for a desktop or tabletop air purifier.

You will need a small air purifier to cover about 200 square feet. 

TL;DR: We recommend finding a unit with a CADR rating of about 133 or more for small sized rooms.

Medium Rooms

This includes lounges, offices, small basements, dens, or game rooms. It would be best if you looked for a medium-sized air purifier to cover about 201 to 399 square feet. 

TL;DR: We recommend finding an air purifier with a CADR rating of 133 to 266 for medium sized room.

Large Rooms

This includes large living rooms, master bedrooms, offices, and larger-sized basements. You should invest in a large air purifier to cover about 400 square feet or more. 

TL;DR: We recommend buying an air purifier with a CADR rating of 266 or more for large sized rooms.


There are many different types of air purifiers. We recommend mechanical air purifiers with HEPA filters and activated carbon to get best results. 

types of air purifiers

Factors That Affect Air Purifier Effectiveness In A Home

Square Footage of the House

In general, the more square footage you have, the more air purification power you will need.

If you have more space, then you might need to invest in a larger air purifier or get more air purifiers.

Number of Rooms

I have a large, open-plan home, so I use one large-capacity air purifier for the space. The fewer walls you have, the more an air purifier can circulate air throughout the room.

You will only need an additional air purifier if you have a closed floor plan.

Airflow and Size of Air Purifier

Typically, larger air purifiers will work more effectively to increase airflow throughout the room.

The airflow rate of air purifiers is measured in cubic feet per minute (CFM). The higher the CFM, the more clean air the purifier will move.
where to place air purifier

Air Changes Per Hour

The term ACH refers to the amount of air volume that is added to or removed from an area in one hour, divided by the volume of the room. 

This term is used to discuss how many air exchanges per hour an air purifier can provide.

Air Quality

do air purifiers help with allergies

If you have a lot of contaminants in your home, then you will need a more powerful air purifier.

Whether you have smoke, pet hair, or odors, you will need a larger air purifier to clean the space.

You might need more than one per area if you are dealing with a lot of pollutants.

TL;DR: There are many factors including the size of the room, number of rooms, and the airflow capacity of the purifier that decide how many air purifiers you need.

How Many Plants Do I Need To Purify The Air?

In 1989, Bill Wolverton, a NASA scientist, conducted a study on the number of plants needed to purify the air in an area.

According to Wolverton, you should have two good-sized plants for every 100 square feet.

The bigger the plant and the more green leaves it has, the better it will purify the air. Some of the best houseplants for purifying are Chinese Evergreen, Spider Plant, and English Ivy.

How to purify air in home naturally


Although plants can be effective, they cannot replace a high-quality purifier.

TL;DR: Plants can be used in conjunction with Air Purifiers to improve the AQI. However, plants alone are not sufficient for very dirty environment.

People Also Ask (FAQs)

How Many Hours Should An Air Purifier Run to Effectively Clean The Air?

The number of hours an air purifier should run to effectively clean the air depends on the number of contaminants and the size of the room.

If you are experiencing excessive odors, smoke, or pet hair, leave your air purifier on the highest setting for at least 24 hours to cycle the air thoroughly.

Are Two Air Purifiers Useful In The Same Room?

Two air purifiers are only useful in the same room if it is a large open room. You can also move a single air purifier around to clean the air in other parts of the room.

Several air purifiers are only needed for extra large areas.

Should I Get An Air Purifier With a HEPA Filter?

Yes, getting an air purifier with a HEPA filter is recommended as it can effectively capture and remove small airborne contaminants from the air, including allergens and pollutants.

Can a Whole-House Air Purifier Clean An Entire House?

Yes, a whole-house air purifier could clean an entire house. Unlike individual room purifiers, whole-house air purifiers offer comprehensive air-cleaning solutions for your entire home.

Can An Air Purifier Be Too Big For A Room?

An air purifier could be too big for one room. Large air purifiers mean better air cleaning efficiency, but they are unnecessary for small rooms and will take more energy to clean the air.

Should I Leave My Air Purifier On When I’m Not Home?

You can leave your air purifier on when you’re not home. Most air purifiers are energy efficient, so you can leave them on when you are not home and not spend a ton of extra money on utilities.

Where Should An Air Purifier Be Placed In A Room?

Your air purifier should be placed away from all obstructions in a room. Ensure no obstructions are covering the ventilation areas on the purifier.

Areas with the highest airflow, such as doorways and window areas, are ideal.

Number of Air Purifiers = Size Of Your Room

After seeing countless instances of one air purifier working too hard or multiple air purifiers not doing anything, I can certify to the importance of determining how many air purifiers you need.

Remember that no matter how good an air purifier may be, it cannot clean a space larger than its capacity. 

Therefore, it is crucial to choose the right number of air purifiers based on the size of your room.

Fortunately, by installing the appropriate number of air purifiers in your home, you can ensure that your indoor air quality is consistently at its best.

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Josh Mitchell


Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

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Midea U Shaped Window Air Conditioner

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