How Many Air Purifiers Do I Need? 4-Steps Guide To Determine Correct Amount

How many air purifiers do I need? The same question was asked by Eli, our content researcher internee, last week. Having years of experience in environmental study, I helped her to find the right number of purifiers for him. Further, I decided to share my experience with my readers in the form of a guide. Give a thorough read to know about the optimum number of purifiers. Let’s head on to the next section!

how many air purifiers do i need

Quick Answer

Simply put, here’s a breakdown of the number of purifiers based on different scenarios. Let’s check them out:

  1. For a studio or a one/two-bedroom apartment, get one air purifier and for bigger residences, go for one purifier per room.
  2. A rule of thumb is to choose a purifier that has a CADR value of at least two-thirds of the total area.
  3. Ideally, anything above 500 sq ft requires multiple units if you are going for 4 ACH.

However, the above is just the tip of the iceberg. Continue reading below, where I have shared the 4-step method to calculate the exact number of purifiers. Further, I will discuss 6 factors that can help you make the right decision. So, let’s dive in!

6 Factors Guide to Finding the Best Number of Purifiers You Need

The following are 6 factors that you can consider while choosing the best number of purifiers for your needs. When Eli was struggling to find the optimum number of purifiers, this guide of mine helped him a lot. You can explore more below.

1. Know About Your House Size

The size of the space you are living in plays a pivotal part in determining the number of purifiers:

  1. If you opt for a low number of purifiers, you won’t be able to get pure air.
  2. In contrast, a high number of purifiers will cost you more electricity. 

You can either get an idea from your broker about the space or measure it manually with the help of a measuring tape. With the space size in mind, search for air purifier models that have CADR ratings suitable for that size. This will help you narrow down your options and find the right one for your needs.

How to Calculate it?

As a general rule of thumb, know how much CADR is rated for a certain square footage. Just multiply the amount by 1.55

CADR x 1.55 = Square Footage of Room

Here is a little example of understanding the concept. If you have a room of 200 sq ft. The required CADR rating would be at least 129.

Know About Your House Size

The following table can quickly relate the space to the required number of purifiers:

Space (Square footage)

No. of purifiers


1 Unit of 150 CFM


Two air purifiers with a total CFM of 300 - 500


2-3 units with a total of 600 CFM or higher

< 1500

Get a HEPA device for each room with a CFM of 350-500 each

> 1500

Invest in an HVAC system

Pro tip: If you don’t have the resources to purchase an HVAC system, then go for an air filter for every room.

2. Headcount Matters

Along with the space of the house, the number of individuals also plays a role in defining the number of purifiers for a home. The following tips can help you in this regard:

  1. You might only need a single cleaner if you have one or two people;
  2. If you live with a family of 4 or more, a good idea would be to get an air purifier in every room for the best coverage;
  3. If your house has multiple kitchens, I would suggest one purifier for each kitchen.
How many air purifiers do i need - Headcount Matters
Pro-tip: Another alternative to placing a unit in each room would be installing an HVAC system.

3. The Type of Problems You Want to Address

Let’s look at a quick breakdown of what kind of issues you might be facing and the types and numbers of purifiers you need for them:


Best Air Purifier

If you suffer from Allergies

True HEPA Filters Air Purifier

If VOC, Smells, and Odor

Activated carbon filter Purifier

Mold/ Mildew

Prefilter/ UVC Filter Purifier

Pet Dander

High CFM Purifier

Based on the above problems, this is how much air change rate (ACH) you need:



General Use








Important note: If someone at your home has allergies, get an additional device, especially with a medical-grade HEPA filter, to alleviate your respiratory issues. However, if you already have a HEPA-grade filter and need to remove mild mold or VOCs, then you should get a device that has HEPA, pre-filter, and activated carbon filters.

4. Noise Issues

More air purifiers produce more noise while operating. On average it is from 50 dB.

Noise Issues

If you have any issues with this noise, I have listed a few points that can help you in this regard:

  1. If you are a light sleeper like Eli, get a model like Levoit Desktop that operates at 28dB in sleep, and as per WHO, 30 dB of background noise is unnoticeable.
  2. Purchase UVC filter purifiers as they do not need a fan for cleaning but rely on ultraviolet infrared lights. 
  3. Get particular devices that come with sleep and night modes to allow the lowest decibel produced so you don’t get disturbed.

5. Room Ventilation

If the air in your home feels not so fresh, it can be due to your home doesn’t get enough air movement. To tackle this situation, I would recommend choosing an efficient air purifier like a Blueair 211+ will help in this regard. It has a CADR of 350 CFM and can change air around 4 times in an hour which will cater to the ventilation issues with ease.

6. Budget

You should expect to spend a budget of at least $150 on a single unit. If you need an air purifier of high quality, you will have to spend $400-1000 per device. Get help from points to scrutinize the models as per your budget:

  1. So, if you have around 2 bedroom apartment with an area of around 1000 sq ft, then you will have to get 2-3 units with a combined CFM of 600 that will cost you $1000 – $1500 on average.
  2. While some cleaners only cost $50, investing in quality over a second air purifier is better so they last you a lifetime;
  3. If you want to go for HVAC for your entire home, then they will cost at least $6k.

An Insight Into The Best Positioning for Your Air Purifier

Now, you do have an air cleaning system for your home. But how to set it properly? The first thing is to keep the device away from walls and secondly place it near the pollution source for effective cleaning. Also, it is important to keep the purifier away from the heat source.

An Insight Into The Best Positioning for Your Air Purifier

For detailed info on strategic positioning read this guide on the best place to put an air purifier and get the maximum from your device.

Can I Placе Multiplе Air Purifiеrs in a Singlе Room?

Yеs, you can placе multiple air purifiers in a singlе room if thеy don’t intеrfеrе with еach othеr’s flow. But hеrе arе a fеw things to considеr:

  1. You nееd to sее thе layout and sizе of thе room bеforе placing another unit in thе room.
  2. Sее if thе covеragе and capacity of onе unit arе sufficiеnt for that particular spacе.
  3. Thе lеvеls and typеs of pollutants prеsеnt in thе room.

If you have a room with a littеr box, smoking arеa, and kitchеnеttе, placing еach unit to combat thе sourcе would be a good idea. Hеrе arе thе gеnеral critеria for thе air-clеaning dеvicе:

  1. It is bеttеr to gеt onе largе purifiеr than multiplе small onеs that may not bе as еfficiеnt.
  2. You nееd to sее that thе dеvicе can achiеvе at lеast 4 ACH in thе room, mеaning it can clеan thе air еvеry 15 minutеs.
  3. If this is not thе casе, thеn consider upgrading to a large purifiеr or adding another one.
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Can I Place a Single Purifier for Multiple Rooms?

The short answer is yes. However, it also depends on the capacity and power of the running device. Some purifiers are designed for large, open-space rooms with an area of up to 1500 sq ft with a high CADR (Clean Air Delivery Rate) of 350 -500 CFM and around 4 ACH (Air Changes per Hour). If you live in a studio apartment or two-bedroom house, these might work effectively, but not for larger houses.

For multiple floors or larger homes, you have the following options:

  1. Whole home Air Purifier: These are equipped in your HVAC system to capture dust, particles, and pollen from all rooms and provide greater coverage.
  2. Central Air Purifiers: These are stand-alone units with high CADR and ACH connected to the HVAC system and have their filters and fans. But on the downside, they can be a bit expensive.
  3. Portable air purifiers: The last option is to go for a small movable unit like AEROEVE or Levoit Core 300 that you can use around the house. One option is buying one device you use throughout the problem spots. The second is to purchase one for each space/room or floor to improve indoor air quality.
Can I Place a Single Purifier for Multiple Rooms?

4 Steps to Calculate the Total Number of Air Purifiers You Need

Now, we are getting the real deal. After the above discussion, you might want a short yet descriptive answer that can guide you to the exact number of purifiers without any fuss. Don’t worry. Let me end the debate by providing you with a simple formula.

4 Steps to Calculate the Total Number of Air Purifiers You Need

You can calculate the no. of air purifiers needed by these steps:

Step 1: Calculate the Volume of the Room – Multiply the coverage area by ceiling height.

Example: Coverage = 100 sq. ft. Ceiling Height = 8 ft.

Volume = Coverage Area x Ceiling Height = 100 x 8= 800 cubic feet

Step 2: Calculate the Air Moved Per Hour – Multiply the CADR (Clean Air Delivery Rate) by 60.

Example: CADR = 100 CFM

Air Moved/ Hour = CADR x 60 = 100 x 60 = 6000 cubic feet

Step 3: Calculate the ACH – Divide the Air moved per hour by the volume of the room.

Example: Air Moved/ Hour = 6000 cubic feet and Volume of Room= 800 cubic feet

ACH = Air Moved Per Hour /Volume of Room = 6000/800 = 7.5

Step 4: Calculate the number of most air purifiers needed – Divide the desired ACH by the ACH of one single air purifier.


If your desired ACH is 4, then, Desired ACH= 4, ACH of one purifier = 7.5

No. of purifiers needed = 4/7.5 = 0.53

Rounding off to the nearest digit, we get:

No. of purifiers needed ≈ 1

Thus, for a room of 100 sq ft with a height of 8 ft and 100 CFM, you will need one purifier for 4 ACH.

I know all these mathematics might be going all over your head. Therefore, I have done the homework for you and have determined the exact number of purifiers based on your ACH and area: 

Coverage Area


Number Of Air Purifiers Needed

100 sq ft



100 sq ft



100 sq ft



300 sq ft



300 sq ft



300 sq ft



500 sq ft



500 sq ft



500 sq ft



800 sq ft



800 sq ft



800 sq ft



1000 sq ft



1000 sq ft



1000 sq ft




How many air purifiers does your home need?

Ideally, your home needs one air purifier for one room or one floor especially if they are designed for bigger spaces. But you can calculate how many air purifiers your home needs by dividing the ACH of one air purifier by the desired ACH to get the exact number for the best indoor air quality.

Should I get 2 air purifiers?

You should get 2 purifiers if your targeted space is more than 500 sq ft. Otherwise, invest in only a single device that has a CFM of up to 150.

Can 1 air purifier do a whole house?

Yes, 1 air purifier can do a whole house. There are powerful purifiers designed for larger rooms and open floor plans with high CADR measures. But do put a close eye on its effectiveness and coverage capacity and whether it suits your needs.

Can you have 2 air purifiers in one room?

Yes, you can have 2 air purifiers in one room. But keep in mind your budget, the space of your room, and the capacity of each purifier device.


Summing it up, how many air purifiers do I need? You should go for at least one purifier for each room or at least one unit for each floor. If you have a larger space of up to 1500 sq ft, try investing in a large room air purifier that has a CFM of more than 350 or an HVAC system with a stand-alone purifying unit to get the desired air purification.

To calculate the number of purifiers needed, you need to calculate the amount of air volume and divide it by air moved per hour to get the ACH of one unit. Then divide it by the desired ACH you want to get the magic number of purifiers needed for your space.

While adding more than one purifier, you should also consider the coverage capacity and CADR of your units. Look at the level of air ventilation, the types of pollutants and contaminants you want to get rid of, and how many people are using it.