Informational Guide

How Many Air Purifiers Do I Need? (Room Size Calculator)

In this guide, we help you decide how many air purifiers you need for your home, depending on room size, airflow rating, budget and other factors.

by Josh M

According to the EPA, indoor air pollution can cause fatigue, dizziness, headaches, irritation, and respiratory diseases. One way to combat indoor pollution is to buy an air purifier, but how many do you need? What if you need to purify more than one room?

Check out our guide to figure out how many air purifiers you should buy to keep your indoor air clean.

Recycle Graphic
  • 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.
  • Number of Rooms
    If you have a large, open-plan home, then you should use one air purifier for the space. The fewer walls you have, the more an air purifier can circulate air throughout the room.
  • 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.
  • Air Quality
    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.
  • 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.

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. 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 with a CADR 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. We recommend finding a unit with a CADR rating of about 133 or more.
  • 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. We recommend finding an air purifier with a CADR rating of 133 to 266.
  • Large Rooms
    This includes rooms such as 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. We recommend buying an air purifier with a CADR rating of 266 or more.

How Many Air Purifiers Do I Need For My House?

The two main factors that will determine how many air purifiers you need in your home are the square footage and the airflow or capacity of the air purifier. Keep in mind, you might not necessarily need an air purifier for every room, but you can move one around to circulate the high traffic areas.

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 4 2
800 sq ft 2 1
1,600 sq ft 4 4
1,600 sq ft 2 2
3,200 sq ft 2 4
3,200 sq ft 1 2

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. Learn about natural home purification here.

A Kid Planting a Seedling

People Also Ask (FAQ)

How many hours should an air purifier run to effectively clean the air?

It depends on the number of contaminants and the size of the room. If you are experiencing excessive odors, smoke, or pet hair, then we recommend leaving 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?

You will only need two air purifiers in the same room if you are dealing with an ample space. You can also move a single air purifier around to clean the air in other parts of the room.

Can an air purifier be too big for a room?

Yes, technically it’s possible for an air purifier to be too big for a room, although nothing bad will happen if this is the case. It just means that more energy will be used to clean the air than if a smaller air purifier was used. So if you want to use a purifier that’s oversized then it’s fine to do so.

There’s a couple benefits to getting a smaller one though. Firstly, smaller purifiers are cheaper to buy and use less electricity, saving you money on energy costs.

They are also quieter in general which may help if you’re running it in the bedroom while sleeping.

Should I leave my air purifier on when I’m 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. We recommend this if you have pets at home or keep your windows open. We have covered this in a separate article on running an air purifier.

Where should an air purifier be placed in a room?

You should place your air purifier in the area with the most pollutants. You should ensure no obstructions are covering the ventilation areas on the purifier. We also recommend putting it in areas with the highest airflow, such as doorways and window areas.


At Air Conditioner Lab, our goal is to provide you with the most up-to-date information on the best HVAC products. In this guide, we have helped you decide how many air purifiers you need for your home, depending on room size and airflow rating.

Last Updated on April 11, 2022

Josh M

My name is Josh and I am obsessed with the HVAC industry. I created this website to help HVAC techs of all levels get the best out of their heating & cooling systems. I have spent thousands of hours studying air conditioners, heaters and home air products so you can learn & buy with confidence. Learn more about the team here.