How Many Air Purifiers Do I Need In My House?

A friend of mine has recently asked me: “So, how many air purifiers do I need in my house?”. The answer is not that simple. The ideal number of air purifiers that will adequately cover your entire home or one room will depend on two things: the capacity of the purifiers and the size of the area you want to cover. Let’s talk about each.

Air Purifier Capacity

This is one of the most important factors to consider when choosing an air purifier. The larger its capacity the bigger an area a single air purifier can cover.

There are three types of units used by manufacturers to describe the capacity of their air purifiers. They are CADR (Clean Air Delivery Rate), CFM (Cubic Feet per Minute) and ACH (Air Changes Per Hour).

CADR refers to the amount of purified air that is delivered by an air purifier. It’s measured in cubic metres per hour. The higher the CADR the more powerful the air purifier.

You’ll sometimes find different CADR measurements for different types of pollutants. For instance, a certain air purifier can have a dust CADR of 137, a tobacco smoke CADR of 112 and a pollen CADR of 153.

ACH refers to the number of times the entire air in an enclosed room is filtered in an hour. The number usually ranges between 2 and 5. ACH is an important measure because it tells you how quickly an air purifier works.

If an air purifier has an ACH of 2, it means it filters the air in the room once every half hour. If the ACH is 4, it filters all the air once every 15 minutes.

This variation makes all the difference for people with allergies and respiratory problems such as asthma.

CFM is actually one of the measurements used to calculate ACH. It simply refers to the number cubic feet of air that an air purifier can filter in a minute. The higher the CFM the higher the ACH and the more powerful the air purifier.

In most cases however, understanding these units is pointless. Most manufacturers don’t list the ACH, CFM or CADR of their units. What they do instead if provide a room size guideline.

So if you want to know the number of air purifiers you need, compare the area of the room (or rooms) you want to cover to the maximum usage area recommended by the manufacturer.

Coverage Area

The best way to determine how many air purifiers you need is to measure the room you plan to use it in. Just measure the two perpendicular walls and then multiply the measurements to get a square footage.

If it is an open plan area, make sure you measure the entire space. If you want an air purifier that will cover multiple rooms, simply add up the square footages of each room. If it’s for the entire house, use your home’s square footage to pick the right purifier.

When you go to shop for a purifier, check the maximum usage area recommended by the manufacturer. It is important that you stay under that figure.

If you use a 200 sq. ft. air purifier in a 500 sq. ft. room, it is not going to struggle to purify the air. Staying within the recommended range ensures the purifier provides enough air changes per hour to actually keep your indoor air clean.

If you have a large room, say 500 square feet, either go for a higher-capacity purifier labelled with that square footage or use two mid-size air purifiers.

But don’t go to the other extreme and buy an air purifier that is too powerful for the room size. A 500 square foot air purifier in a 150 square feet room will just be a waste of energy.

If you want to purify multiple rooms at the same time, it’s better to buy an air purifier for each room. It will be more efficient cleaning the air within a single room compared to multiple rooms.

You can also just buy one air purifier and use it in whichever room you are using at the moment. Most air purifiers are compact and light enough that you can move them from room to room.


CADR, ACH and CFM are more precise measurements of air purifier capacity and performance. But since they are not commonly shown on air purifier product descriptions, you just have to go with the shown maximum coverage area.

Unless you want to cover several rooms at the same time, a single air purifier is usually enough. You just have to select the correct capacity. Choose between compact air purifiers (under 200 square feet), mid-size air purifiers (200-400 square feet) and high-capacity air purifiers (500 square feet and over).

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