How Many Air Purifiers Do I Need?

When I was looking for the right kind of air purifier to buy for my own home, I noticed just how different their capacities were. Some were able to only purify the air in one small room, while others promised to purify the air on the entire floor of my house.

So, how many total air purifiers do you need in your home? Generally speaking, it’s best to have an air purifier in the rooms where you spend the most time. This may mean needing at least 3 air purifiers – one for the living room, one for the kitchen, and one for the bedroom. You’ll also need to use CADR (clean air delivery rate) specifications to make sure each air purifier has the capacity to move and filter all the air in each room.

Interestingly, you can’t take each of the manufacturer specifications at face value. There are a few other factors to consider to truly find the air purifier that’s best for you.

You May Need Quite a Few Air Purifiers

Wouldn’t it be great if we could buy one inexpensive, portable air purifier and it could purify the air in an entire house? Unfortunately, it doesn’t work that way.

At the same time, buying too many cheap air purifiers isn’t the solution, either. They’ll just break down after about a year and end up being a drain on your energy bill. Some may do little to even clean the air. The key is to find just the right air purifiers and to match them to each of the most important spaces in your home.

Break Down Your Home Into Areas

It doesn’t make sense to buy the same air purifier for every single room. You’ll first need to assess how large each space is, as well as what exactly you need to do. Here is a sample worksheet for my home and the thoughts I had when I began this process.

Area	Total volume (ft³)	Needs
Open living, dining, kitchen, and foyer	4,200	Large area. May need 2 air purifiers or more. Definitely want a heavy activated carbon filter to catch the odors while cooking. True HEPA filter that blocks out fine particles coming from front door and patio door.
Master bedroom	1,600	Want a low-noise air purifier. Has to have the ability to turn off the light display. Must catch VOCs – we will be renovating this room soon. True HEPA filter would be nice.
Baby nursery	950	Has to be tabletop and out of reach. Low noise. Concerned with fine particles, filters need to filter 99.7% or more – must have True HEPA filter. Light display is not an issue.
Basement	2,100	Want to have a low-maintenance system that will work with the dehumidifier to prevent mold. Must catch carbon monoxide since basement is attached to the garage.

What CADR Rating Do I Need?

Once you’ve drawn up a plan of where you’d like to have your air purifiers in the home, you’ll want to look for products that have a specific label called the AHAM Verifide label. Administered by the Association of Home Appliance Manufacturers (AHAM), this is a voluntary label that shows that air purifiers have been independently tested.

It’s an industry standard that debunks a lot of the misinformation out there about air purifiers. Since it’s an independent test, this is definitely something to look for on the box of the air purifier before you buy it.

The AHAM tests for something called the clean air delivery rate, or CADR. Its measurement is given as how many cubic feet of air the air purifier is able to take in, purify, and push out per minute while cleaning out 80% of the pollutants in the air per a one-hour cycle.

In simple terms, you want to match the volume of the room to the right CADR rating before you buy an air purifier.

Use the table below to find out what kind of CADR ratings for air purifiers you’ll need for each of the areas in your home.

Room dimensions (ft)	Ceiling height (ft)	Total volume (ft³)	CADR needed in ft³/min*
6 x 6	8	288	23
7 x 7	8	392	32
8 x 8	8	512	41
9 x 9	8	648	52
10 x 10	8	800	65
11 x 11	8	968	78
12 x 12	8	1,152	93
13 x 13	8	1,352	109
14 x 14	8	1,568	126
15 x 15	8	1,800	145
16 x 16	8	2,048	165
17 x 17	8	2,312	186
18 x 18	8	2,592	209
6 x 6	9	324	26
7 x 7	9	441	36
8 x 8	9	576	46
9 x 9	9	729	59
10 x 10	9	900	73
11 x 11	9	1,089	88
12 x 12	9	1,296	105
13 x 13	9	1,521	123
14 x 14	9	1,764	142
15 x 15	9	2,025	163
16 x 16	9	2,304	186
17 x 17	9	2,601	210
18 x 18	10	3,240	261
6 x 6	10	360	29
7 x 7	10	490	40
8 x 8	10	640	52
9 x 9	10	810	65
10 x 10	10	1,000	81
11 x 11	10	1,210	98
12 x 12	10	1,440	116
13 x 13	10	1,690	136
14 x 14	10	1,960	158
15 x 15	10	2,250	181
16 x 16	10	2,560	206
17 x 17	10	2,890	233
18 x 18	10	3,240	261

(*The calculations in this table were made using this source document.)

You may need several air purifiers for large spaces since CADR cap off at 400 or 450, depending on which pollutant you’re looking at.

To give you an example, say you have a room that’s 12 by 12 feet and has a 9-foot ceiling. Its volume would be 1,296 cubic feet and you’d need an air purifier with a CADR rating of 105 or above, using the table above. Next, we need to find an air purifier to see if it will work in the example room.

I used the GermGuardian True HEPA air purifier as an example since it’s one of the most popular ones on the market currently. The AHAM Verifide label for it is below.

The AHAM Verifide suggests that the air purifier should work up to 167 square feet. This looks excellent, just keep in mind that this suggestion is for rooms with 8-foot ceilings. My room had 9-foot ceilings, and that’s why I used the table above instead to verify the information.

My room requires a CADR of 105 or above, and the CADR readings on the label for the three pollutants seem like a good match for my room. Each of the three CADR ratings on the label is well above what my calculated CADR needs are.

Pay Attention to the Units of Measurement on CADR

A true AHAM Verifide label should give you the CADR in cubic feet per minute (ft³/min). Unfortunately, many manufacturers display their CADR measurements in cubic meters per hour (m³/h). If you’re not reading the label carefully, you may think that the air purifier can purify a larger area than it really can. If you have a hard time finding the measurements, that’s a good thing. It means that the measurements are in ft³/min.

But if you see m³/h, you’ll need to look more closely.

For example, a CADR of 135 ft³/min is the same as a CADR of 230 m³/h.

Other Things to Consider When Considering an Air Purifier

Unfortunately, just measuring the CADR alone isn’t enough. There are a few things you’ll need to consider before you hit the buy button on your new air purifiers. You’ll need to understand that while the AHAM Verifide program is probably the best known and most trusted in the industry, it has a long way to go to be the be all, end all test.

When manufacturers submit their air purifiers to AHAM for testing, remember that the air purifier is brand new. It’s tested at the highest setting, with new filters. In a real home setting, you may not always use the highest setting. Filters will become full and clogged over time, so it should be expected for the airflow to weaken over time.

All these factors can greatly change the actual CADR once the air purifier is in your home.

And as another caveat to the test, you also should have noticed by now that the CADR is given for three pollutants only.

Let’s take a look at each of those caveats and understand what you as a consumer can do about them.

Highest Settings and Brand New Filters

You can’t change filters all the time just so you can maintain peak performance. Nowadays, air purifiers have several filters, not just one. You may have come across product features like 3-in-1 or 5-in-1, meaning that there are quite a few filters that each need to be changed out periodically. This can often cost hundreds of dollars, so it isn’t feasible to change filters constantly.

The next thing you may consider is keeping the air purifier at the highest setting to maintain its peak air filtration performance. This is the ideal setting, but you’ll need to see how loud the air purifier is.

If you can get an in-store demo, you’ll be able to gauge just how loud the air purifier is. If you’re buying the air purifier online, you won’t know how loud the air purifier will be. Most people don’t like to run their air purifier at the highest setting because of the noise. It isn’t terrible, but it is noticeable.

This may not be a concern in your busy rooms where the TV is constantly on, but it’s something you’ll need to think about especially for your bedrooms. Typically, once an air purifier passes about 50 to 60 decibels in noise, most people will have an urge to change it to the lower setting.

There are also air purifiers that are advertised as low noise. You can either purchase those for your bedrooms, or you can just purchase an air purifier with a much stronger CADR rating. That way, even when you turn it to the lower setting, its CADR should be comparable to the CADR your room needs.

What About the Other Pollutants?

The CADR is only given for tobacco smoke, dust, and pollen. This essentially leaves out finer particles, which are mostly about 0.1 to 1.0 micrometers in diameter. Just because a CADR isn’t given for those, however, doesn’t mean that your new air purifier won’t be able to filter many of those particles out. It just means that they weren’t part of the test.

As long as you’re getting the right filters, you should be able to filter most of the air in the room. While it may be great to eliminate even the small, 0.1 micrometer particles, the reality is that for most homes, an air purifier with a True HEPA filter will suffice. It will remove particles 0.3 micrometers and larger, which is roughly 99.97% of the air pollutants in a home.

Also, tobacco smoke is a very small pollutant and is considered to be part of the fine particle group of pollutants (2.5 micrometers and lower). If an air purifier has the capability to effectively remove tobacco smoke, theoretically it should be able to remove many other small particles as well that are comparable in size. Also, an activated carbon filter can help filter out many of the smaller, remaining pollutants. So unless you live in an area high in smog or are worried about filtering out small viruses and bacteria, you should be able to find an air purifier that meets your needs at a reasonable price.

Take a look at the Honeywell line of air purifiers. This one checked off most of my requirements when it was time to find the best air purifier for my home, one of them being a True HEPA filter for my allergies.

Air Quality