Small Air Purifiers

small air purifiers

Four different “sizes” of air purifiers dominate the market:

Super SmallNo taller than about 10 in.Under 5 lb.Often called desktop air purifiersUsually output at well under 100 CFMCannot be used in spaces larger than around 60 to 70 sq. ft.
SmallEither about 22 in. tall but less than 10 in. wide and deep - i.e. small towers - OR about 12 to 17 in. tall and about 10 in. wideUnder 10 lb. Usually output at right around or slightly above 100 CFM Can be used in rooms up to about 150 sq. ft.
MediumAbout 18 to 24 in. tall, 15 in. wide, and 10 in. deep at mostAbout 12 to 16 lb.Top rated units we recommendUsually output at least 200 CFM - most around 250 CFMCan be used in rooms up to 300 sq. ft.
LargeMore than 24 in. tallHeavier than 16 lb. Output varies - some have more CFM than medium units. Some have just as much or less.Area of coverage varies also but our testing has shown that no matter the CFM, a single air purifier shouldn't be used in a space larger than 300 sq. ft.

We generally do NOT recommend super small or small air purifiers. To explain why, let’s take a look at each of the air purifier sizes we laid out above, one at a time.

Super Small

Example models: GermGuardian AC4100 and LEVOIT LV-H126

These air purifiers are very small. Again, most are 10 in. tall or less and weigh less than 5 lb. They’re air processing power is also very small – usually around 50 CFM which makes them appropriate for rooms no larger than 60 to 70 sq. ft.

Many consumers believe that they can use a super small desktop air purifier in a large room, as long as the air purifier is right next to them and/or pointed directly at them. They believe that the air purifier will clean the air immediately surrounding them. Or, if it’s pointed directly at them, that it will blow clean air onto them for them to breath in.

The truth is that this is simply not the case.

Unless you’re putting your nose or mouth right up to the grill of the air purifier, you’re not breathing in 100% cleaned air.

Remember, air is a gas and gases tend to go to equilibrium – and quickly.

So as soon air with low particle concentration leaves the air purifier, it spreads out into the room immediately – faster than you’re able to breathe it in. At the same time, air with higher particle concentration swoops in. All of this happens extremely quickly.

So no, you absolutely cannot expect to put an air purifier directly in front of you or near you and expect it to clean the air you’re breathing in.

It will, over time, lower the total particle concentration in the whole room. But unless the room is extremely small – well under 100 sq. ft. – these units will not be able to lower particle concentration properly. *

They only process air at a rate of about 60 to 70 CFM (cubic feet per minute) at best. And this is only good enough for rooms up to about 80 sq. ft.

Our Recommendation

The bottom line here is that we simply don’t recommend this size air purifier. Not only can it only be used in extremely small spaces – spaces smaller than what’s needed for the vast majority of applications (most rooms are larger than 80 sq. ft.)  – but it will also need to run at maximum fan speed to do so.

At maximum fan speed these units run very loudly and exhibit poor energy efficiency. At lower fan speeds (and therefore lower CFM) these units do next to nothing to lower particle concentration in even the smallest room. This means that at acceptable noise levels and with better energy efficiency, these units have no use at all.

* If the room is small enough and the particle concentration is high enough a super small unit can certainly lower concentration in the room to a certain extent given enough time. But our testing has shown that even after running these units for several hours they still fail to reach acceptable lower thresholds.


Example models: GermGuardian AC4825, Blue Pure 411, and Honeywell HPA100

We classify small air purifiers as units that are either tall but thin or small all-around but not as small as super small units and not as large as medium sized units. Units in this category tend to output in the 100 to 120 CFM range – sufficient output for rooms up to 150 sq. ft.

Some examples of specific models in this size category include:

1. GermGuardian AC4825

This is an example of what we call a “small tower” air purifier. It is fairly tall but it’s not very wide or deep and it’s very light – weighing right around 8 lb.

This unit outputs at about 130 to 140 CFM.

2. Blue Pure 411

This unit features a cylindrical shape with inputs on the bottom and an outlet up top. It’s a little over 16 in. tall with an 8 in. diameter. It only weighs about 3 lb. It outputs at around 120 CFM.

3. Honeywell HPA100

This unit features a more traditional design. It’s about as tall as it’s wide – about 14 in. It weighs around 8 lb. and outputs right around 110 CFM.

Units in this size category are still very small and light but offer much better output than super small units – enough for rooms up to 150 sq. ft. which is a much more reasonable room size that makes these units a potential good fit for many different applications.

Units in this size category usually retail for around $100 which is also a big reason for their appeal. They’re very affordable.

Our Recommendation

Despite the fact that these units are a decent value and can certainly accommodate a reasonably sized space up to 150 sq. ft. we still do not recommend them. We go over the reasons why in the next section as we compare small air purifiers to medium sized units.


Example models: Winix 5500-2, Coway Mighty

What we classify as medium sized units are no taller than 24 in. no wider than 15 in. and no deeper than 10 in. They tend to weigh around 15 lb. and output in the 200 to 250 CFM range – sufficient output for rooms up to about 300 sq. ft.

Medium sized air purifiers really are not that much larger than small air purifiers. Yes, you may need to put medium units on a floor while you can easily put a small air purifier on a table. But most medium sized units are still small enough to comfortably be used even in a smaller bedroom.

And by going up in size and weight ever so slightly, you get about double the output of a small air purifier. Medium units can be used in rooms as large as 300 sq. ft. while small air purifiers cannot be used in rooms larger than 150 sq. ft.

Our Recommendation

Medium units can certainly service larger rooms up to 300 sq. ft. but they can be used even more effectively in smaller rooms in the 150 to 200 sq. ft. range.

In such a size space – such as in a smaller bedroom – medium sized units tend to be much more effective and much more efficient than small air purifiers.

Here’s what we mean:

A small air purifier has to be run on maximum fan speed to properly accommodate even a small room up to 150 sq. ft. On these max settings it usually draws a substantial amount of power and produces a lot of noise as well.

A medium sized air purifier can be run on a lower fan speed at the same output. On this lower setting it runs extremely energy efficiently and most importantly, it makes very little noise.

In other words, a top rated medium sized unit like the Winix 5500-2 can be run on its second highest setting to output at approx. 100 CFM. A small air purifier like the Honeywell HPA100 has to be run on its highest setting to output at approx. 100 CFM.

At an output of approx. 100 CFM the Winix is very quiet (because it can be run on a lower fan speed) and highly energy efficient. The Honeywell, on the other hand, is much louder (because it has to be run at max. fan speed) and much less energy efficient.

So not only do you get the added versatility of being able to use a medium sized unit in a larger space, but it actually works better in smaller spaces as well.

You may have some questions about this recommendation so let’s address some potential criticisms you may have:

You may say that

"a small air purifier is cheaper to buy"

Yes, but you also get less for that lower price. You get less output and you often get worse filters. Cheaper smaller units usually have HEPA filters just like the larger units we recommend so particle filtration is going to be similar on both units. However, cheaper smaller units often have much worse carbon filters than larger units. This means that you’re likely going to get much worse gas filtration (to remove odors and VOCs) with smaller units.

Not to mention the fact that you often get worse energy efficiency with a smaller unit. Over time, you’re going to be paying more in energy costs to run the small unit at the same output as running the larger unit on a lower setting.

You may say that

"a small air purifier also has cheaper filters"

Yes, but the filters are also much smaller.

If you run an air purifier equipped with a filter with a surface area of 60 sq. in. and an air purifier equipped with a filter with a surface area of 120 sq. in. – all other things being equal, including the CFM you’re running on both units (max fan speed on the small and lower on the large) and the total number of particles in the air – the smaller filter is going to saturate twice as fast as the larger filter.

The end result? You’re going to need to replace it twice as frequently – and that all but takes care of the cost disparity concern you may have.

Our bottom-line recommendation regarding small air purifiers

Our recommendation is that you buy a medium sized unit. You’re going to be able to run it with maximum energy efficiency and very quietly in a small room. And it’s still going to be very affordable to do so.

Only buy a small air purifier if you absolutely don’t have room for a slightly larger unit. If that’s the case the best small air purifiers we’ve tested so for are the GermGuardian AC4825 or the Blue Pure 411. For most users we would recommend the AC4825 but we recommend you read our review for each of these units to determine which model fits your application the best.

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