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GermGuardian AC4100 Review

A compact model with decent performance that is adequate for small (100 square foot) rooms
Top Pick Award
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Price:   $70 List | $55 at Amazon
Pros:  Low operating costs, low list price, good performance for a compact model
Cons:  Relatively loud, slow
Manufacturer:   Guardian Technologies
By Max Mutter and Steven Tata  ⋅  Jul 8, 2017
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#12 of 14
  • Air Cleaning Performance - 40% 4
  • Noise - 25% 4
  • Ease of Use - 25% 7
  • Operating Cost - 10% 8

Our Verdict

While small and slow the GermGuardian AC4100 is incredibly affordable, making it a great choice for small (less than 100 square foot) rooms, or for occasional use in a guest bedroom. It performed much better than the other small, inexpensive purifiers in our air cleaning tests, earning it our Top Pick for Small Rooms Award. It's only big downside is the noise it makes, which isn't grating, but might annoy those that are sensitive to noise. If that's the case and you're looking for a small air purifier you might want to consider the Holmes HEPA Type Desktop or the Hamilton Beach TrueAir. Both of these small models are quieter, but didn't perform as well in our air cleaning tests.

Compare to Similar Products

Our Analysis and Test Results

While we found small purifiers to generally not perform as well as their larger brethren, the GermGuardian AC4100 was the best of the compact contingent.

Performance Comparison

While the GermGuardian AC4100's overall score was one of the lowest in our testing, it was still the most effective of the small air purifiers that we tested.

Below we dive into the details of how the AC4100 performed in all of the different tests we use to determine our overall scores.

Air Cleaning Performance

The GermGuardian AC4100 was one of the lowest scorers in our air cleaning testing with a 4 out of 10. However, both of the other compact purifiers we tested earned 3's.

After 30 minutes in a smoke filled room the AC4100 had managed to reduce airborne particulate counts by 83.83%. This was far off from the best performers, which had reached upwards of 99% at the same point, but much better than the other compact models which hovered in the high 70's. At one hour it had eliminated 95.32% of airborne particles. The other compact models had only reached about 89% at the same point in their testing. Bottom line, the AC4100 is fairly effective at air cleaning, but it is slow. Its CADR rating of 64 only makes it suitable for rooms of 100 square feet or less. It would likely be able to clean the air effectively in a larger room if you let it run for a couple of days. This is why we suggest it for guest bedrooms. If your guests have allergies you can run it for a couple days before they get there and hopefully give them some good sleep while they visit. In terms of odor reduction the AC4100 did very little in our testing, with almost no appreciable change in our testing room's smoky musk.

Considering its compact size  the AC4100 performed quite well in our air cleaning tests.
Considering its compact size, the AC4100 performed quite well in our air cleaning tests.


The AC4100's biggest drawback is the noise that it produces. Accordingly, it earned one of the worst scores in our noise testing.

What really knocked the AC4100 to the bottom of our noise scoresheet was the high pitched moan it produces on its high setting. It's not overpowering but is quite hard to ignore. Reeling the AC4100 back to its medium and low settings doesn't really lower the volume too much, but the pitch gets a little bit lower. This is better, but still very noticeable. If you're the kind of person that doesn't mind running the dishwasher while you watch TV or eat dinner, you probably won't mind the sound of the AC4100, and it may actually serve as some nice white noise when you're sleeping. If you're sensitive to noise, however, you may want to opt for a quieter model.

Ease of Use

The AC4100 was a bit above average in our ease of use testing, earning a score of 7 out of 10.

The AC4100's controls are nearly identical to those of its larger sibling, the AC4300BPTCA. It has a single dial to select from three fan speeds, and a single button to turn its UV lamp on and off. That UV lamp is meant to kill airborne bacteria. While there is evidence that industrial UV air purifiers in hospitals can be beneficial to patients, there isn't any conclusive evidence that the same technology is effective in small home purifiers. The AC4100 lost some points because most models offer more fan speeds (4-10) and offer automatic off timers, so you don't accidentally leave it running in an empty house all day. It also lost some points because it did create a faint plastic smell for the first few hours that we ran it, but that smell eventually dissipated. It gained some points because, at just 5 pounds, it is incredibly easy to move around.

The AC4100's controls consist of one knob and one button.
The AC4100's controls consist of one knob and one button.

Operating Cost

The AC4100 was one of the best performers in our operating cost testing. We estimated its lifetime cost to be just $294 over 5 years.

The AC4100 achieved this low lifetime cost with economical pricing in every aspect. Its list price is only $70. Its filters last for 7 months and cost only $19. It also uses electricity fairly economically, requiring only 0.025 kWh of electricity to run for an hour, which translates into a cost of about $13.14 per year.


The value provided by the GermGuardian AC4100 largely depends on how you use it. If you want something for your living room that you're going to use every day, you'd get a much better value spending a bit extra on the GermGuardian AC4300BPTCA. However, if you want something for occasional use, or to just use in a small bedroom during allergy season, the AC4100 provides great performance per dollar.


Compact air purifiers are generally much less effective than large models, but can be adequate, cheap options for occasional use or small rooms. The GermGuardian AC4100 provides the best performance of the compact models we tested and is a great choice for a small bedroom, as long as you don't mind the noise.

Max Mutter and Steven Tata