Reviews You Can Rely On

GermGuardian AC4100 Review

A compact model with decent performance that is adequate for small (100 square foot) rooms
germguardian ac4100 air purifier review
  • 1
  • 2
  • 3
  • 4
  • 5
Price:  $90 List
Manufacturer:   Guardian Technologies
By Buck Yedor, Max Mutter, and Steven Tata  ⋅  Jun 17, 2021
  • Air Cleaning Performance - 40% 4.0
  • Noise - 25% 4.0
  • Ease of Use - 25% 7.0
  • Operating Cost - 10% 8.0

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 occasional use in a guest bedroom. It offers average performance in the air cleaning metric and performs similarly to other smaller-sized models. The only real problem with this device is the high-pitched noise it makes while operating, which may be annoying to those sensitive to noise.
Low operating costs
Low list price
Good performance for a compact model
Relatively loud

Our Analysis and Test Results

Performance Comparison

germguardian ac4100 air purifier review - the ac4100 is a compact model at an excellent price.
The AC4100 is a compact model at an excellent price.
Credit: Jenna Ammerman

Air Cleaning Performance

The AC4100 is one of the lowest scorers in our air cleaning testing. However, both of the other compact purifiers also earned low scores.

After 30 minutes in a smoke-filled room, the AC4100 reduced 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 the one-hour mark, 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.

The AC4100 did very little in our testing in terms of odor reduction, with almost no appreciable change in our testing room's smoky musk. Its CADR rating of 64 only makes it suitable for rooms of 100 square feet or less. It would likely clean the air effectively in a larger room if you let it run for a couple of days, which is why we suggest it for guest bedrooms. If your guests have allergies, it would be wise to run it for a couple of days before they arrive, so you can provide them with an allergen-free sleeping space.

germguardian ac4100 air purifier review - considering its compact size, the ac4100 performed quite well in our...
Considering its compact size, the AC4100 performed quite well in our air cleaning tests.
Credit: Jenna Ammerman


The AC4100's biggest drawback is the noise that it produces. As such, 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.

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 benefit 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 five pounds, it is incredibly easy to move around.

germguardian ac4100 air purifier review - the ac4100's controls consist of one knob and one button.
The AC4100's controls consist of one knob and one button.
Credit: Jenna Ammerman

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 five years.

The AC4100 achieved this low lifetime cost with economical pricing in every aspect. Its filters last for seven 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 AC4100 largely depends on how you use it. If you want something for occasional use or 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 some of 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.

Buck Yedor, Max Mutter, and Steven Tata
You Might Also Like

Ad-free. Influence-free. Powered by Testing.

GearLab is founded on the principle of honest, objective, reviews. Our experts test thousands of products each year using thoughtful test plans that bring out key performance differences between competing products. And, to assure complete independence, we buy all the products we test ourselves. No cherry-picked units sent by manufacturers. No sponsored content. No ads. Just real, honest, side-by-side testing and comparison.

Learn More