GermGuardian AC4825 Review – Top-Selling Air Purifier

The GermGuardian AC4825 is the bestseller and one of the most popular air purifiers out there. But is it time to move on to something more modern?

Our Verdict





Operating cost


Value for money


Ease of use




The GermGuardian AC4825(E) is an old-fashioned air purifier lacking advanced features and offering small coverage, but it still remains one of the best-selling air purifiers on the market.

It uses a four-stage filtration technology, including a pre/charcoal filter combo, True HEPA filter, and UV-C light. The UV-C light is optional, and its use is not required. Additionally, the AC4825 is CARB-certified, guaranteeing its safety for use.

This air purifier has shown excellent results in performance tests. However, its power rating is a concern (even though it’s Energy-Star rated), particularly when considering the power-to-CADR ratio.

Overall, the GermGuardian AC4825 is an okay air purifier, well-built, and often available at a very low price. If you find it at such a price, it’s worth considering!

What we really like?

  • It performed very well in performance tests, especially in a 194 sq. ft. room, where it improved air quality by about 92%.

  • The GermGuardian offers an impressive 3-year warranty for the AC4825 model.

  • This is still one of the best-selling air purifiers, evidencing high reliability and trust among users.

  • It uses advanced four-stage filtration technology, features minimalistic controls, and is made of good-quality materials.

What could be better?

  • The GermGuardian AC4825 has a relatively low CADR for its price range, limiting its coverage to rooms of only 167 sq. ft.

  • The positioning of the UV-C light isn’t the best, and some research suggests the exposure time of the air near the light is insufficient for the UV-C light to kill bacteria or viruses effectively.

  • Replacement filters are a bit overpriced, but there are plenty of third-party replacement filters available.

Smoke Test Performance

GermGuardian AC4825 - Smoke Test
The GermGuardian AC4825 removed all the smoke from the smoke box in 38s. Photo: / Milan Antonic


ManufacturerGuardian Technologies
Dimensions (inches / cm)9 x 5.5 x 22 inches (22.9 x 14 x 55.9 cm)
Weight (pounds / kg)-
Clean Air Delivery Rate (CADR)-
Filtration TechnologyPre/Charcoal Filter Combo, True HEPA Filter, and UV-C Light
Filter Replacement IndicatorYes
Filter Lifeup to 6 months (HEPA)
Number of Fan Speeds3 – Low, Medium, and High
Air Quality Sensor No
Air Quality IndicatorNo
Auto Mode No
Smart App No
Voice Control No
Other FeaturesN/A
Coverage (4.8 ACH) 167 sq. ft. (15.5 m²)
Performance Ratings
Power Consumption 55W
Operating Costs Ratings
Noise Level (low – high)46.7 – 54.2 dBA
Noise Ratings

Full Review

GermGuardian AC4825 is a simple air purifier that is extremely easy to use. With no advanced features on the control panel, this air purifier is ideal for people who love fresh air but don’t want to be bothered with too many options. AC4825 only has three speeds, but it is a 4-in-1 air purifier. 4 in 1 means that it uses four different cleaning air methods.

I must say that even though it doesn’t have advanced features, the GermGuardian AC4825 air purifier is one of the most popular air purifiers on the market. Without a doubt, this air purifier is one of the best sellers from the Guardian Technologies company.

GermGuardian AC4825 - Air Purifier Review
I put GermGuardian AC4825 on a small desk in my living room. Photo: / Milan Antonic

GermGuardian AC4825 is built for a 167 sq. ft. room. It uses the 4-in-1 filtration system, which includes the UV-C light, which will kill germs and mold spores.

Since the AC4825 air purifier is one of the best sellers, I tested it to check if the gadget is really that good or if its quality also contributes to the fact that it is the best seller or something else. Let’s get started with the main specifications of the GermGuardian AC4825, and you will find out if this device is worth buying and if it really is as well as it goes.


The GermGuardian AC4825 uses a tower-shaped design. This tower-like design is proven to be useful because it can be placed in tight spots. GermGuardian company usually makes air purifiers in this design because they are more practical, especially if you don’t have too much space in your home, office, or anywhere you want to.

GermGuardian AC4825 placed on a very small table.
The GermGuardian AC4825 was placed on a very small table. Photo: / Milan Antonic

I tested a black GermGuardian air purifier, but if you don’t fancy black color, and if a white air purifier would fit better in the interior, you can go for it. This company provided two different colors of this gadget.

The black color is the brand of this GermGuardian model, and almost the whole device is in black. Only the top is in silver color with a blue line that emits light. On top is the control panel. However, there are not many options to use, the UV-C light button and fan speed knob. On the back of the air purifier is also a hole that is used for transport. You can transport it with one hand. The overall design is nothing special.

Control Panel

The GermGuardian AC4825 is pretty straightforward to use as it does not contain many options and keys that could confuse you when using it. There are only a power knob and UV Light button to operate this device.

As already mentioned, the device is turned on with a power knob. By moving the knob in the clockwise direction, you can also control fan speed. AC4825 has three speeds; low, medium, and high

GermGuardian AC 4825 Control Panel, power knob and a UV-C light bulb.
The GermGuardian AC4825 control panel contains a power knob, UV button, and Change Filter Indicator. Photo: / Milan Antonic

By turning the power knob, you also control speed and turn the air purifier on or off. UV-C light button is also a filter replacement button that is used to reset the filter replacement period. 

A button with UV letters is used to turn the UV-C bulb on. This button is also used to reset filters and UV-C light. I will talk more about the reset function later in the review.

In the end, when the air purifier is done with the job, you can turn it off by moving the power knob back into a default position.


The GermGuardian AC4825 has an air inlet on the back, and on the front is an air outlet, so keep that in mind when you want fresh air delivered directly to your face. If you would rather the device not blow right into you, you can turn the device away.

The air outlet is located only on the front side of the device, so you will easily manage it and determine where you want it to blow fresh air. The freshness you will feel after the device cleans the air in your room is inevitable.

Size and Dimensions

GermGuardian AC4825 is tall (9 x 5.5 x 22 inches) but small, with only 8.55lb in weight. It also has a handle on the back for easier transport. You won’t have any problems moving it from one location to another.

The back handle that is used for easy transportation between rooms is slippery, so be careful when moving it.

Accessories and Parts

GermGuardian Company provides you with all the necessary parts for initial use. Be sure you will get all the essential accessories and components that will be used most commonly. 

You will get the GermGuardian AC4852 all assembled and, you can turn it on immediately without any additional actions required. 

All parts and accessories that come in a box are an air purifier, a true HEPA filter, and a pre-filter that is a combination of a pre-filter and charcoal filter. Also, you will get a UV-C bulb and a user manual

Features Overview

Certified Device

GermGuardian AC4825 is a certified device that guarantees quality. It has EPA, CARB, Energy Star, and AHAM certificates. In other words, you can’t go wrong with the GermGuardian AC4825 air purifier if you only look at the certificates.

No Ozone

GermGuardian AC4825 is free from ozone, and that is true! Proof of that is the CARB certificate. Some air purifiers produce ozone, but AC4825 is certainly ozone-free.

Silent at Work

Silence is essential for the bedroom because loud noise can bother your sleep. Don’t worry about this GermGuardian gadget; it is quiet enough, and you will be able to sleep like a baby. Turn the AC4825 air purifier on at the first speed and breathe clean air during the night.

Room Coverage

This GermGuardian model device is built for up to 167 sq. ft. rooms. In the recommended room size, this device will perform best. Below, you will find out how great the GermGuardian AC4825 air purifier performed. However, if you need an air purifier to use in a larger room, you will need a more powerful gadget. In this case, take a look at the Levoit Core 300 model.

GermGuardian AC4825 Air Purifier Placed On Desk
The GermGuardian AC4825 air purifier was placed on the office desk. Photo: / Milan Antonic

The UV-C bulb is turned off by default, if you are suspicious about UV-C light function, you never have to turn it on.


A three-year warranty from GermGuardian is more than generous. However, you will need to register your device on the GermGuardian website to use the full three-year warranty. But I have to emphasize that the warranty doesn’t apply to the filters or the UV-C bulbs. We should purchase them on our own. 

It Can be used in combination with a smart plug. But you will need to turn on the UV-C light manually, as the AC4825 does not remember if the UV-C light was on after the device was turned off.

Room Coverage and CADR

CADR ratings are the way you can see the difference between the filtration power among air purifiers. Each rating is important, and you can pick an air purifier that best fits your needs. 

Smoke 108
Dust 118
Pollen 125

For example, if you have smoke or odor trouble at home, then look at CADR for a smoke. Check out the table below with all the CADR ratings of GermGuardian AC4825.

The GermGuardian AC4825 is intended for rooms up to 167 sq. ft. and will fit the living room, bedroom, or any other room in the above-mentioned dimensions best.

How does the room coverage of the GermGuardian AC4825 compare to other similar air purifiers?

DeviceSuggested coverage (sq. ft.)
GermGuardian AC4200Wup to 105 sq. ft.
Winix 5500-2up to 360 sq. ft.
Levoit Core 300up to 219 sq. ft.
Levoit LV-H132up to 129 sq. ft.
Smartmi P1up to 320 sq. ft.

Filtration Technology

The filter is the most important part of every air purifier. All airborne pollution, dust, pollen, pet dander, hair, and even mold spores are removed with a filter. 

GermGuardian AC4825 - Filters
All in one filter is simple to replace and, at the same time, a perfect solution to remove airborne particles from the air.
Check Filter Price On Amazon

The filter is delicate and needs to stay dry for maximum performance. Because of that, never use an air purifier in areas with high moisture. The filter is not reusable, which means you should never wash it or clean it. These actions may damage the filter, and you can have even more pollution at home than before.

Essential oils on the filter are big no. Oils can destroy filters and even damage the air purifier.

True HEPA Filter

GermGuardian AC4825 has four layers of filtration. The most significant layer of air filtration is a True HEPA filter, which stands for High-Efficiency Particulate Air. It destroys up to 99.97% of harmful germs, dust, pollen, pet dander and hair, mold spores, and other allergens as small as 0.3 microns from the air. 

GermGuardian AC4825 - True HEPA Filter
The GermGuardian AC4825 True HEPA filter. Photo: / Milan Antonic

We keep the True HEPA filter at top performance by using pre-filter and regular filter replacements. You will notice a red light blinking on the top of the AC4825 air purifier when it’s time to change the filter. If used properly, the filter needs to be replaced every six months.

Pre-filter + Charcoal

GermGuardian is specific because the filtration system includes two additional air filtration layers, a pre-filter, and a charcoal filter.

The pre-filter + charcoal layer of filtration is significant for catching larger particles like pet hair, and it increases the lifespan of the HEPA filter. Though AC4825 has two extra layers of air filtration, a combination of pre-filter and charcoal is not the happiest combination because this means that there is not much carbon to remove all the bad smells in the room. However, charcoal pre-filter will still be useful for removing odors at a decent time. It would be much better if, instead of a charcoal filter, a carbon pellet is used.

GermGuardian AC4825 - Pre-filter and Charcoal Filter Combination
The GermGuardian AC4825 pre-filter and charcoal filter combination. Photo: / Milan Antonic

Nevertheless, pre-filtering removes larger particles, dust, and some allergens. The charcoal filter prevents excessive accumulation of odor but also reduces the growth of bacteria, germs, and mold. Hence, your GermGuardian AC4825 will get rid of all these impurities from your home and prevent you from inhaling them.


The latest stage of filtration is the UV-C light. UV-C light, usually named Ultraviolet Germicidal irradiation, is proven to be extremely effective at killing germs, mold spores, and even some viruses. This advanced technology is part of the air purifier and can be turned on or off at any time. UV-C light is not the only technology that cleans the air in the GermGuardian air purifier; this popular air purifier also uses a pre-filter, HEPA filter, and activated carbon filter.

How to replace the GermGuardian AC4825 filter?

Step 1

Turn off the air purifier, make sure the power cable is also unplug. After that, open the rear cover by pressing the lock and release button.

GermGuardian AC4825 - process of replacing filter - Opening the rear cover by pressing the lock and releasing the button.

Step 2

Remove the old filter from the air purifier.

GermGuardian AC4825 - process of replacing filter - Removing an old filter.

Step 3

Put the new filter into the unit. Check the arrow on the filter to place it correctly inside.

GermGuardian AC4825 - process of replacing filter - placing a new filter into the unit.

Step 4

Put the cover back and seal it.

GermGuardian AC4825 - process of replacing filter - Closing the cover back.

Step 5

Lastly, press and hold the UV Control Button for 5 seconds to reset the Filter Change Indicator.

GermGuardian AC4825 - process of replacing filter - Pressing and holding the UV Control Button.
The device will not start if the back cover is not closed correctly. This security feature is great and will prevent UV-C light exposure.

UV-C Bulb

UV-C light is one of the best ways to kill dangerous microorganisms. Many manufacturers started to use UV-C light in their air purifiers to provide even greater performance.

GermGuardian AC4825 - UV-C Light Bulb

UV-C light is safe to use in certified air purifiers.

Check Price On Amazon

The GermGuardian AC4825 UV-C bulb position is not the best. It would be much better if it were placed somewhere in the middle of the device and not on top. UV-C light technology works with Titanium Dioxide. Titanium Dioxide is activated by UV-C light and, in combination, kills germs but also removes odor molecules, smoke, cooking odor, and even pet odors.

When the UV-C light is on, you will see the blue light on the front panel. UV-C light is safely contained inside the air purifier, and using it is perfectly safe.

UV-C bulbs need to be replaced every 10 to 12 months.

How to replace UV-C bulbs?

Step 1

Remove the back cover, but make sure the device is unplugged. Immediately after, remove the filter from the air purifier.

GermGuardian AC4825 - process of changing UV-C Bulb - removing the back cover and a filter from the air purifier.

Step 2

Remove UV-C metal shield with Phillips screwdriver.

GermGuardian AC4825 - process of changing UV-C Bulb - removing UV-C metal shield with Phillips screwdriver.

Step 3

Use the clean cloth on the UV-C bulb and remove it out from the unit.

GermGuardian AC4825 - process of changing UV-C Bulb - removing UV-C bulb from the unit by using a clean cloth

Step 4

The UV-C Bulb is reinstalled by pushing it horizontally back into the holes at the unit’s top.

GermGuardian AC4825 - process of changing UV-C Bulb - Reinstalling the UV-C Bulb by pushing it horizontally back into the holes at the unit’s top.

Step 5

Press and hold the UV Control Button for 5 seconds to reset the UV Bulb Change Indicator.

GermGuardian AC4825 - process of changing UV-C Bulb - Pressing and holding the UV Control Button after changing the UV Bulb.

Noise Test

I have tested this device in various situations and different fan speeds. What I like about AC4825 is the difference in noise at different speeds. Some models have an extremely loud third speed, but not GermGuardian. Still, in general, noise could be a little bit lower.

At the first speed, the device makes 46.7 dBA; at the second speed, it makes 50.5 dBA; and at the third speed, this air purifier makes only 54.2 dBA.

It is clear that GermGuardian AC4825 needs sleep mode, which could reduce noise at a lower speed even more. As always, I used a measuring tool that uses the dBa scale, and my results may be different from the official ones. Check out the table below for more details about the noise.

Speed Value (dBA)
Speed 1 46.7 dBA
Speed 2 50.5 dBA
Speed 3 54.2 dBA

Performance Tests

I tested the GermGuardian AC4825 air purifier in different rooms. Only the most significant tests will be included in this review. Overall, AC4825 did a good job. I also tested it with UV-C light and without it.

GermGuardian AC4825 - air quality measurement using a Temptop device.
I measured the GermGuardian AC4825 performance with the Temtop laser particle meter. Photo: / Milan Antonic

The Temtop pollution measuring tool did not find a significant difference in these two tests. I must say I did these tests in real-life situations, and I did not do any tests in the laboratory.

320 sq. ft. Room Test

I tested AC4825 in a 320 sq. ft. large room that is almost two times larger than the recommended one, and the test device did a good job with excellent results. In only one hour of work, AQI dropped from 80 to 8 and improved air quality by 90%.

# Starting Baseline After 60min
PM 2.5 59.4 6.1
PM 10 83.2 8.6
Particles 86210 8972
AQI 80 8

320 sq. ft. Room With UV-C Turned On

In the same room size of 320 sq. ft., but now with UV-C light on, results were not significantly different. AQI drops from 85 to 8, which is 91%. I can say that UV-C light gives an additional 1% boost, which is not that much after all.

# Starting Baseline After 60min
PM 2.5 63.4 6.1
PM 10 88.8 8.5
Particles 92029 8889
AQI 85 8

194 sq. ft. Room Test

A room of 194 sq. ft, which is almost the perfect size, but still a little bit larger than the recommended one. Again, there is not much difference between the tests. In 60 minutes, AC4825 managed to drop AQI from 85 to 7, which is 92%. Again, an excellent job.

# Starting Baseline After 60min
PM 2.5 63.6 5.4
PM 10 89.1 7.5
Particles 92363 7837
AQI 85 7

However, if you need a much stronger device that is meant for larger rooms, check out Winix C535 or Levoit Vital 200S. These two devices have almost two times more power than AC4825.

Operating Costs

AC4825 is powered by a 50W motor that pulls 55W when at full speed and with the UV-C light turned on. These numbers are not high, and you won’t see any significant charges on your electricity bill. In whole month work, 24h every day, this device will cost you only 3.8$ if we consider that the US’s electricity price is 0.12$ per kWh.

GermGuardian AC4825 - Motor Performance
The GermGuardian AC4825 was disassembled and placed on the desk. Photo: / Milan Antonic

When on standby, the device will not use any power. With UV-C light, energy consumption is higher but not significant. A much higher operating cost is filter replacement, which needs to be replaced every six months.

The GermGuardian is an Energy-Star-certified device, but if 55W is too much for you, then take a look at Blueair 411, which uses only 10W of power.

Speed Power Usage (W)
Stand-by 0W
Speed 1 30.8W – 35.1W*
Speed 2 34.8W – 38.6W*
Speed 3 39.0W – 43.1W*

*This was power usage with the UV-C bulb turned on.

FAQ About GermGuardian AC4825

Is the GermGuardian AC4825 safe? 

I have had this GermGuardian model for more than 7 months, and according to all the tests I did, it’s an absolutely safe device for usage.

Can it be caught on fire?

I contacted GermGuardian support to check if there was something in this device that could have caused the fire. But I didn’t get any response according to my question. Anyway, I don’t have any problems with the AC4825 air purifier, and there are more people who have had a positive experience using this device. However, to make sure that there will be no problems while you are not at home, I suggest turning off the GermGuardian AC4825 air purifier when you leave the house.

Is it safe to leave the air purifier on all day?

Yes, it’s safe to leave the GermGuardian AC4825 turned on all day. But, when you are going out, turn it off.

Is GermGuardian ozone-free?

All of the GermGuardian air purifiers comply with UL safety standards 507 and 867. On the other hand, the company must comply with the California Air Resource Board, which closely regulates air purifiers. The AC4825 had a maximum ozone output of .001 PPM at low speeds and was not detectable at other fan speeds.

Are GermGuardian filters washable?

No, the filters on GermGuardian AC4825 are not washable.

How often do you change the filter on an air purifier?

The GermGuardian AC4825 air purifier’s filter should be changed approximately every 6 months.

How often does UV-C light change?

You should replace the UV-C light every 12 months.

4 responses to “GermGuardian AC4825 Review – Top-Selling Air Purifier”

  1. Phin

    Thanks for the review! We’ve had four working since 2018 and they’ve all held up well to daily, 24-7 use. The medium and high speeds are a bit loud so they’re usually on low. It would be nice to be able to test the air quality, but we haven’t looked into air quality monitors yet. I might have missed it, but what speed did you administer the tests, and do you happen to know how clean you can get the air on different speeds?

    • Milan Antonic

      Hi, thanks for sharing your experience.

      I have used it on the max speed when testing and haven’t performed similar tests on other fan speeds.

  2. Kathryn Thomas

    I purchased the smaller plug in unit. I was very impressed and ordered 2 more. However, last night, I luckily went downstairs to get a glass of water and heard a strange noise which I tracked to the germ guardian plugged into the kitchen outlet. It was smoking a starting to catch on fire!!! I believe these smaller units have some type of malfunction which had I not uncharacteristicly gone downstairs, would have been in full flames. Please investigate these units.

    • Milan Antonic

      That’s strange, as I haven’t noticed anything similar on the GermGuardian air purifiers I have tested and used so far (this one and the GermGuardian AC4200W). I suggest contacting Guardian Technologies directly, explaining the situation, and asking if there is any known glitch with the model you are talking about. Also, till now, I haven’t gotten any comments complaining about malfunctions such as the one you have described.

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