GermGuardian AC4100 Air Purifier Review

Up until now, we have reviewed only larger floor standing air purifiers at With today’s air purifier review, we decided to look around for small table top or portable air purifiers. The GermGuardian AC4100 air purifier is popular unit for very small rooms, dorm rooms, desktops, at work, and in cubicles.
One novel use for the a table top air purifier is placing it next to a 3D printer for the smells it generates when printing. You see, 3D printers heat up plastic filaments to melting temperatures, and some of the plastics create an unpleasant odor.

Filter Type or Filtering Process

The GermGuardian AC4100 air purifier uses three stages for air purification: 1) a charcoal pre-filter for larger particles and odor reduction 2) a “near HEPA” filter with 99% filtration and 3) a UV-C (ultraviolet in the “C” band) combined with a titanium dioxide (TiO2) screen to kill germs. We will get more into the details about this below.
The air path is as follows: Air enters through the back, then through the prefilter and the “near HEPA” filter, both of which are at the back of the machine, then is sanitized using the UV-C lamp and TiO2 screen, then exits through the front, at a 45 degree angle – so it’s not straight at you. This is especially nice in the winter, or during cooler days, as you don’t want a constant breeze aimed at you, especially if you use this air purifier on your desk while working.
You might be wondering about the “near HEPA” or 99% filtration of the GermGuardian AC4100 air purifier. 99% filtration means it captures air particles down to 0.7 microns in size, whereas true HEPA at 99.97% filtration means capturing particles down to 0.3 microns. This means dust and mold are captured, but smaller particles such as bacteria (0.4 microns) that a true HEPA filter would catch are not captured by this filter. The difference between 99% and 99.97% may not seem like much, but consider this: It is the difference between letting 3 out of 10,000 particles through, which means blocking 9,997 or 99.97% of them with a true HEPA filter and letting 100 out of 10,000 through only blocking 9,900 or 99% of them.
This is why some marketing departments give names like “near HEPA” or “HEPA like” or “HEPA type” to 99% filters. They are not legally allowed to call them HEPA filters, unless the filter can meet or exceed the 99.97% standard. Incidentally, finding a desktop true HEPA air purifier is fairly difficult as not many companies make them. However, the GermGuardian AC4020 air purifier has True HEPA has 99.97% filtration, though it does have an inferior UV-C system (more on this later).
Now with the GermGuardian AC4100 air purifier, you might be wondering what good is it, or what use could it have, since it’s not true HEPA? We think it still has a use, if combined with a true HEPA air purifier. We will explain more a little later on in this review.
The third and final stage of air purification by the GermGuardian AC4100 air purifier is a glass tube fluorescent type UV-C lamp combined with a with titanium dioxide (TiO2) coated screen to kill airborne bacteria, viruses, germs and mold spores.
The UV-C Lamp lasts about 1 year and needs annual replacement. Even if it does not burn out, it’s effectiveness is reduced after a year of on-time. This is because the mercury in the vapor deposits itself on the inside of the tube wall, dimming it. Once nice thing about UV-C technology is that ozone, a harmful gas, is not created.
A slightly more expensive unit (about $10), the GermGuardian AC4020 air purifier comes with a true HEPA filter, which is better and more effective at removing germs from the air (the HEPA filter alone is good for filtering germs). The AC4020 claims to have LED based UV-C lamp, which lasts longer. However, during our research, we discovered that LED Based UV technology is not yet mature enough for the LED in the AC4020 to be truly effective. UV-C type LEDs that are actually capable of the claims Guardian Technologies make about the AC4020 cost about 2 times the price of the AC4020. The LED that the AC4020 has in it is the wrong wavelength. You are better off with the AC4100 with the older (but proven) mercury vapor fluorescent lamp if you want to kill germs with UV-C technology. On the flip side, the AC4020 has a HEPA filter, which is better at removing germs all by itself.
The AC4100 and AC4020 use differently sized filter elements, so you cannot use the true HEPA filter of the AC4020 in the AC4100 to try to get the best of both worlds.
Earlier, we mentioned we still think the AC4100 is useful, even if it does not have true HEPA filtration. We think it would make a great complementary air purifier to use combined with a true HEPA floor unit.


The GermGuardian AC4100 air purifier is a small table top unit, and as such, one cannot expect it to filter a large room. You need a much larger floor unit for large rooms. For very small rooms, or for filtering the air immediately near you (such as your desk or cubicle) it works extremely well.


GermGuardian AC4100 air purifier has a Clean Air Delivery Rate or CADR is 64. This means it’s rated for up to a 100 sq ft room. CADR is a number rating up to 450 maximum, assigned by the Association of Home Appliance Manufacturers (AHAM)


The GermGuardian AC4100 air purifier requires a replacement pre-filter and near HEPA filter (99%) sold together FLT4100 “Filter-E”. About $20 These need replacement every 6-8 months. You must use genuine Guardian Technologies brand filter to maintain warranty and performance. The LB4100 replacement UV Bulb about $15. This lamp is a fluorescent, mercury vapor based lamp. It is environmentally hazardous, and toxic if you break the lamp, such as during lamp replacement, so be careful not to break the glass tube. It must be replaced yearly.

Energy Consumption

We have data for only the highest fan setting on the : 67 watts
The GermGuardian AC4100 air purifier has no Energy Star Rating. Our research indicates no tabletop air purifiers have Energy Star Ratings. Please note that most floor models of air purifiers usually do.

Annual and Monthly Running Costs

We calculated the energy consumption of the GermGuardian AC4100. We also calculated energy costs plus the costs of filters, based on changing the filters on the recommended schedule.

Energy Consumption - GermGuardian AC4100 Air Purifier Review

1) Energy costs = 12 cents/kilowatt (average USA price)
Data (C) 2016

Energy and Filter Change (Total) Costs - GermGuardian AC4100 Air Purifier Review

1) Energy costs = 12 cents/kilowatt (average USA price)
2) Activated Carbon Pre-filter changed every 3 months
3) HEPA filter changed annually
Data (C) 2016


The GermGuardian AC4100 air purifier has a three position rotary knob controls fan speed, low, medium, and high. There is an on/off push button to turn on or off the UV-C lamp. There is a also a rotary indicator on the back that you set manually, to remind you when it is time to change the filter.

Other features

Small size, resembles a bookshelf stereo speaker.
UV-C lamp, combined with TiO2 technology to kill germs.
Date wheel you set manually to remind yourself when to change the filter.
Can be set up to run horizontally (on its side) or vertically, as shown in the photos. Comes with 4 felt stick-on pads that are the feet. You can stick them on yourself, depending on which way you want to setup the unit.


11 inches high x 6.5 inches wide x 7.5 inches deep. It weighs 4.9 lbs and has a 6 ft power cord.


Can be placed on its side.
3 stage filtration: Carbon, HEPA and UV-C/TiO2
No bright lights, so easier to use in a dark room when sleeping


Not true-HEPA – 99% filtration or “almost HEPA”.
Can be a bit loud, especially on higher settings. The larger, more expensive, floor standing AC4825 from the same manufacturer is a lot quieter.
Filters are 1/3 the cost of the unit.

Consumer Ratings

GermGuardian AC4100 air purifier is rated very highly by consumers. It is really good at eliminating odors in rooms with cat litter box. It works very well in young boys’ room. It also works great at eliminating odors in bathrooms that do not have a ventilation fan. It is recommended that it be run 24/7. it has no external bright lights on the unit, so it is ideal for sleeping. It resembles high end audio speaker. Noise is present but is also minimal. Please note that noise is a matter of opinion. Some say its silent. Some say it resembles a white noise generator and some people found it helpful to sleeping.


1 year limited


Under $60 at the time of this writing. Click for current price.

Leave a Reply

Your email address will not be published.