Frequently Asked Questions


What is a Corsi-Rosenthal (CR) Cube?

It's a simple air cleaner pairing powerful fans with relatively high flow MERV13/14 furnace filters that catch virii & pathogens with 72-90% efficiency per pass. The CDC discusses them in its new 5 Air Change per Hour minimum ventilation guidelines for indoor spaces:

Some great articles about them:

How do Clean Air Kits compare with DIY box fan CR cubes?

Both use MERV13 or MERV14 furnace filters that capture at least 77% or 88%, respectively of virus (and PM2.5) per pass. Some experiments suggest even better clearance at low CR box air speeds. High fan flows hasten multiple passes to drop contaminant concentrations in the room faster than tiny flow 99.97% per pass HEPAs.

Depending on fan model and filter brand, Corsi Rosenthal cubes with 4 filters on low speed have a clean air delivery rate (CADR) in 300-450 CADR range using ~65W @52-55 dB. Our Healthy Glow, Luggable XL, and Tower of Power cover this range using 10-16W power @42-44 dB. CR box fan cubes on high speed can reach 700-800 CADR but make too much noise for conversational situations.

How can Clean Air Kits be safer than HEPAs of comparable maximum capacity (clean air delivery rate)?

What matters for room cleaning is the total rate of contaminant particle capture. We have never encountered a HEPA running in the wild at it's Max, often called "turbo" setting. People may max them briefly during an illness or smoke scare, but instinctively turn them down to reasonably "quiet" once any perceived emergency has passed. The "quiet" speeds tend to clean air < 1/2 as fast as the HEPA's max rated capacity, though intermediate speed specs are hard to find. (This does not apply to the SmartAir Blast exceptionally quiet large HEPAs). A Clean Air Kit runs quietly at one speed ... it's full CADR capacity, providing a consistently high level of protection.

The HEPA industry has a habit of advertising the clean air delivery rate of their highest speed (usually loud 50-65 dB) paired with their lowest speed or 'sleep' mode noise < 30 dB. This makes it nearly impossible for consumers to pick the right size & number of HEPA for a space under realistic sustainable ~35-45 dB noise levels. CleanAirKits only have one quiet speed so we don't play this misleading marketing game!

How were your CADR (Clean Air Delivery Rates) measured?

One sample each of Luggable 5-Arctic, Luggable 5-SickleFlow, Luggable XL and Exhalarons were tested by Intertek for AHAM AC-1 CADR, AC-2 Noise & Power:

  • Luggable 5-Arctic: DUST 189 cfm
  • Luggable 5-SickleFlow: SMOKE 170, DUST 218, POLLEN 236 cfm
  • Luggable XL: SMOKE 259, DUST 323, POLLEN 370 cfm
  • Exhalaron: DUST 70 cfm
  • Exhalaron Ultra: SMOKE 79, DUST 88, POLLEN 104.4 cfm

ASHRAE 241 specifies reducing these to a single infectious aerosol CADR via the formula:
VirusCADR = .3*SMOKE + .3*DUST + .4*POLLEN

For our samples so far this average comes out the same as the DUST measurement. Where we have SMOKE, DUST, & POLLEN results we display the VirusCADR, where we have DUST only we display that. Studies of exhaled viral aerosols also show a particulate distribution closest to AHAM DUST.

Full AHAM Verified requires testing 3 samples with Smoke, Dust & Pollen costing ~$5k per model. We have too many models to afford that yet on all. But for optimal fan to filter-area ratios (1 SickleFlow per 1 sq ft of Filtrete 1900), we can extrapolate amongst related models.

The official Intertek test results are in these files:

Luggable 5-Arctic DUST CADR

Luggable 5-Arctic Sound Power

Luggable 5-SickleFlow Smoke/Dust/Pollen CADR

Luggable 5-SickleFlow Sound Power

Luggable XL Smoke/Dust/Pollen CADR

Luggable XL Sound Power

7-Arctic Luggable/Healthy Glow DUST CADR

7-Arctic Luggable/Healthy Glow Sound Power

Our early development procedures and test results have been publicly shared and documented in this blog:

and this Twitter thread compilation:

Rob's elaborate characterization process mimics AHAM laboratory particle detection procedures but uses nebulized salt. He has calibrated his setup against CADR measurements of commercial purifiers by independent laboratories and found agreement, though the results seem to skew closer to AHAM POLLEN than AHAM DUST.

Our stated capacities are also consistent with simpler estimates adding the raw CFM airflow specifications of the bundled fans and multiplying by MERV13's measured 77% viral aerosol filtration efficiency.

Have CleanAirKits been UL & FCC tested and certified?

Our assembled Exhalaron, Luggable, and EndTable lines with CoolerMaster fans have been FCC & UL507 certified for US and Canada by Nemko Labs. Fully assembled units get FCC & UL507 electrical safety marks on their sticker.

Because factory inspection of each unit is required in the UL507 process, unassembled STEM kits from the Luggable or EndTable line do not get the UL507 sticker. However, these STEM Kits contain the same UL-registered fans and power supply (and assembly procedures) as factory assembled units.

Because the popular Arctic P12 and P14 fans used in the Bedroom Luggable and Tower of Power are not UL-registered components, those models cannot get the UL507 sticker either, whether pre- assembled or not.

Can Clean Air Kits run off a portable battery?

Yes. You just need this USB C PD 12V DC barrel adapter (also available in our shop) with one of these pre-tested PowerBanks. The first two have male pigtails and < 5.9" tall to fit nicely in Exhalaron:

VRURC T2046 20000mAh (12 hours)

Charmast C2046S 20000 mAh (12 hours)

These don't have male USBC pigtail or perfect fit for Exhalaron, but do output 12V with our USBC to DC Barrel adapter:

Anker GaNPrime 733 Power Bank 10000 mAh 

Anker 335 Power Bank 20000 mAh, 20W

Anker A1367 Power Bank 20000 mAh, 15W

(Durations shown for Exhalaron or 5-fan Luggables). With the USB PD cable you can even run them off your laptop! Try to pick these specific cables and power banks because we've tried many others that will only deliver 5V to the fans leaving them pretty weak. Also note the LianLi Healthy Glow needs both 5V & 12V, so would need a different adapter setup.

Which models have handles?

We can do way better with the Luggable than this dolly-strapped CR Box!

Every Luggable comes with a handle. Handles are optional on Tower of Power.

Which models have mesh filter guards available?

Mesh Filter Guards are now available for the Luggable and Healthy Glow models to protect filters from prying little fingers and claws. Tens of thousands of CR Boxes have been deployed in homes and classrooms with filters exposed this way. The CDC estimates that only 1 of 10,000 COVID transmission is thru fomites (surface contact) compared to airborne transmission, so removing COVID from the air should be priority. That said, the filters do accumulate dirt & (mostly inert) pathogens, so people & kids should avoid touching the filters. Wear rubber gloves & an n95 respirator during filter change & disposal.

Is there a fan speed control?

We don't include one because our kits are so quiet and energy efficient already, and if intention is to maximize cleaning of respiratory pathogens, they should stay on full when people are around. If you really want, you can retrofit a LianLi HealthyGlow with this CoolMoon fan controller that includes a remote with speed control buttons:

Is there a timer or motion sensor feature?

Not built in. We recommend plugging through a timer, motion sensor or light sensor so filters run at times of day people are expected to be around. We offer a couple of these as accessories in our online store. But our purifiers are so energy efficient, that they won't use much energy overnight either.

Can I rearrange the rainbow fans e.g. all on one side?

Yes. Fans are attached with pushpins. First slide out a filter. Then pull on fans with some force from the inside and they will detach. Re-order fans as you like. You can even change their direction to face out and blow in (though they may accumulate dust faster). Or put them on outside of box (though wiring may lessen seal).

To avoid tangling the wires, wires may be detached from the hub and reattached in a less tangled order.

I heard that cleaning and sanitizing the air uses too much energy. Aren't you worried about global warming?

We are. However, thanks to the amazing efficiency of our CPU fans paired w/ MERV13, our purifiers use several times less power than most HEPAs. In fact our Tower of Power can add 3 air changes per hour to a large classroom using only 12W of power, about the same as an LED light bulb. Remember LED light bulbs are 5x more efficient than the incandescent light bulbs they replaced too. Energy efficient building retrofits are a vital tool against CO2 emissions. We consider this technology to be as positive for building efficiency as LED lighting.

Mechanical timer plugs and motion-activated plug accessories are available in our online store to focus filtration on times that rooms are occupied and extend the life of your fans and filters. For a bedroom, you can set the mechanical timer on nights and mornings. For family areas, set the mechanical areas for daytime and evenings.

Does a Clean Air Kit create mix a room as well as a HEPA or CR Box fan? Does it make a cold breeze during the winter?

This depends a bit on which fans you choose and whether they're pointing up or to the side.

The SickleFlow and Lian Li fans have more focused flow that can be felt a couple meters away. The 150fpm throw for these fans is 4 ft, about the same as a CR Box fan on low. This helps them circulate larger rooms. Corsi & Rosenthal have done experiments verifying that one CR Box fan effectively removes particulates from a whole classroom.

We did our own experiment in a 600 sq ft open living area here, and the XXL side fans helped it circulate the room more evenly than a large HEPA with very strong upward throw!

The Arctic p12 fans push air out in more of a cone pattern than a focused beam, so don't throw as far and don't make much noticeable breeze. This is OK for smaller rooms that need less mixing, or if you dislike chilly breeze.

A slow ceiling fan can also help with silent, thorough room mixing.

Do you make a metal CR Box enclosure like a PC case?

Not yet. Our enclosures are highly portable, with lightweight wood or plastic materials that blend warmly into living areas.


Will CleanAirKits keep my family safe during our unmasked gathering?

With COVID's unprecedented transmissibility, no single mitigation is foolproof: not vaccines, not masks, not nasal sprays, not RAT testing, not air cleaning. Each has a substantial failure rate in certain situations. However, when these measures are combined in multiple layers of protection that multiplicatively reduce risk, high safety can be achieved. For instance, doctors wearing well-fitted N95s plus eye protection working daily in COVID infectious wards with 12+ ACH air filtering can avoid infection for months, and are most at risk from their kids bringing COVID home from school.

Try to setup multiple layers of protection for gatherings, like:

1) 12 ACH indoor air filtration or held outside, and guests keep some distance so exhalations have some space to dissipate toward cleaners or breeze

2) each guest submits same-day negative RAT or wears n95 mask

Are masks still needed if using a Clean Air Kit?

N95 Masks and bulk air purifiers are really complementary, forming multiple layers of protection that multiply together to dramatically lower transmission risk. Rapid air cleaning reduces the "far field" risk from spreaders across the room that could eventually pervade the room with virus and cause a super spreading event. Statistically, 12 ACH is similar to an n95 in the far field, reducing viral concentrations 95% between people several meters apart. However, just like outside, there's still substantial "near field" transmission risk talking face to face with an unmasked infected person in close proximity, especially when the infected person is closer to you than the purifier. The purifier may not get a chance to clean before you receive an infectious dose when someone is breathing directly on you. For pretty foolproof protection, use two-way masking & purifiers, like doctors do in infectious wards. Also, air cleaning is crucial for any indoor group dining, where people necessarily won't be wearing masks.

Is it more dangerous being close to the filter and flowing air?

We'll let the estimable HVAC engineering expert Joey Fox answer this one:

Is it safe to run so many fans in a box? What if they become overloaded?

With factory-assembled and fan-bundled kits we provide a UL-listed 12V 2A AC wall plug adapter. Only 12V from standard DC barrel plug goes into the box. Each fan only uses about 1 Watt. All fans connect internally via standard 4-pin hubs and splitters manufactured for connecting PC fans, without any custom hand-soldered connections. We use static pressure fans designed to operate under high resistance/load. These fans sense when they are blocked by a foreign object and stop automatically. They will spin back up a few seconds after the blocking object is removed. Compare our rigs to the millions of custom-built gaming PCs containing multiple rgb cooling fans scattered across the USA.

This seems too simple to be effective. And it's lacking the fancy wireless digital readouts of a high end HEPA.

Does your HVAC system need fancy digital readouts and ionizers to clean the air? No. Just a powerful metal fan, ducts, duct tape and the quality filter you slide in. Dean Corsi and Rosenthal and SmartAir have repeated this Occam's razor of indoor air quality over and over again. Strong quiet fans and quality MERV13 or higher grade filters make good air quality. Most extra purifier features are marketing gimmicks. The marketing strategy around dense HEPA filters for ideal 99.97% single-pass removal boxed the industry into engineering noisy & inefficient room purifiers. It's mainly important for sterile compartments and personal purifiers that may point at your face, so we do use HEPA for the Exhalaron. For room cleaning, each thimbleful of 99.97% HEPA-cleaned output air quickly remixes with room contaminated air. Wouldn't you rather mix a cubic foot of 90% clean air back into the room?

Are the fan guards really necessary?

Everybody (especially kids) likes to stick their fingers in the fans and play. Fans of this power can't leave much more than a scratch, but the fan blades are thin. They can easily break if something falls in. Therefore we recommend keeping the fan grills, especially where kids or pets are around, to prolong the life of the product.

I heard that cleaning and sanitizing the air uses too much energy. Aren't you worried about global warming?

We are. However, thanks to the amazing efficiency of our CPU fans paired w/ MERV13, our purifiers use several times less power than most HEPAs. In fact our Tower of Power can add 3 air changes per hour to a large classroom using only 12W of power, about the same as an LED light bulb. Remember LED light bulbs are 5x more efficient than the incandescent light bulbs they replaced too. Energy efficient building retrofits are a vital tool against CO2 emissions. We consider this technology to be as positive for building efficiency as LED lighting.

Mechanical timer plugs and motion-activated plug accessories are available in our online store to focus filtration on times that rooms are occupied and extend the life of your fans and filters. For a bedroom, you can set the mechanical timer on nights and mornings. For family areas, set the mechanical areas for daytime and evenings.

STEM Kit Assembly

How do the STEM kits assemble?

Early versions of the STEM kits hung together with double-sided tape making filter replacement a bit of a chore. We've transitioned to slide- or screw-together kits for faster assembly and easier filter changes.

The assembly process takes 20-30 minutes.

  1. Attach grills to panels first with push pins. Place panel on table grill side down. Orient all fans so their wiring exits on the same side. The writing on the back of the fans needs to face the grills and out of the box, unless you want fans blowing in and accumulating dirt quickly. Once properly oriented, firmly push fans all the way onto the push pins.
  2. One side panel should have a grommet hole for the power cord. Make sure that goes toward the bottom of the box. Screw top and bottom plates into side plates (or vice versa for End Table).
  3. Connect all the fan cables to the 5-way hub (Luggable) or two 3-way splitters (End Table).
  4. Tie the light bungee cord between opposite side panel adhesive hooks (Luggable 5-fan), or between opposing side fan screw holes (End Table 6-fan).
  5. Secure the 5-way hub or 3-way splitters to the center cord with a twist tie or zip tie.
  6. Plug the hub/splitter connectors into the 4-pin ends of the DC barrel adapter cable, or directly to your AC power adapter if it has a 4-pin fan connector
  7. Connect the AC power adapter and test that all fans run without obstructions or cable interference.
  8. Remove power and prepare for closing the box by slipping the filters into the sides. Gently pry up edges until unwrapped filters slip in, with airflow arrows pointing into the box.
How much work is kit assembly?

Assembly takes 20-30 minutes

1. Attach the fans and grills to fan plates with either the push pins or screws provided. All fans must point the same way, usually with fronts facing into the box so fans push air out of the box and blades stay cleaner. (5 minutes)

2. Connect fan wires thru 5-way or 3-way hubs/splitters. (2 minutes)

3. Before completely closing up the box, tie tensioner cords between opposite side hooks or fan holes, and secure and tie wires to tensioner cords so they can't drift into the fans. (3 minutes)

4. Connect final DC barrel adapter to fan connector hub(s) and attach strain relief grommet. (3 minutes)

5. Close up the box checking for any large gaps and sealing. (Tiny gaps will not significantly affect performance)

Which other CPU/argb fans will work in this kit?

Many CPU fans are too weak to push air through MERV13, while some of the strongest can be too loud. Avoid 'case' or 'flow' fans as they don't hold enough static pressure to push through the filter resistance. For best results, find "static pressure" fans specced at least 1.6 mmH20, preferably > 2.0 mmH20, and > 50 CFM. The higher the static pressure, the better filter air flow will hold up as the filter loads with contaminants.

The following RGB/aRGB fans should produce roughly similar filter performance as Arctic P12s:

These fancier argb kits require both 12V and 5V and generally have twice as as many wires to deal with as the 12V-only fans we bundle. You will need to get a 12V & 5V 2A-5A AC adapter plus Molex to SATA adapter as described in previous question.

Which way should filters point?

In the normal setup with fans blowing out of the box, the filter arrows should face the inside of the box. The arrows on filter box ensure the wire mesh supports filter media under strong furnace fans. Frankly, it doesn't matter much for slow airflow from CPU fans.

Which way should fans point?

So long as they're all oriented to blow the same way, the box will work. They can also be mounted either on the inside or outside of the box, depending on visual preference. Usually we mount the fan backside facing outward so the fans suck through the filters and blow out, keeping the fans cleanest. With fan fronts facing out, CPU fans will blow into the box and accumulate dust faster, but filter dirt will accumulate more on inside than outside of the box.

Does the box have to be sealed perfectly?

CleanAirKits boxes operate at fairly low pressure so small gaps (< 1mm) or holes shouldn't affect performance too much. There are small gaps elsewhere like between the fan blade tips and fan housing that sometimes help not hurt performance.


How easy is it to replace filters?

WARNING: Filters do accumulate dirt & (mostly dead) pathogens, so we recommended wearing rubber gloves & an n95 respirator during filter change & disposal.

Simply grab the filter by its cardboard frame and pull it out. Then slide in the replacement. Our YouTube channel has a video showing this procedure. Elastic tensioners inside the box maintain a slightly snug fit all around.

For legacy STEM kits with filters double-side taped to panels, peel back the gaffer tape along a bottom edge first, and then begin pulling panels apart from the taped filter edges. Reapply double-sided tape as necessary and refold panels around the new filters.

What replacement filters can I use?

Our fan flows are optimized for 3M Filtrete 1" MPR 1900 or 2200 that also meet the MERV13 spec.

Recent experiments show that Filtrete MPR1085, MPR1500 (a MERV12), & MPR2500 (a MERV14) achieve DUST & POLLEN CADRs within +-5% of MPR1900 in SickleFlow Luggable kits. Likewise for Arctic P12 Luggable, except it was 10% weaker with MPR2500. Our test equipment could not measure the smallest particles in SMOKE CADR, but we have no reason to believe they strongly deviate. Feel free to choose the best deals within the Filtrete MPR1085-2500 range. e.g. MPR1085 often cost only half as much as MPR1900.

To maximize performance, use only genuine Filtrete replacements. Filtrete MPR 1085-2500 are widely available at Amazon, Lowes, Costco, Digi-Key, Walmart, etc.

Most other MERV13 furnace filter brands require a 2" thick filter to achieve the same high flows as the micro-pleated Filtrete 1". If you put a 2" thick MERV13 filter in our boxes, 1" of that will stick out, but performance should be close to the Filtrete 1"

How long will filters last?

Depending on how well your HVAC system is additionally filtering dust, they should last 6-12 months. Filters may visibly darken after a couple months, but will keep operating at somewhat reduced airflow.

Heavy wildfire smoke or placing next to a fireplace can accelerate aging of the filters and neutralize their electrostatic charge. We recommend replacing all filters after heavy wildfire seasons.

Send us your dirty filter pics for the filter of the month contest, and we just might air your dirty linen!

Why do you use 3M Filtrete brand filters

As many testers have found, Filtrete have the best airflow (least static pressure drop) and clean fastest among MERV13 filters: