Indoor Air Quality at Alexander's Martial Arts


How We Protect Our Members

     This handy graphic from ( explains how to improve air quality in a classroom. Our physical situation is a little different, but the concept and the need to protect our kids is the same.

     Here’s how we’re addressing each:

Windows: Since we don’t have the ability to open a window, we’ve added a Dedicated Outside Air System to the building. Provides 1300 CFM of filtered and conditioned outside air and removes the same amount of stale air from the building.

Air Movement: The HVAC and DOAS fans are running the entire time classes are going on. You can see the ribbons.

Thermostat: Fans ON during classes (merv-13 filters in HVAC).

CO2 Levels: The DOAS has cut the CO2 during our largest classes by 2/3. More oxygen! Better physical and mental function.

HEPA/CR Box: You’ll see HEPA filters in the restrooms and CR Boxes on the training floors.

Additional Measures: Upper room and in-duct UV disinfection.


Recommended Clean Air Deliver Rate (CADR)

In a Gym: 80 cfm per person

Spectating: 50 cfm per person

Dedicated Outside Air System (DOAS)

Our Biggest Investment in Clean Air

Because we cannot simply “open a window”, we’ve invested in a DOAS for the karate school. In this case, it brings in 1300 (two units at 650 each) cubic feet per minute of filtered and conditioned (heated/cooled) air and returns a similar amount of “stale” air to the outside. So it’s like having an open window that dehumidifies and temperature corrects too! This was a huge investment (~$80k) but there really was no other effective way to bring in that volume of temperature and humidity controlled outside air. Below is an exert from a white paper from Fujitsu (as well as a link the the paper).

From White Paper: DOAS are dedicated ventilation systems designed to condition outdoor air during ventilation. Depending upon the application, a DOAS may also have energy recovery capabilities. While an ERV can handle approximately 50 percent of the load to bring outside air to room neutral temperature, the addition of mechanical cooling and heating allows a DOAS to fully condition the incoming outside air. For example, in a humid climate, a DOAS unit could cool 95-degree outside air down to the dew point — which is typically in the 50-to-55- degree range — and then reheat it back to 77 degrees, before introducing it to the building as room neutral ventilation air. 

DOAS are available as packaged equipment or as a split system to support decoupled designs. Packaged equipment accounts for most of the current DOAS market. While cost effective at startup, and simpler to install, packaged equipment does not offer the same design freedom as a split-system DOAS. With split-system DOAS, architects and building owners can separate and strategically arrange VRF outdoor units and DOAS equipment.

Air Movement (and filters) & Thermostat Fan in "ON" Position

     This is another thing you might think is simple, but there’s a little more to it. We’re always trying to be good stewards of the environment while we’re also doing what we can to make the school as safe as possible.

     The first step was to replace all the standard merv-8 filters with merv-13 filters. The higher the merv rating, the more effective at catching small particles. A good merv-13 filter catches about 77% of the particles in the size regime of the covid-19 virus. 

     The next step is to keep the fans on even when the temperature does not call for the heating or cooling. Because commercial hvac systems bring in a certain amount of outside air by design (~10%) this can present a humidity problem for the building and could cause other unintended risks (like mold). Fortunately, the DOAS controls humidity (as does the ac when it kicks on). So the DOAS makes it feasible to run the hvac fans even on “nice days” when we don’t need to adjust the temperature!

     That’s excellent because the hvac moves a lot of air (and since we’re using merv-13 filters) also filters a lot of air. This system moves about 6k cfm of which 600 is fresh air and 5400 is filtered. Estimated CADR > 4000 cfm.

CO2 Levels

     This one came as a bit of a shock because we’d always worked out indoors with no regard to CO2 levels in the air. In fact, we didn’t immediately know how to assess CO2 in the air. In retrospect, we’ve have an intrinsic understanding of CO2 levels since the days of Batman and Robin (or some other super hero from our youth) getting locked in a vault and “running out of oxygen” or at least since grade-school science class taught us that we breath oxygen and expel CO2 and plants do the opposite.

     CO2 levels became a proxy for air freshness (the higher the CO2, the more “human exhaust” you’re breathing) and with asymptomatic infection a real possibility, you don’t know if that exhaust is “sick”. So, people started to use portable CO2 monitors to assess the freshness of air and share that info online (it turns out the monitors are readily available and not too expensive).

     High CO2 levels are linked with a host of issues: drowsiness (think opening your windows on a long trip), JKJKKJH, JKJKJKHK, and of course it indicates how much “exhaust” your breathing. Unfortunately, simple particle filtration will not reduce CO2, but our trusty friend the DOAS flushes the air and replaces it with “fresh” air so it drastically reduces the CO2 and the “exhaust” in the air. 

     Since the addition of the DOAS, our biggest adult class at the end of the day (when CO2 has had it’s best opportunity to build) has seen a reduction in CO2 levels from almost 3500 ppm to around 1100 ppm at the peak with a steep fall off rate and CO2 rates tend to stay below 1000 for other classes! For reference outdoors runs around 400-500 ppm.

More information below on CO2 levels and safety.

HEPA Filters and Corsi-Rosenthal Boxes

     Since we know the particle sizes we’re trying to remove and since we know how to do that (filtration) one of the simplest ways to clean the air is to run it through a filter. There are a couple of considerations here (like in all things). 

     The first consideration is noise level. As nice as it would be to just get some good filters and a “jet engine”, moving that air by mechanical means makes noise and burns energy.

     HEPA filters are a great way to filter the air. They’re 99.??% effective, but because of the density of the filter they limit the amount of air that passes through. They also tend to be pretty expensive (as do the replacement filters). To get the kinds of CADR numbers from the first panel above, you need a lot of HEPA filters.

     Interestingly, during the early days of the pandemic, some guys came up with a make-shift solution using a cheap box fan and good (but not HEPA good) filters. The result is that you can run MUCH more air through these filters and need less motors spinning. Merv-13 filters are about 77% effective at removing virus particles from the air. That means if you run 1000 cfm through a merv-13 filter you produce over 750 cfm of clean air and therefore reduce contaminate load by more than 3/4. 

     Our approach is to use the more compact (and noisy) HEPA filter in the smaller rooms at the school (restrooms) and to deploy a number of CR Boxes on the main floor. We have benchmarked our filters (the ones with the Honewell fans and 20x30x1 merv-13 filters) at 675 cfm CADR. That means 3 on the main floor produce a little over 2000 cfm of clean air.

More on CR Boxes below (they’re great for removing all kinds of small particles)

Upper Room UV

     Specific wavelengths of Ultraviolet light are used in hospital and surgical settings for disinfection. The drawbacks are that the pathogen must be directly exposed to the UV and direct UV exposure can be harmful to people. The solution is to do two things: 1. move the pathogen in front of the UV and 2. direct the UV so people are not directly exposed.

     We’ve installed Aerpathy Zone 360 lights on the ceiling. They employ a fan to circulate air (as well as relying on the other air circulation we have in the room) and they irradiate the top foot or so of the room. The same or similar devices are deployed in major airports, hospitals, and adLADJKal;fjkshajkd;fhjk


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