No, not from us. But our favorite models are being discontinued, so now is the time to buy.
The story: In the first year of the pandemic, several schools we worked with were not going to be able to make the extensive and expensive fresh air ventilation improvements to provide 100% of the needed fresh air. So we did the best we could with existing equipment, made minor modifications, and supplemented this with in-room air purifiers. As you may know, virus in the air can be removed by flushing it out with fresh air, or filtering it out with a HEPA filter—and, most importantly, these can be both happening at the same time. Open your windows AND run your air purifiers. (This is backwards from what we used to do when thinking that the polluted air was outside—now the “polluted” air is inside, so things are reversed.)
We explained air purifiers in our Sept. 30, 2020 report. You can see the whole report at COVID-19 Mechanical Engineering Recommendations (PDF). The last three pages of this report are the HEPA Air Filtration Unit Selection Guide, reprinted below.
Blueair is discontinuing the Classic 205 and Classic 605. They may still be available on the Blueair website, and they are also available from Amazon and other sources, at big discount prices. The 205 is my favorite model—we have dozens of them in schools—and is easy to carry around if you sometimes need it portable. Search for "Blueair Classic 205 Air Purifier”, with the quotes.
Sizing note: You should have a minimum of 15 cfm/person of real fresh air. Beyond that, you can provide additional fresh air and/or purified air. For purified air, I recommend an additional 10 cfm/person as a minimum. (See Improving COVID-19 Safety within Buildings - A Do-It-Yourself Guide for Building Operators (PDF) for more information.) Good luck, and here’s to breathing cleaner air!
HEPA Air Filtration Unit Selection Guide:
The COVID-19 pandemic has made air filtration units very popular, with some models hard to get. And it has led to a confusing cacophony of products and claims. Here is a simple guide to sensible selection of filtration units. While the guide is simple, the selection of the units is not simple, due to many misleading claims and unnecessary bells and whistles.
We suggest four criteria:
Be big enough – 100 cfm minimum.
Have true HEPA filtration.
Be quiet enough for a classroom.
Be a mechanical filter only – no snake oil.
1. Be Big Enough – 100 cfm Minimum
Manufacturers misleadingly claim large airflow rates that are possible only with noise levels comparable to those of a window air conditioner. And the actual airflow rates at lower fan speeds are usually not listed and not available. A rule of thumb is to assume that the actual usable airflow rate is a third to a half of the advertised rate.
Unless you are getting a unit for a small office, a flow rate of 100 cfm is a good minimum. If first cost is paramount, then you may find that multiple 100-cfm units will have the lowest cost.
2. Have True HEPA Filtration
HEPA (High Efficiency Particulate Air) filtration removes at least 99.9% of airborne particles of a wide range of sizes (0.01 – 10 microns, a range that includes the size of COVID-19 viruses). Lesser filtration efficiency also would be acceptable, but HEPA filtration is such a popular standard that more filtration units are available with it than without it.
3. Be Quiet Enough for a Classroom
We suggest a maximum noise level of 45 dBA. For most brands, compliance with this criterion is difficult to pin down prior to purchasing a filtration unit, due to the lack of published data. (However, see our Recommended Selections, below.) An ideal classroom will have even lower noise levels of 40 dBA or less, but this level is not achievable with HEPA filtration units except at very high cost per cfm, and background noise levels may be this high anyway.
4. Be A Mechanical Filter Only – No Snake Oil
With a 99.9% efficient filter, why would you need anything more? Answer: you don’t. You don’t need an air ionizer – or if your selected unit comes with one, just turn it off. Be aware that some units do not let you turn it off, so avoid these units. You don’t need Microban, silver nano-particles, or any other anti-bacterial treatment of the filters or any part of the unit. (The federal government rightly is discouraging the use of this class of products.) They have no effect on viruses in any case. You don’t need ultraviolet light, or photo electrochemical oxidation, or plasmawave technology, etc. You don’t need an “air quality sensor” measuring particles or Volatile Organic Compounds.
A carbon prefilter is fine – this removes gaseous organic chemicals, including odors.
Recommended Selections
Here are recommended selections that meet all four criteria. All of them have been widely available lately, and current shipping estimates are shown below.
• Honeywell HPA300, 100 cfm (our measurement) at 45 dBA (our measurement at 3 feet) on “Germ” (lowest speed), about $300, Energy Star Rated. (Ships in 7 days at Amazon)
• Blueair Classic 205, 140 cfm at 44 dBA on medium speed, about $400, Energy Star Rated. (Ships in 7 days at Amazon)
• Blueair Classic 605, 275 cfm at 44 dBA on medium speed, about $850, Energy Star Rated. (Ships in 5 days at Amazon)
Choice of Fan Speed
Use the selected quiet speed during normal operation. During mealtimes, when most masks are off, and the room is already noisy, run the unit at maximum speed = maximum airflow. (Notes on masks: N95 masks offer much better protection than cloth or fabric face coverings, and we have heard from teachers who keep their masks on while the students are eating.)
