These air cleaner plans and this discussion started as a way to help woodworkers, but then interest suddenly went crazy. Those who purchased particle meters found this air cleaner design quickly changes very irritating air to near hospital quality. Word got out in the asthma and allergy community that regular use of one of these air cleaners could stop the irritation long enough that people were getting well and losing their chronic conditions and sensitivity. Wild fires broke out all over the country and many more built these systems to help with the smokey air. Likewise, when the Covid-19 mess hit people built these air cleaners because they pull most of the airborne virus particles out of the air.
I worked with some cocobolo and other sensitizing woods that can create a bad allergic reaction in as little as four hours exposure and suffered a very bad reaction becoming extremely allergic. So much dust had contaminated my clean looking home that the only way I could stay at home was to be kept on huge amounts medicine to address my allergies. We did a massive cleanup. In my shop we used leaf blowers and large exhaust fans to keep blowing all off until no more dust settled overnight. Inside the home we upgraded the home vacuum to a HEPA quality filter, vacuumed all and then deep steam cleaned all the upholstery, drapes and carpets. Even after the cleaning, dust settled everywhere overnight and my allergies continued to flare. I replaced our HVAC filters with really fine filters and we had all professionally deep cleaned again and still had a problem with lots of dust settling. I then had to figure out what happened to our HVAC system as worked really well right after putting in the new filters, but after a little time our heating or cooling became terrible. I called my HVAC expert friend who has done my HVAC maintenance for over twenty years. He explained that finer filters at first move lots more air because the filter strands offer less resistance. Then, over time filters build up dust trapped by the strands that does not come out with normal cleaning. This is called seasoning and the greater the seasoning the better the filtering and higher the air resistance. Eventually a filter becomes saturated with as much dust as it can carry though a normal cleaning which creates what is known as a full seasoned filter. A fully seasoned filter can filter up to twenty times better than when clean and new and its resistance can be twenty times more than new.
The only way to move the same amount of air through seasoned filters is to upgrade a bigger, more powerful blower. In short, my fine HVAC filters seasoned which killed the airflow needed to heat and air condition my home. He told me to replace those very fine filters immediately because HVAC fan motors get their cooling from the air moving over the motors. Those extra fine filters so kill the airflow that our HVAC motors can burn up and even cause fires. I would have had to change out all three air returns to fit much thicker pleated filters with far more surface area plus upgrade to more powerful blowers to use finer filters. Instead, I put in the expensive electrostatic filters my HVAC expert recommended. They greatly reduced the visible dust in the home. Unfortunately, the particle counter I borrowed from the university where I taught showed almost zero difference in the fine airborne particle counts and I kept having bad allergy attacks at home unless I stayed heavily medicated.
My doctor convinced me to get a very expensive home air quality test. The inspector analyzed our settled dust and found it was almost all wood dust with a bit of dust from people and pets. His particle counter showed just walking through our thoroughly cleaned shop stirred up enough fine invisible dust to fail an EPA air quality test without any woodworking or turning on a single machine. His particle counter showed when we turned on the expensive top-rated cyclone dust collector and ceiling mounted air cleaner without doing any woodworking, these units had such open filters they saved up and blew fine unhealthy dust all over. During woodworking his particle counters showed the fine unhealthiest dust blew right my cyclone dust collector and air cleaner. These systems I installed to protect our health freely passed the fine invisible dust right through which caused it to build to dangerously high levels. He showed with his particle counter that every time we went through the connecting door into our home, we sent a huge amount of fine invisible dust into the home, plus we carried in even more on our clothes, hair and skin. The EPA found all types of fine invisible airborne dust are so unhealthy, that just a thimbleful of fine dust will cause a large home to fail an EPA air quality test. We continued to badly contaminate our home and since fine dust lasts nearly forever unless it gets wet, it just kept building. His particle counter showed even after our heavy cleaning our home's ceilings, walls, closets, cabinets, drapes, furniture, and carpets were all contaminated. He said our carpets were probably sitting on huge amounts of dust trapped between the carpets and pads. His particle counter verified this showing just walking across our carpets launched dangerously unhealthy amounts of fine dust. He said the only way I could reduce my allergic exposure was to replace the carpets preferably with a hard surface flooring, deep clean all and also install a good air cleaning system.
Wanting to measure our success, I spent a small fortune on a MetOne Aerocet particle counter, then went to work. We replaced the carpets with tile, had all the drapes and furniture deep steam cleaned again, and repainted the ceilings and walls. Exactly as our inspector predicted, there were huge dust pools between the carpets and pads. These efforts reduced our airborne dust level dramatically but not enough to avoid setting off my allergies. One of my engineer friends uses and recommended the Oreck air cleaners that were heavily advertised on TV. The two I installed made no dent in reducing the fine particle counts and captured very little visible dust probably because our electrostatic HVAC filters worked so well. I then added a pair of the Sharper Image air cleaners that another friend recommended. They also captured little visible dust and almost none of the fine unhealthy dust. Running all four units at once did not address the fine dust. Upkeep on these four units was a pain. The Oreck filters clogged constantly with the same nasty oily black gunk that covered the Sharper Image electrostatic plates. Even strong detergents worked poorly at cleaning this gunk off. One of my scientist friends at the Air Quality Board checked and found the black oily gunk was a mix of smog, household grease and dust.
Desperate, I bought an expensive Honeywell large free-standing barrel shaped air cleaner with multistage filter including both HEPA and activated charcoal layers. It looked impressive, cost lots, and had good reviews, but worked poorly as it had the same clogging problems. My particle counter showed it stirred the air poorly unless the HVAC was on, and just kept cleaning the same air over and over. With the HVAC on it took many hours to even make a small difference in home air quality. In short, just like my big shop ceiling mounted air cleaner, running the Honeywell and four portable air cleaners in the home only provided a false sense of security. They cost lots and made a lot of noise, but the particle counter still showed little to no reduction of the unhealthiest invisible dust.
This poor air cleaner performance convinced me to buy a central air cleaner system that connected onto my HVAC. That really expensive system worked poorly and its filters needed cleaned every few days and replaced often. The add on HVAC unit came with a small filter that quickly plugged, its auxiliary blower failed to move enough air, and my particle counter showed this unit passed the fine invisible unhealthiest dust right through. The firm that installed this unit and I went to war. They hated me because with my air volume meter and particle counter I was not fooled by the lack of visible dust. They insisted my "toy" meters did not work, so I showed them that my meter and the university meter I borrowed had been tested and recently calibrated by the California Air Resources Board. Their manager finally admitted my meters were better than theirs, pulled this system out and refunded my money. This is exactly what I went through with my magazine rated "best" cyclone. It created a bad false sense of security by removing the visible dust while building the invisible unhealthiest dust to dangerously high levels. It also lost the airflow needed to work because its undersized fine filter clogged constantly and cleaning that filter left a big mess of the very dust this unit was installed to avoid.
I decided I could use my spare large HEPA quality filters and big in-line duct fan to build a really nice air cleaner. My particle meter showed the result reduced the airborne particle counts down to safe which my ceiling mounted air cleaner never did, but it still took a very long time, meaning over six hours. I realized the problem was the same as with my Honeywell air cleaner. My new air cleaner failed to stir the air amply so it just kept cleaning the same air over and over again. I reversed my blower so it sucked through the filter and then blew out the top of the blower. The result worked much faster so that gave me the idea of putting a swivel duct on top of the blower to let me aim the cleaned air coming out of the filter so it stirred the whole garage shop area. The result worked really well taking only a few hours to get airborne dust levels down to safe.
This solution worked even better in my home. I put one of these air cleaners in our central cathedral entry and aimed the swivel duct up the stairs. This so well stirred and cleaned the air that just three hours of running a day brought the dust levels down to safe in my home which is much larger than my garage shop. Testing confirmed one of these air cleaners will amply clear the air for every roughly 2,500 square feet of living or office space in about three hours use.
I was so allergic that just a little dust would set off my symptoms but the particle counter showed just running this air cleaner for three hours a day in my home, kept the air quality excellent and I no longer had runny noses or watery eyes. This one air cleaner let me get rid of my five smaller air cleaners and safely go anywhere in the home. I no longer had to have up to six breathing treatments a day to keep my airways open. More importantly, after four years of my health declining, once I regularly ran this air cleaner, I was able to reduce my medications and my health started rapidly improving. Although I loved this unit, my family was not so happy because in our large open space home they could not listen to TV or music, or even hear each other without shouting when that loud blower was on. They started turning off my blower and the home immediately went back to dangerously high particle counts, so I had to run that air cleaner when they were not home or asleep. I bought a heavy-duty digital timer that ran this air cleaner every night for three hours. This turned out to be the right solution. I built this page showing how to build one of these.
Building one of these air cleaners is easy and affordable. These air cleaners got so popular that Wynn Environmental now offers the 9L300NANOEXT filter with the coating on the outside (exterior coating) to maximize performance and filter life and it is the more ideal larger 300 square feet size. That lets us build a really good air cleaner with just a filter, swivel duct, blower and a little weather stripping, plus optional timer and no need for a filter box as the air goes through the right way. This system uses a standard 8" diameter swivel duct on top of a 750 CFM 8-inch blower, on weather stripping on the filter to pull air through the filter then direct the fast-moving clean air stream to get good circulation.
Start with a big Wynn Environmental 9L300NANOEXT "nano" filter. It sits gasket side down on a large square of tile or another flat surface making a good seal below. On top of the filter apply a ring of 3/4" thick 1" wide self-adhesive foam insulation. On top of that just set at least a 700 CFM 8" in-line duct fan faced so it sucks through the filter and blows out the top. Remember you need to have the air go through from the coated side even if you need to build a box to enclose the filter. Inexpensive in-line fans are readily available but I found much better airflow and longer life with a higher quality in-line fan such as the fan shown here from Amazon.com. I also bought a heavy duty digital programmable timer so mine runs automatically every night when all are asleep. I manually run mine extra on weekends when the home tends to be most full.
My particle counters show it takes this air cleaner about 3 hours to pull the air down to safe for my large home. If I run the air cleaner every day then just over an hour a day keeps the air safe, but I still run the three hours a day to minimize my allergy exposures. We had some ugly fires that left our air so bad the sun was setting at 5 PM instead of 9 PM. I found running this air cleaner for three hours twice a day kept my home air quality excellent. In fact, my particle meter showed the outside air during these fires was over 50,000 particles per cubic foot but indoors inside my home I only had 200 particles per cubic foot.
Cleaning is also easy. About once a month put on the dual cartridge respirator mask, lift the blower off the filter, slip a big plastic garbage bag over the filter to keep from spreading the accumulated dust on the filter, take the filter outside, then use an air compressor attached long wand or vacuum on blow attached to a right-angle fitting. Then just blow from the inside out. I also blow my clothes and the outside of the filter off when done before going back inside.