After an exchange about hydroxyl air purifiers, Mike asks another question:
"What is your opinion on purification units with HEPA and carbon filters versus the hydroxyl technology. I am reading a lot about fine particle pollution I.E dust and I notice that this (hydroxyl) technology does not eliminate the particles although it does appear to neutralize particles. Can you speak to this issue?" ---Mike
Fine particle filtration is certainly a common part of air quality but there are some critical things you need to know about filters.
First, do you have a dust problem, or have you just read about it, and do you know the source of the problem, or it is just general household dust? If you know the source, like specific outdoor pollution, it is best to block (or filter) the source. For instance in my neighbourhood we have a serious winter wood heating smoke problem from 13 chimneys surrounding my house – so I use a commercial grade activated carbon filter on the fresh air line of the air changer but only in the winter.
Actually most of the dust in your house is recirculated dust. If you put a HEPA filter on your vacuum cleaner, or better yet, use a central vac with an outdoor exhaust, no expensive filter needed, you will remove more dust than a ventilation system can -- which may be enough to not need all those expensive filters.
Second, understand how air filtration works. Even if you are promised 99.9% particle capture with a HEPA filter, understand that is 99.9% of the particles that actually hit the filter. Only a small portion of the household, or room air actually go through the filter. This is true even with a forced air heating system. That filtered air then mingles with the room air and only a small portion of that mix get filtered in the next pass through the HEPA filter. You can visualize this dilution process by taking a clear glass of coffee, pour out about ¼ of the coffee and refill the glass with water and mix. The mix is now less black. Do it again, and again. It will take a long time before the dilution process resembles anything like a clear glass of water. And if you put back just a little black coffee, you are back into the middle of the process. Air filtration does dilute dust but does not eliminate it. It dilutes it enough that people appreciate it, but from a health point of view it is not the miracle it is sold to be, unless you are filtering at the source of the dust and the dust never gets into the house.
Third, high density filters like HEPA and Carbon do collect dust, which causes them to clog up much faster than other less efficient filters. Actually, that is what we want, trap the dust, but it means that you have less and less air flow as it gets clogged. High density filters actually cost more to operate because they require stronger fans to push the air through, even before they start to clog up. That is not significant in a modest size residence but is a major problem for commercial and institutional spaces, like schools.
Fourth, high density filters do collect both organic dust and microbes, more so than ordinary filters, and if not changed regularly become a breeding ground for microbe and mould growth – right in the middle of your ventilation system. This is especially true of the carbon filters. Placing a hydroxyl generator upstream of the filter will constantly disinfect the filter; the filter will still get full of dust, but it will not be biologically active dust. Now you have a great combination of dust control and sanitation. Some stand-alone units promise both but you will find they are basically filter selling companies with an inadequate shot of hydroxyl.
A germicidal UV lamp inserted in the ductwork will kill some microbes in the air-streem but has no effect on what gets past the lamp and collects on the filter. Hydroxyl sanitizes both the airstream and all surfaces downstream or in the room where the air is delivered.
Fifth, high density filters cost more and must be replaced more frequently that less efficient filters – hence the question, do you really need fine particle filtration where you live? For some people, they are an expensive essential – for others an unnecessary expense.
Ion generators are also sold as air sanitizers and dust cleaners, without the filtration problems. I love negative ion generators first for the stimulating effect all those electrons have on human health, then for their sanitizing action as well, but as for the dust, you must ask the question, “Where does the dust go?” Actually, it gets charged with static electricity and sticks to the first surface it hits: walls, furniture, floors. You do get cleaner air but you have to clean your walls, even ceilings several times a year – and when you walk on that dust on the floor, it just floats back up into the air. I have two small negative ion generators running in my office all the time which help to keep me alert in my old age, but my wife will not allow them in the nicely painted bedroom.
The Pyure high performance hydroxyl generators use the ventilation system filters when inserted into heating or air change ductwork, even keep those filters sanitized, and have simple washable cat hair filters for the stand-alone portable units. Any inexpensive filter system could be used alongside the hydroxyl device, and you won’t be turning the hydroxyl off because you are tired of paying for high density filters.