In my last post I went on about why you need an air purifier.  In this one, I’ll let you what to look for when sourcing them.

First, they must have a filter…a filter that must be replaced periodically.  A big selling feature of some purifiers is that they don’t have filters, and hence have nothing that needs to be replaced.  But the fact is that dust, skin cells, mites, spores, etc…are constantly being produced.  So if nothing is taking them away, where do they go?  Nowhere.  They build up and stay in your home, to be stirred up and inhaled from time to time.  And by the way, those filter-less purifiers rely on ozone.  Read to previous post to get caught up about that.

They filter must have different components as well.  Here are the ones you are looking for;

1. A pre-filter. This is pretty standard.  It is usually a dark plastic mesh, and can be found on most air conditioners, purifiers, and some dehumidifiers.  If you’ve ever cleaned a filter off one of these, you know what I’m talking about.  The pre-filter is reusable.
2. A HEPA filter.  This gets the stuff out that gets through the pre-filter.  Please read the rating for your filter as well – you want it to remove 99% of particles down to 0.3 microns at 500 cubic feet per minute (cfm). This rating is very critical, as different grades of HEPA filter may not be as effective.  Remember that PM 2.5 (particulate matter that is smaller than 2.5 microns) is a very serious threat to your health, so a HEPA filter is a must.  Also, note the flow rate of the machine. I saw one about 6 months ago that had a HEPA with 99% efficiency rating to 0.3 microns at 500 cfm, but the minimum flow rate of the unit was 1200 cfm.  That’s 2.5 times the maximum flow rate for the HEPA to be efficient.
3. Activated carbon.  This is charcoal, a very established absorber of VOCs (volatile organic compounds).  Not all pollution in your home is particles – many are molecules, and need the pass through carbon to be removed.  Like the HEPA, there is a point where the carbon will become saturated and will need to be replaced.
4. A photocatalyst.  This is simply a compound that reacts in the presence of light to produced highly reactive molecules.  Huh?  Ok, remember those VOCs from above, well, because they are molecules of gas, some make it through the charcoal filter, and have to be dealt with another way. A photocatalyst, when hit with light, produces a compound called superoxide, which breaks apart chemical bonds.  So the evil VOCs, should they escape the charcoal, get broken into pieces by the photocatalyst.  And for the record, the preferred photocatalyst is titanium dioxide.
5. A UV light source.  Remember, the photocatalyst can’t work unless it is hit with light.  And UV light has the most energy making the photocatalyst more effective.  Also, due to its’ high energy, the UV light can break apart molecules itself by supplying the needed energy directly.  So those nasty VOCs have to run a 3 step gauntlet, and there is no escaping light.

Of course, the explanations can get a lot more technical, but that’s the gist of it. You need those components for your air to truly be clean.  I hope it’s obvious that things must be physically removed from your air, and ease of maintenance should not be a deciding factor when purchasing.

Also, please note the square footage requirements.  Even if rated up to 3000 square feet, I’d say to be safe you probably want one every 1000 square feet or so. To put it another way, if the purifier is on the main floor, how much of the master bedrooms’ air do you think it circulates?

I hope this helps you find in your search for air purifiers.

Anyway, Happy Holidays and see you in 2010!