Although Los Angeles is not exactly known for its fantastic air quality (read: LA air sucks), the move to a colder climate and relocation to the Willamette Valley (which is known for it's many species of face itching sneeze making grasses) has somewhat inflamed the allergies of my wife and I. That being said, we have been very active recently trying to minimize our exposure to allergens and keep our indoor air as clean as humanly possible.
Indoor Air Quality is a section of green building that is often overlooked by most people (though architects and building professionals are likely to spend a good deal of time thinking about it). It is not as flashy an issue as global warming, habitat destruction, etc. But it is very important to our health and well being, and our ability to be productive and happy. As an allergy sufferer I can tell you, if you are not breathing properly when you sleep you feel like a zombie the following day, and all productivity and hope of happiness goes out the window. All you can do is shuffle along and think about biting anyone who gets close to you. In our research, we were somewhat surprised to discover that the air purifier we had been using was not actually doing anything useful.
HEPA filters are extremely efficient at arresting tiny particles in the air, measuring only micrometers in diameter. It is illegal for filters to be advertised as HEPA if they are not capable of arresting those tiny particles. However, for some unfathomable reason, cheaper filters which do not arrest any allergen particles at all can be called "HEPA Type," "99% HEPA," or "HEPA like." The Hunter purifier which Courtney bought many years ago was just such a product. So, we concluded that we needed a new one, with a "true HEPA" filter this time. Although I generally advocate getting stuff used as often as possible, when it comes to an issue of personal health you get the best product available.
In researching air purifiers before making a purchase, we were shocked to discover that the Ionic Air Cleaner types were basically worse than useless for allergy sufferers. They mask odors and make the air smell fresher by producing Ozone (O3). Now, while Ozone is a great thing in the upper atmosphere, where it filters UV light from the sun, here in the atmosphere that we breath Ozone is a very, very bad thing. It is toxic to pretty much all living things, including plants, animals and us. And while a little Ozone won't kill you, it will irritate your lungs and sinuses, exacerbating any symptoms of respiratory tract infection or allergic reactions. So in other words, they make your allergies and your indoor air quality worse. As if that wasn't bad enough, Ozone in the troposphere (where we live) is a green house gas, and unlike CO2 and other green house gasses, it can react with other pollutants to generate more Ozone in a cyclical reaction. In case you didn't get the message, do not purchase Ionic Air Purifiers or Air Cleaners, they are all but evil.
In summation: if you want an air purifier, get a true HEPA filter sized to the room that it will be in. Courtney and I got a Honeywell 50250 Round Air Purifier for the living room, and a smaller, quieter Honeywell 17000 HEPA QuietCare Air Purifier for the bedroom. Both came with permanent true HEPA filters. We have been sleeping much easier since. I really cannot overemphasize how awesome these things are. Since we purchased ours, we can't smell the cats litter box except for two seconds right after an "event," we don't have to dust as often, and I wake up feeling like a real human being, even when I forget to take my Aller-tec.
Aside from the air purifiers, we have a Dyson Ball vacuum with a HEPA filter, several house plants that filter specific VOCs out of the air (see this website), and do everything we can to reduce the amount of dust and other allergens in our home. It is a constant battle, but for now one we are winning quite decisively. Unfortunately, running two fans 24-7 means more energy consumption, but since our local utility (SUB) generates 80% of its energy from hydro-electric, I don't feel quite so bad about it.
Editing this, I realize that there are a lot of ads in this post, but learning how to control my allergies was a struggle for me, and I think that promoting the products that I found most useful in controlling my symptoms is an important thing to do. So I am unashamed about all the ads in this post, in other words. And no, I don't work for Honeywell (though if they wanted to pay me for the plugs I wouldn't complain).