Interesting...
twocvbloke...your link showed EIGHT levels of HEPA filtration, mine showed FIVE.
The truth of the matter is that 95% or better filtration efficiency or better at 2.5 microns is going to be sufficient for the vast majority of allergy sufferers. A human hair is 100 microns or larger. Mold and pollen start at 1/40 that size. Every time an air handling system kicks on, a door or window is opened, or one ventures outside, more particles are encountered than can be filtered by a vacuum cleaner. A vacuum cleaner is not an air filter. It moves limited volumes of air at high velocity for the purpose of dirt removal, totally different from moving huge volumes of air at low velocity for filtration. No one has yet tried to market a true air purifier with attachments as a vacuum cleaner, (or home sanitation system) so why the reverse? Because people do not stop to think about what they are being told.
A 15 x 20 room with an 8 foot ceiling contains 2400 cubic feet of air. At a rate of 80 cu ft/min, it will take any device 30 min to process all the air in the room, provided all the air is processed, and processed only once. In reality, that does not happen. The air under the couch is likely not moved much from its place behind the fabric skirting. That air likely contains some of the highest concentrations of dust and allergens anywhere in the house. The air sliding down the wall and drifting under the couch drops particles and they cling to the carpet and the underside of the couch.
A high-filtration vacuum can be of great benefit to allergy sufferers, but the benefit comes from a thorough 'corrective' cleaning. while not spewing a ton of allergens and pollutants out the exhaust. An air purifier can help, too, but it cannot cleanse the environment of the buildup of allergenic debris.
HEPA has been used as a marketing ploy. Once filtration is 95% effective down to 2.5 microns, only the most severely allergic can tell the difference between that level of filtration and true HEPA.[this post was last edited: 3/26/2012-13:32]