It isn't just dust. Eighty percent of household dust is actually dead skin cells from us and our pets, and the feces from dust mites that eat that skin dander. Most of us are not greatly affected by this "dust", some of us suffer from sneezing, runny nose, and headaches from just a minute amount of this stuff floating in the air. What has this to do with vacuum cleaners? Plenty, it turns out.
Filtration is the most important consideration here. HEPA (High Efficiency Particulate Air) filters on the exhaust of any vacuum will help trap the microscopic particles that carry everything that sets off your allergies. You need to make sure that the filter is sealed. Sealed means that the air is forced through the filter, and cannot go around the filter. HEPA filters that are not sealed are as bad as not having one at all, because all the air will go around the filter, as it is the easiest path. All HEPA filters are made out of the same material. They come in different sizes and shapes, but they do the same job, as long as they are really sealed filters.
Almost no HEPA filters are washable. Some manufacturers say they are, but it is like trying to wash a paper plate. They crumble and disintegrate. Most HEPA filters can be cleaned, at least partially, by using an air compressor to plow out the filter. Just make sure the dirty side of the filter is pointed away from you. Otherwise you will actually force the dirt further into the filter.
Most HEPA filters need to be changed once a year. This can vary widely depending on how often you vacuum, if you have pets that shed, and how much carpet you have. Carpet traps and stores dirt, and also stores the dander and microscopic mites that feed on that dander.
What is the vacuum cleaner casing made from? There are different grades of plastic. The cheaper vacuum cleaners are made from ABS which will warp if it gets hot enough. This warping will allow dust to bypass the filters and spew out into the air we breath. This is one of the main reasons vacuums lose their power after several years. The motor is still in good shape, but the air is leaking out into the room, bypassing the filters. The air is also being sucked in from places on the vacuum bedsides the nozzle on the floor. This warping is also why you will find dust collecting on the outside of you vacuum cleaner after a few years.
Amazingly, the motor material helps with the allergies. A metal motor in the vacuum cleaner will dissipate the heat from inside the motor. A cooler motor will not heat up the plastic enough to warp it. Your filtration will be kept sealed and functioning.
A charcoal filter in your vacuum will also help with the filtration as well as keep pet odors to a minimum.
Cleaning your carpet regularly, perhaps once a year, will freshen the carpet. We suggest using hot water extraction carpet cleaners. They do a more thorough job than the dry foam method, although they can make a mess if you don't use the cleaner properly.
Bagless vacuum also can cause an airborne allergen attack when you dump out the container. We suggest using HEPA filter liners, or Micron Filtration liners to hold the dirt. They make less of a dirty mess when you dispose of them.
I hope this helped.
