When you think about air pollution, the last place on earth you expect to find it is in your own home. However, according to the U.S. Environmental Protection Agency, indoor air pollution can very well be two to 5 times higher - and some of the time more than one hundred times as high - than levels outside. That means poor indoor air quality is one of the top risks to our family's health. Since we spend 90% of our time inside buildings, that puts us in a bind.

HEPA (High Efficiency Particulate Arresting) filters are one possible answer for better indoor air quality. HEPA filter technology has been used since the 1950s when the US Atomic Energy Commission thought it important enough to purge tiny radioactive particulates from the air.

HEPA filters work something like this: think about one sheet of HEPA paper (really it's made of a paper-like fiber or polymer) with very small holes that filter out contaminating substances. Inasmuch as the surface area is restricted, only very limited amounts of air are able to flow through. If the size of the sheet was doubled, it would be possible to get two times the airflow and 2 times the filter life.

A larger surface area would result in a more productive filter. So in place of increasing the total size of the sheet itself, the surface area is increased by being folded back and forth a number of times. Some filters have as much as forty square feet of filter material. HEPA material is actually a rather astonishingly thin bond of fibers.

Air is forced to go through this elaborate network of fibers and in the process, the damaging particles hit the fibers and stick. HEPA filters naturally filter out bigger sized particles like dust, however they also work efficiently against mold spores, viruses and bacteria.

All types of air purifiers report that they clean 99.97% of the air that flows through the HEPA filter - but what they don't disclose is that some air doesn't flow through the filter. If the air doesn't go through the HEPA filter then evidently it isn't filtered. That makes the issue of 99.97% efficiency somewhat questionable.

The best HEPA filters don't have a problem in this area because their designs include fans that really push air through the filter - the more air that passes through the filters, the cleaner the air becomes.

The size of the room is an important consideration when determining the size the air purifier should be. Evidently the bigger the room is, the bigger the filter ought to be. An additional thought is to have 2 smaller filters. They can divide up the work - and allow 2 times the amount air to make it through the filter.

Remember that HEPA filters do not filter out chemicals, gasses and odors. That's because these molecules are too tiny compared to HEPA's 0.3 micron holes. In order to filter out these damaging molecules, some type of substance is key to absorb them - activated carbon is generally used.

Don't be afraid to ask questions when it comes to deciding which air filter to get for your family's health. Reputable dealers know about their brands and can best suggest which size of filter is necessary to guard your home and ensure it's healthy and clean.