So far, we've heard about the importance of improving indoor air quality with air purifiers at topairpurifier.org. We know that breathing fresh air is good and the air in the room is ... often not so good. Even in large and busy cities, indoor air is two to five times more polluted than outdoors. You're crazy, right?

Chemicals in household cleaners and fragrances are said to have the potential to reduce air quality. We know that our shoes can bring allergens and other contaminants into the home. And we know that we spend a lot of time breathing these pollutants indoors.

And I feel the effect. These contaminants from sneezing, throat scratches and dry eye can bother us for months. They also help our colds and allergies. To make matters worse, long-term exposure to these common pollutants is dangerous and can cause a variety of lung-related illnesses.

What does HEPA mean?
Filters are one of the key components of air purifiers. The type of filter is defined by the size and amount of fine particles that escape the air passing through the filter. Microscopic particles are measured in microns. The last period of this sentence is about 400 microns. 30 micron pollen grains, about 20 micron house dust mite particles, and about 1 to 20 micron cat allergen particles vary in size.

The HEPA (High Performance Particulate Air) filter removes 99.97% of all small particles down to 0.3 micron from the passing air. However, keep in mind that these percentages are related to the air passing through the filter, not necessarily all the air in the room. Many ads give the misleading impression that HEPA filters clean the air in rooms that make up more than 99% of the particles. In fact, the amount of clean air in a room depends not only on the filter, but also on the amount of air that passes through the filter. This is known as the "Clean Air Delivery Rate" or CADR. Both the Environmental Protection Agency and the American Lung Association recognize CADR as an appropriate test for the effectiveness of air purifiers.

What does CADR mean?
The clean air supply rate is a measure of the amount of particle-free air that enters a room. This is the best measure of the true cleaning capacity of an air purifier as it reflects both the efficiency of the filter and the amount of air that passes through the filter. The higher the clean air supply rate, the larger the room size and the more effective the removal of particles in the air. Clean air supply rates are measured using methods standardized by the Association of Home Appliance Appliances (AHAM). This allows you to compare different capacities of air purifiers. Please note that most air purifiers have multiple fan speeds and the advertised clean air supply speeds are applied at the maximum speed.

The Medify MA-50 is a powerful air purifier with a true HEPA filter. Large-scale filtration is a relatively compact design due to the efficient design of a central fan that draws air through filters on all four sides.

The Medify filter is HEPA13 rated, a highly efficient type often used in medical facilities, and is effective in removing airborne particles that spread the SARS-CoV-2 virus.

The disadvantage of high quality filters like for dyson air purifier at https://www.topairpurifier.org/category/dyson-air-purifier/ is the high annual cost of replacing the filters because they are expensive. Also, the better the filter, the more airflow will be blocked. This means that the fan is strong enough to allow air to pass through the filter and the fan needs to be larger at higher settings. Expensive filters and powerful fans are the hallmarks of all high capacity HEPA air purifiers.

Designed for large spaces, the MA-50 is ideal for open-plan homes and offices. Fortunately, Medify also has a variety of air purifiers for smaller spaces with the same HEPA filtration rating. These are Medify MA-40, MA-25, and MA14. I didn't test the small unit directly, but a similar filter design should give high performance.