Air Purification Systems

Besides a ventilation system, another component of good indoor air quality is an air purification system, which filters and purifies air through a duct system. You can significantly increase the air quality in your home at a low cost simply by installing a better return air filter system.

One indication of air quality is the minimum efficiency reporting value rating—the MERV rating (Minimum Efficiency Reporting Value)—which measures the effectiveness of air filters on a scale of 1 to 16. A filter rated at 16 will capture more than 95 percent of airborne particles on a single pass through the filter. However, this level of efficiency doesn’t allow air to move freely within the system and actually results in a decrease in the system’s overall efficiency.

A good media filter has a MERV rating of 10, which effectively removes most of the larger dust particles from the air without significantly impeding air flow. An electronic air cleaner can be added to boost the MERV rating to 13, but these use more energy and require regular maintenance to operate well.

High-efficiency particulate absorbing (HEPA) filters with a MERV rating of 16 are also effective air cleaners, but they are usually installed in a separate branch of the duct system. They can impede air flow too much to be added to a normal return air duct system.

In addition to filtering air, you could install a biocide chamber, which uses ultraviolet (UV) light to actively kill bacteria, viruses, and mold spores in the air. These particles still need to be filtered out of the air, but at least they won’t reproduce.

The last variable regarding indoor air quality is the humidity, or moisture content, of the air. A building with about 35 to 40 percent relative humidity will feel comfortable without drying out skin and nasal passages. That level of humidity isn’t high enough to support active mold growth. A building’s humidity can be controlled through mechanical ventilation devices, but whole-house humidifiers and dehumidifiers can also maintain the preferred humidity level in your home.

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