It is essential to have a good air purification system in your home, especially if you have an HVAC system. The most common types of filters in HVAC systems are designed to reduce the concentration of particulate pollutants that originate inside the building or the air entering the building from the outside. These contaminants include dust, dirt, smoke, and mist, which generally range in size from 0.01 microns for smoke to several thousand microns for dirt. Gaseous pollutants such as ozone, nitrogen oxide, nitrogen dioxide, carbon monoxide, and sulfur dioxide are also present in the air.
While some are the result of the release of gases from synthetic materials found inside the building, most are introduced into the building from external sources through the fresh air intake of the HVAC system. Gaseous contaminants typically have a diameter of less than 0.01 microns. The most commonly used filtration system in the construction of HVAC systems is the mechanical air filter. Filters consist of spun glass or a thick nonwoven material that works through the process of casting and impacting particles with the filter material.
The speed at which the filter media removes particles from the air passing through it is the efficiency of the filter. Filters from different manufacturers have different efficiencies, depending on the design and construction of the filter. Fortunately, ASHRAE has developed a standard for testing filter efficiency, Standard 52.2, “General Ventilation Air Cleaning Device Test Method for Particle Size Removal Efficiency”. Filter designs that are tested using this standard are assigned a classification number called the Minimum Efficiency Report Value (MERV).
The higher the MERV rating, the better the filtration. For example, a filter with a MERV rating between 5 and 8 will remove 80 to 95 percent of particles in the airflow that are three microns or larger, while one with a MERV rating between 9 and 12 will remove 90 percent or more of particles one micron or larger. Filters with a MERV rating greater than 13 can remove 95 percent or more of particles 0.3 microns or greater. Mechanical air filters are effective at removing particulate contaminants from the HVAC system but cannot remove all contaminants.
For example, mechanical air filters do not affect gaseous pollutants. While HEPA filters are effective at removing particles in the 0.3 micron range, gases and vapors are 0.01 microns or less and require a gas-phase air filter to be removed from the air stream. Gas phase systems operate on the principle of adsorption, where atoms or molecules of a dissolved gas, liquid, or solid are chemically bonded to a surface. Activated carbon is usually used as material in gas-phase systems and they are usually installed with the HVAC system duct.
Stand-alone units are also available that can treat air in a particular area with a pre-filter installed in front of it to prevent solid particles from clogging it up. Neither mechanical air filters nor gas phase filters are effective against biological contaminants since biological particles are simply too small. But ultraviolet light of the right wavelength and in sufficiently high doses is effective in killing or deactivating many biological contaminants. The most efficient UV light system emits UV-C light with a wavelength of 200-280 nm and banks of lamps are installed inside duct networks to expose entire air currents to them.
The effectiveness of this system depends on several factors such as pathogen being targeted, volume and velocity of air in ducts, intensity of UV-C light, time pathogen is exposed to it and reflectivity of interior surfaces where lamps are installed. The Xiaomi Mi Air Purifier 3H is an elegant and minimalist device that fits well in almost any home equipped with a Class 13 HEPA filter that can remove 99.7 percent of smoke, dust, spores and fine particles from air. A challenge with this type of air filtration system is that it won't clean your entire home unless you live in a small apartment or small house; hence larger portable filters don't clean all air in your home either. The Philips 3000i Series air purifier may be your best home investment to date for best quality indoor air as it includes a HEPA filter (short for “high-efficiency particulate air”) which removes at least 99.97% of air pollutants down to 0.3 microns.
In addition, this model only filters moving air such as when heater or air conditioner is operating (although most HVAC systems have “fan on” mode that maintains air flow through ducts even when heater or air conditioner is not working). Unfortunately this also means that if you have an HVAC system that doesn't use forced air such as boiler or baseboard electric heating whole-house air purification isn't really an option for you; however room air purifiers with an authentic HEPA filter work best at removing smallest particles from room. The EPA, ASHRAE and CDC recommend upgrading air filters to highest possible efficiency compatible with system and verifying filter fit to minimize filter air bypass for best results when it comes to indoor air quality in your home; ideally best air purifier for your home should include HEPA filter along with other features such as activated carbon filter for gaseous pollutants removal and UV light for killing/deactivating biological contaminants.