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Asthma and Air Filters


Types of Air Filters continued...

"Ultra-HEPA" room air cleaners are available, which remove even higher proportions of very small particles. There is no convincing evidence that they are more likely to improve asthma control when compared to conventional HEPA air cleaners (with a similar CADR, see below).

Electronic air filters use electrical charges to attract and deposit allergens and irritants. If the device contains collecting plates, the particles are captured within the system; otherwise, they stick to room surfaces and have to be cleared away.  A disadvantage of these units is that almost all of them create small amounts of ozone. Ozone irritates airways, causing temporary bronchospasm in those with asthma, and nasal congestion in those with hay fever or rhinitis.

Hybrid air filters contain elements of both mechanical and electrostatic filters.

Gas phase air filters use activated carbon granules to remove odors (volatile organic compounds or VOCs) and non-particulate pollution such as cooking gas, gases emitted from paint or building materials (such as formaldehyde), and perfume. These thin black filters are often placed in front of HEPA filters. A disadvantage of these filters is that they quickly become ineffective as they absorb a load of fumes, so they must be replaced as often as every month.  However, they are relatively inexpensive. An advantage is that they remove large particles (acting as a pre-filter), thereby increasing the life span of the expensive HEPA filter.

Germicidal air cleaners use ultraviolet (UV) lights to kill bacteria, viruses, and molds that pass through the area with the UV light. Such UV lights can be included with other air cleaner devices, which use a fan. We are unaware of any research demonstrating that the addition of germicidal UV lights improves respiratory symptoms in people with lung disease. However, they have been used for decades to reduce the risk of infection with tuberculosis among staff and visitors in hospitals who are actively treating such patients.

Ozone generators are devices that intentionally produce high concentrations of ozone to clean the air in a room. They are often used to decontaminate rooms after smoke exposure following a fire. Ozone causes bronchospasm in people with asthma, even in low concentrations, and thus should be avoided. 

Whole-house air cleaners may be used if your home is heated or air-conditioned through ducts. With a whole-house air cleaner, HVAC system includes air filters designed to reduce the accumulation of dust and dirt in the ducts and coils of the system. These simple filters cost less than a dollar each to replace every month or two, but they only remove large particles, not the small particles in the house that are inhaled into the lungs. You can buy more efficient replacement filters (usually for 6 to 20 dollars each) which will remove many smaller particles.  These are often pleated or coated with an electrostatic charge. However, these replacement filters clog quickly in dusty environments, reducing airflow through the system, causing a reduction in the heating or cooling efficiency.

Permanent whole-house air cleaners can be added to an HVAC system, but the cost is several hundred to a few thousand dollars for the unit and the installation. Disadvantages include the ozone byproduct of electrostatic air cleaners; the need for frequent cleaning of the plates; the need to keep the fan running continuously (24/7) to clean the air, and the electricity cost and noise associated with the large blower fan running continuously. 

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