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Dust in your home is made up of pollen, plant and mold spores, pet dander, lint, bacteria and other contaminants. Regular daily activities within the home such as dusting, vacuuming and cooking can increase particulate concentrations. Burning wood, gas, or smoking indoors are major sources of particulate matter.
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These particles, measured in microns, range in size from fairly large to microscopic. To better understand the size of a micron, note that a human hair is about 70 microns in diameter. The tiniest particles make up 99% of debris in the air circulating within your home. These can bypass the respiratory system's defense mechanisms such as the nose, sinuses and windpipe that filter out particles 10 plus microns in size and keep them from becoming lodged in your lungs.
Health effects from breathing particles can range from coughing, wheezing, and asthma attacks to more serious effects, such as decreased lung function, cancer, heart attacks, and premature death. They can also cause allergic reactions.
The best way to lower the particle count in your home is to keep sources of particles out of your home. For example, never let anyone smoke indoors. Make certain that stoves—including your kitchen stove—are fully vented to the outdoors. Keep pets outdoors if you have allergies to pet dander. Damp mop floors and hard surfaces to keep dust down. Keep humidity below 50 percent to reduce the likelihood of dust mite and mold growth.
After you’ve taken these steps, you can also use filtration to help remove more particles from the air. Here below is a discussion of types of filters and their place in keeping home indoor air clean.
Types of Furnace filters
Filters are disposable, reusable or refillable and are made from materials such as fiberglass, metal, manmade or natural fibers. They are designed to protect the air handling equipment, so it is important to keep them replaced as the manufacturer recommends. It is important to note that central filtration systems should be operated with the fan "on" for constant air movement through the HVAC system.
Factors that affect filter efficiency include fiber size, fiber density, airflow rate, and particle diameter. Manufacturers use a rating system to guide consumers to furnace filters that are the most effective at removing particles. Called a Minimum Efficiency Rating Value, or MERV rating, higher numbers reflect greater filtration capacity. Look for a MERV rating of at least 11 or higher.
• Panel filters, usually 1" fiberglass filters, are the typical furnace filters installed in the ductwork of most home heating and/or air conditioning systems. These filters do little to remove contaminants from the air. The primary function of these filters is to protect the fan and minimize the amount of dust on the heating and cooling coil. They also can capture large particles from the air. This basic filtering system may be upgraded by using a high-efficiency filter to trap additional pollutants (see below).
• Washable/reusable filters are designed to be washed and reused. They never get completely clean and can, therefore, become restrictive to air flow. These filters are ineffective at capturing small particles.
• Pleated filters are basically panel filters that have been pleated or folded to provide more surface area. These filters are typically more efficient than a panel filter by increasing the surface area for collecting particles.
• High efficiency pleated filters have an electrostatic charge that is designed to capture small particles and allergens.
• High Efficiency Particulate Air (HEPA) filters are extended filters that remove sub-micron [less than 1 micron in size] particles with high efficiency. HEPA filters consist of a core filter that is folded back and forth over corrugated separators that add strength to the core and form the air passages between the pleats. The filter is composed of very fine sub-micron glass fibers in a matrix of larger fibers. These types of filters are not designed to fit most standard furnaces; however, they may be a choice for new construction or system upgrade. They generally need a separate system consisting of a fan and filter. HEPA filters are comparable to a MERV 17-20.
• Electronic air cleaners use an electrical field to trap charged particles. Like mechanical filters, they can be installed in central heating and/or cooling system ducts. Electronic air cleaners trap a high percentage of particles from the air passing through them. These units also emit ozone. The American Lung Association recommends against using filters that produce ozone, even in small amounts.
Maintenance is key
When selecting a filter note that efficiency will change over time. As filters become loaded with particles, the available openings for air to flow through become smaller. The result is better filtration but less air movement, causing your furnace to work harder to move air through the system. Disposable filters need to be replaced on a regular basis to insure proper airflow.
Tips on using a furnace filter
• Read the manufacturer's instructions on maintaining your furnace to determine where the filter is located and how often you should have your furnace inspected by a licensed heating contractor.
• Identify from the instructions the type of filter appropriate for the furnace you have.
• When buying filters, look for the highest efficiency filter that works with your furnace (the higher the MERV rating, which is usually listed on the packaging, the better). Health House guidelines require a MERV rating of 11 or higher.
• Replace your filter at the stated intervals instructed by the manufacturer, usually about every three months, i.e., the first day of every season. Replace more often if you are introducing higher levels of particulates into your home, such as when renovations are being done. Also, consider more frequent replacements if you have a family member with asthma, allergies or another lung disease.
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