Maintenance key to air filters' performance

We are replacing our furnace and are getting bids from heating contractors. A number of them have included add-on filters that the salesmen claim will take care of dust and make our home healthier. Is this true? Are these filters really worth the extra money they cost?
 
There are many air filters on the market today for central forced-air heating systems, some more effective at removing particles from the air than others. While some filters will help with house dust, most are more effective at removing smaller particles that remain airborne long enough to reach the filter.

“Dust particles are really pretty large,” says Roz Halstrom of Tri-Tech Heating (360-891-2002).

 “Visible dust is generally ten-microns or larger in size, which means it is heavy and floats down onto furniture long before it can make it to the furnace return. Most homes that are smaller than 2,500 square feet have only one return-air intake, usually located on the ceiling upstairs. That’s a long was for heavy dust particles to travel. Most of them never make it to the filter,” says Halstom. A micron is equal to one-millionth of a meter.
 
The size particle you want to remove will greatly determine the type of filter you install. Removing micro-sized particles requires a special filter. Larger particles, the kind you can see, can be removed by less expensive filters.
 
There are four basic varieties of filters on the market -- each with their own advantages and disadvantages.

Panel type filters, the standard filter on most furnaces, are designed primarily to keep the furnace itself clean and are designed to catch large particles. These filters are made of fiberglass or a “horsehair” material stretched across a one-inch frame. Panel filters are disposable and cost about a dollar at the local hardware store. They should be changed monthly.
 
Extended media or pleated filters can capture smaller particles. These filters have a large area of fabric that is pleated back and forth into a small space that significantly increases the surface area of the filter. Air is forced to go through more collection fabric than in panel filters, resulting in better filtration. The thicker the pleated filter, the more surface area and the more efficient it is at removing particles from the air. Homeowners should check media filters for cleanliness quarterly during the heating season and replace them once or twice per year. Expect to pay $20 to $50, depending on the filter.
 
HEPA (High Efficiency Particle Arrester) filters can trap very small particles -- less than one micron in size. A separate fan is used to divert a small amount of air from the return ductwork into a separate chamber housing the filter. After passing through the filter, the air is re-introduced back into the ductwork. A pre-filter removed large particles in the air stream that would quickly plug up the HEPA filter. Neglecting to clean the pre-filter regularly can cause premature failure of the HEPA cartridge and require replacement of the cartridge at a cost of around $200. Installed HEPA filter systems can cost more than $2,000.
 
Electronic air filters remove particles by attaching an electric charge to them. Particles are attracted to a plate with the opposite charge. This enables electronic filters to remove very small particles almost as well as a HEPA filter. However, unlike HEPA or thick pleated filters, electronic filters do not impede furnace airflow. Homeowners should clean these filters at least monthly to maintain their efficiency. Electronic filters will add $800 to $1,200 to the cost of your furnace.

Finally there are hybrid filters. These filters are relatively new to the marketplace and combine a media filter and electronic filter. They are very effective at removing particles from the air that make it back to the furnace. Hybrid filters can cost as much as a HEPA filter, but because they do not have same resistance to airflow as a HEPA filter, they do not require the additional ductwork of a HEPA installation.
 
All filters are only as effective as homeowners are at maintaining them. Routine filter maintenance is often neglected, significantly reducing a filter’s effectiveness.
 
“We find that it’s not so much which filter people have installed, but how well they maintain the filter,” says Halstrom.
 
“It’s very common to find filters at the register in the room. These filters are often neglected. Folks just forget about them. We still find filters out there that have been in the system since it was installed. They’ve never been replaced!”