The Dirt on AIR FILTERS

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Generally, mechanical filters are efficient at collecting large particles, but remove a small percentage of smaller particles (the panel filter is somewhat more efficient at small-particle capture). With mechanical filters, the more dense the filter material or the greater the filter surface area, the better it will remove pollutants. Whole-house mechanical filters, at $1 to $15 each, are a bargain in the air-cleaner world, but they are also the least effective, stopping only 10% to 40% of pollutants. They also need to be replaced on a monthly or bimonthly basis.

Electronic air cleaners are the most efficient cleaners of indoor air, removing up to 95% of dirt, dust and smoke.

I on generators, which come as portable units only, use electrostatic charges to remove particles from indoor air. The charged particles in a room are then attracted to walls, floors, tabletops, draperies and occupants, which often results in a noticeable accumulation of soot. In some cases, these devices contain a collector to attract the charged particles back to the unit. They may also have a fan and mechanical filter. Ion generators take second place in the price hierarchy, at $50 to $150 apiece, but you usually need a unit for each room. Also most systems require either filter replacement or periodic cleaning. They can remove 25% to 94% of the pollutants.

Electronic air cleaners use an electrical field like a powerful magnet to trap charged particles. Whole-house air cleaners are most often installed in house ducts between the cold air return and the fan, but they can also be in portable units with fans. Electronic air cleaners are usually either electrostatic precipitators or charged-media filters. Electrostatic precipitators collect particles on a series of flat plates, or cells, enclosed in a metal frame. There are nonelectronic electrostatic precipitator filters, but these are not as effective. Charged-media filters, on the other hand, collect the particles on the fibers in a filter.

Electronic air cleaners are the most efficient cleaners of indoor air, removing up to 95% of dirt, dust and smoke. They are also the most expensive, ranging in cost from $150 to $600, with some units costing upwards of $1,000. One big advantage to electronic air cleaners is that they can be reused almost indefinitely, needing only to be washed in the dishwasher or tub.

Finally, hybrid filters - those that combine all three types of cleaners - may be whole-house or portable, and can combine different methods such as mechanical filters and passive electrostatic filters. These can range in price from $50 to $200 and often require expensive filter replacements on a periodic basis. Their effectiveness varies depending on the combination of filters.

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