When you purchase higher-cost filters, you’re getting a filter that requires less changing and captures more, and smaller, particles. The $1 woven fiberglass filters do one thing—screen out dirt and debris that could damage your furnace blower motor, though they do take out some pollen and mold spores. If you can remember to swap them out every month and air quality isn’t an issue, these will do the job.
But if you’re the kind of person who forgets to change the oil in your car, buy $4 pleated filters, which require changing only every three months. If you stretched out the accordion-like material in these filters, you’d find two, three or four times the amount of surface area. This means they can capture smaller particles for longer periods of time without impeding the air flow of your furnace.
If members of your household smoke or have allergies or asthma, or if you have pets, look into the more expensive, high-efficiency electrostatic filters—ones that both filter and magnetically attract contaminants. Some are effective for up to a year. They can filter out bacteria, dander, odors and smoke particles. But health experts warn that you may be wasting your money on these $20 to $40 filters unless you take the following steps: Use them in conjunction with a high-efficiency vacuum cleaner, install a dedicated air purifier, wash or vacuum the filter monthly and take other steps to clean up your air and house as well.
Many filters carry a MERV (minimum efficiency reporting value) rating, which indicates their effectiveness. The higher the MERV rating, the more effective. Most spun filters have a MERV rating of 4. Standard pleated filters average MERV 6. Electrostatic pleated versions start at MERV 8, with the highest quality ones hitting MERV 12.