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The Basics of Air Filters

It’s the most basic maintenance you can perform for your furnace or air conditioner, but it’s also one of the most essential. A clean air filter helps deal with allergens floating throughout the home, limits the spread of mold spores, and helps to improve the efficiency of your central air system by limiting dust accumulation in the ventilation system itself.

Air filters are in more than just your home. Your car has one for its HVAC system as well and, just like in your home, keeping this air filter clean helps to improve the efficiency of your engine. When a filter becomes dirty or clogged it builds up backpressure. Everything in a ventilation system that impedes air flow (resistance to airflow if you will) forces the blower fan to work harder.

When the blower fan has to work harder to push air through the ventilation system (moving past a blockage), it takes more energy to move the same amount of air. But there’s an added decrease in efficiency at the heat exchanger. Air conditioners operate by removing heat from the air. If the air can’t move, the heat exchanger has nothing to remove, which affects the entire HVAC system. All of this is simply because a dirty air filter makes it difficult for air to pass through your ventilation ducts. A quick change of your filter will allow air to move freely through the system. This is why you should change your filter every 3-6 months based on how often you use your central air system.

Filter Types

Filters are rated based on how well they filter out particles and pollutants with a Minimum Efficiency Reporting Value (MERV). The higher the MERV score, the better a filter is at removing pollutants from the air. If you suffer from severe allergies, a higher MERV rating is a good idea. If allergies and dust are not a problem for you, then a lower score won’t be an issue.

Typical filters are:

  • Fiberglass
  • Pleated Polyester
  • Electrostatic
  • High Efficiency Particulate Arrestance (HEPA)

Fiberglass and polyester filters are fairly inexpensive. In fact, most filters used in modern homes are fiberglass filters. These filters do a base-line job of keeping your air clean, and are perfectly suited for most people when replaced regularly. Pleated polyester filters are slightly more expensive but the change is significant. The pleats (folds) in the filter increase the overall surface area. With a higher surface area, there are more spaces for the filter to trap contaminants and airborne particles. If you have pets, a pleated filter is not a bad idea.

Electrostatic filters are a good upper-range disposable filter. They have a decent MERV rating and can be a simple upgrade to help improve allergy symptoms when dust, pollen, and pet dander are a problem. Unfortunately, they’re usually more expensive than fiberglass and polyester filters. While the latter are usually $1-2, electrostatic filters are often $10 at their cheapest. Then again, that’s not a terribly expensive cost for easy breathing year round.

HEPA filters are not common in homes. They’re expensive and extremely large in size. HEPA filters require special installation since they are not a standard size and are much thicker than a traditional home filter. They’re usually used in medical and clean room applications where extremely clean environments are mandatory. If you suffer from severe allergies or breathing complications, a HEPA filter is worth the installation costs for clean, easy breathing at home. As an added benefit, HEPA filters only need to be replaced annually instead of every three months. A higher expense, but they do feature the highest MERV rating of any filter.