Choosing a Home Air Filter

Clean air is just as important inside the home as it is outdoors. The filters used with an heating and cooling system make a big difference in the quality of air circulating throughout the house. Choosing the right filter ­ and changing it regularly ­ will help your family breathe more easily.

Filter Basics

Home air filters ­ also commonly called "furnace filters" ­ keep the coils and heat exchanges on the heating and air conditioning system clean. Dirty coils and heat exchanges make the system work harder, so keeping the filter clean helps prolong the life of your HVAC unit.

Of course, the filters also clean the air that you and your family breathe. The variety and amount of particles in your home's air will depend on how many people and pets live in the house and what types of activities go on there. People with allergies or asthma should be extra diligent about keeping home air filters clean.

The most important thing to remember about home air filters is to change them regularly. Even the highest-quality filter can't do its job right if it's clogged with a thick layer of particles it's been filtering from the air. Different filters are meant to be changed at different intervals, but once a month is a common time frame. Brand new homes, as well as homes where there is remodeling or construction going on, will need more frequent filter changes to compensate for the extra dust and residue in the air.

Good idea: Schedule your filter changes to coincide with another regular household activity, such as paying a monthly bill or giving pets their flea and heartworm treatments. You'll be less likely to forget if the two activities are linked in your mind.  Or use our Email Reminder Service to receive periodic emails reminding you to change your filter.

Fiberglass Filter.

Pleated Filter.

Material and Style

There are several choices of material and style to choose from when buying a home air filter. Performance is affected by the size and density of the material used, as well as the size and volume of the particles being filtered.

The least expensive filters have a layer of fibers, in some cases covered by a honeycomb-shaped grille. The material is most often fiberglass.

Pleated filters ­ made of a variety of materials ­ are more efficient because the pleats provide a greater surface area to trap particles. Many pleated filters are electrostatically charged to help them attract and hold microscopic particles.

Reusable filters are made of material that can be rinsed clean with water.

Some filters for window air conditioners are made of foam.

Minimum Efficiency Reporting Value (MERV)

Most filters are labeled with a MERV rating number, which measures a filter's ability to trap particles ranging in size from 3.0 microns to 10.0 microns.

Residential filters commonly have MERV ratings of 1-12. The higher the MERV rating, the more efficient the filter is, and the more particles it can filter.

• A MERV rating of 6 means the filter is 35% to 50% minimum efficient at capturing the measured particles.
  
  
• A MERV rating of 8 means the filter is 70% to 85% minimum efficient at capturing the measured particles.
  
  
• A MERV rating of 11 means the filter is 85% to 95% minimum efficient at capturing the measured particles.

MERV is an industry standard rating, so it can be used to compare filters made by different companies. Some manufacturers also have their own rating systems.

Size and Shape

Most filters for residential HVAC systems are 1" thick, but some large houses (3,000 sq. ft. and more) require 4" filters because of the volume of air circulating in the home. The 1" filters come in a variety of sizes, so be sure to note what size you need before going to the store to make a purchase.

Adjustable filters are available for non-standard ventilation openings. Special sizes and shapes of filters are available for room air conditioners, as well as for register vents and return vents in the floors, walls and ceilings.

Good idea: Buy furnace filters several at a time, so you'll always have one handy to make changing convenient.