Air 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. Keeping the filter clean helps prolong the life of your heating and air-conditioning unit.
These 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.
Depending on the type, filters are capable of capturing dust mite debris, mold spores, pet dander, smoke, bacteria, dust, pollen and more.
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. 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.
Air Filter Types: Size, Shape, Material and Style
The first thing you need to know is the size of your air filter. Simply check the existing filter to get the dimensions. There's nothing worse than thinking you know it, and then getting to the store and drawing a blank. Most filters for residential HVAC systems are 1-inch thick, but some houses require up to 4-inch filters because of the volume of air circulating in the home.
Adjustable filters are available for non-standard ventilation openings. Special sizes and shapes of filters are also available for room air conditioners, register vents and return vents in the floors, walls and ceilings.
There are several choices of material and style to choose from when buying a home or 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 (most often fiberglass), in some cases covered by a honeycomb-shaped grille.
Pleated filters 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.
Air Filter MERV and MPR Ratings
Most filters are labeled with a Minimum Efficiency Reporting Value (MERV) rating number, which measures a filter's ability to trap particles ranging in size from 3.0 microns to 10.0 microns. A residential air filter commonly has a MERV rating of 1 to 12. The higher the MERV rating, the more efficient the filter is, and the more particles it can filter. 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.
MPR (Microparticle Performance Rating) is one example of a vendor-specific rating system. MPR is a measurement of efficient capture of particulates, such as bacteria and smoke. As with MERV, a higher number indicates higher efficiency