Determine what type of filter your HVAC system requires. Check your system’s manual for reference. Be sure to purchase filters rated for residential systems, rather than ones rated for commercial use (See more on this in the “Understand Filter MERV Ratings” section below). You want to find a furnace filter that removes the greatest number of contaminants and has the smallest effect on air flow for your HVAC system. There are a number of different types to choose from, ranging in style and type of material.
The most commonly used types of filters are disposables. These are usually made of layers of material such as fiberglass, cotton, polyester or paper, encased in a frame that slides into an opening into the ductwork. There are also adjustable filters and sizes for non-standard openings, and washable filters that can be removed and cleaned. Washable filters usually require more maintenance than other types of filters, and often don’t have the same level of efficacy as disposables. Electrostatic filters use static electricity to attract and trap small particles and come in either disposable or reusable models.
Generally, a filter’s performance level depends on the density of the material it’s made of and the size, type and amount of particles that attempt to pass through it. Over time (from a month to three months, usually), filters collect enough particles that their material becomes dirty and clogged and begins to lose efficacy. This is when you need to replace or clean your filter. A filter that becomes too dirty restricts air when passing through and can make your HVAC system work harder than it needs to, which is inefficient and causes faster wear and tear.
Different homes and occupants may need particular performance from HVAC filters. Homes with many residents, pets, smokers and those with severe allergies require higher-quality filters than others. Generally, though, it's usually best to buy high-quality filters. While good ones may be a little more expensive, they will take out more pollen, dust and other irritating air particles than the cheaper filters. Consider using high-efficiency pleated air filters, which allow your furnace to pump cleaner air into your home, without undue strain on your furnace. The pleated design increases the filter's surface area, capturing more lint, dust, pollen, mold and mildew. Pleated filters don't need to be replaced as often as standard filters, but these filters should be replaced every three months compared to every month for economy filters.