Homeowners expect their houses to be warm in winter and cool in summer, but don’t take those comfortable temperatures for granted. Regularly changing the air filters is an essential task.
HVAC systems move air in a continuous loop through the house. An intake vent uses a fan to pull air from the room through a duct system and blows it across a heat exchanger in the furnace for winter, or an evaporator coil for cooling in summer. A filter cleans dust and other particles out of the air being drawn into the system through the intake or “return” air vent. Without a filter, the heat exchanger or evaporator coil would become dirty and stop working efficiently, causing stress to the system.
Filters are graded on a scale system called a Minimum Efficiency Reporting Value or MERV. The ability to stop particles and expected lifespan are among the criteria used. At the upper end of that scale are fine filtrations used in so-called industrial “clean rooms” and hospitals. Home-filter grading starts near the middle of the scale. Home Depot has its own grading system greatly simplified for customers.
Types of filters. Filters are a necessity, but naturally cause a decrease in air pressure. Thus, a filter must balance the need to clean the air, but not overly suppress air flow. Here are the types available and their retail store prices. You may save a few dollars buying online.
- Fiberglass. This is the most common type of filter. Fiberglass fibers in a flat panel are woven together with a wire grid to reinforce it. They are changed monthly and thrown away. They are the least expensive, starting as low as one dollar each, but are the least efficient filter with ratings of one to four on the MERV scale.
- Pleated. These are made of polyester or cotton fibers and shaped in a pleated form to provide increased airflow, mitigating the drag on air pressure. Being more dense, stopping more particulate matter, they can go longer than a month without changing. With a MERV rating up to 13, these filters start at $14 each for one-inch thickness and go up to $30 for the four-inch thickness.
- HEPA. High Efficiency Particulate Arrestance filters are exceedingly fine, rated up to 20 on the MERV scale and can stop very tiny particles. They are good for people with lots of allergies. It is vital to check with a service professional if your system can handle the size and drag on air flow caused by a HEPA filter.
- Electrostatic. With a MERV rating of four, these filters create a mild electromagnetic charge as particles pass through, causing them to stick to the filter. One drawback: They can create ozone, a gas irritating to the respiratory system. Prices start at $35.
- Washable filters. These filters are permanent. Instead of being replaced, homeowners periodically remove them for cleaning. The filter must be completely dry before reinstalling to avoid mold growth. Washable filters have a MERV rating of about four. Prices start at $30.
Best for the money? Probably the best filter for the money is the pleated filter. It has a midrange MERV rating and can go more than a month without changing.
Diligence pays off. Changing filters on schedule will help prolong the life of a heating and cooling system, saving homeowners thousands of dollars.