Considering that a home's HVAC system represents a sizable investment, paying attention to what may be the most important component — the air filter — is worthwhile. Most people do not think about their furnace until something goes wrong, and often that means a repair, which may be both inconvenient and costly. Taking a few minutes to replace the air filter every one to three months (depending on how quickly it gets dirty) can save both money and headaches associated with breakdowns as well as the overall performance of the system.

Why is it important to change the filter regularly?

The main purpose of the air filter is to clean the air that circulates through the heating and cooling system. When the air filter becomes clogged with dust, dirt and debris, the airflow through the system becomes compromised and the furnace has to work harder to achieve the same level of comfort. Over time, an overworked system will no longer function properly and, as dirt gets in, the equipment is more likely to fail. Homeowners may experience cold spots or hot spots in certain rooms, or the equipment will stop working altogether. In addition, an HVAC system that is not properly maintained will need to be replaced sooner.

Another benefit of a clean air filter is improved indoor air quality. Keeping the HVAC system clean will not eliminate all indoor air pollution, however, air filters do prevent excessive dust and dirt from entering the home's ductwork and being deposited throughout the home via the air vents.

Air filters are fairly inexpensive and easy to replace. Doing so is the simplest and most cost-effective way to keep a furnace or air conditioner operating efficiently and saves money in several ways over the life of the system including:

  • lower energy bills due to greater efficiency
  • fewer repairs
  • longer lifespan for the equipment

What type of filter is best?

To start, determine the correct size of the filter by looking at the one currently installed. The size is printed on the cardboard frame, along with an arrow indicating the direction of the airflow. Make a note of both in order to purchase the correct size and to install the new one so that it faces the proper direction.

Check the filter's minimum efficiency reporting value (MERV). MERV ratings range from 1 to 20. The higher the number, the greater the filtration. Consumer Reports found that filters with a MERV greater than 10 tested the best. A filter with MERV that is too high (above 13), however, can block airflow and that can damage a system as well. If greater filtration is needed to reduce indoor air pollution, consider installing an air purifier, rather than compromising the HVAC with a filter that is too restrictive.

Disposable filters are the least expensive and are readily available at home improvement or hardware stores. Some systems can accommodate reusable filters, which need to be washed and thoroughly dried. These are more expensive upfront but can save money over time.

Consult the manufacturer or a certified HVAC technician for more specific questions.