An HVAC unit's air filter should be changed often. Generally, it is recommended that it should be changed every 3 months. HVAC filters play a significant role in maintaining indoor air quality and energy efficiency. Having a dirty, clogged, or broken air filter will hurt the unit and cause the system to work harder than it should be. According to a 2009 study by the American Society of Heating, Refrigeration and Air Conditioning Engineers, HVAC filters can reduce efficiencies by 10 percent or more. So how do you go about picking the right air filter?

Realize that there are different filters available as well as their minimum efficiency reporting value (MERV; a measure of the effectiveness of the filter). The higher the MERV rating, the better the filter. Here are HVAC filters options you can choose from:

Fiberglass - Thin and flat panels that traps particles from the air. Originally developed to protect your heating and air conditioning equipment, not to improve your indoor air quality. Can be purchased for less than $1 a piece. Removes less than 10% of the air pollutants from your home. MERV rating: 1 - 4.

Pleated - Removes close to 50% of the air pollutants from your home. The number of pleats per foot impacts overall efficiency. Normally costs around $10 a piece. MERV rating: 10 - 13.

Washable - $20 a piece. MERV rating: 1 - 4.

High Efficiency Particulate Arrestance (HEPA) - Most practical air filters for residential systems. Removes up to 85% of air pollutants. MERV rating: 14 - 16. True HEPA filters remove up to 98% of air pollutants from your home; however, only used in whole filtration systems or a standalone purifier.