MERV 13 air filters are designed to last for three months, and experts recommend replacing them regularly to ensure that the air is kept clean, energy costs are reduced, and that the air conditioner is operating properly. However, if the filter is made of fiberglass, it should be changed every 30 days. Pleated filters, which are more expensive, can last up to six months. For good indoor air quality (IAQ), high-MERV filters that are at least two inches thick are recommended.
These filters are more expensive, so changing them every 30 days isn't as cost-effective. A MERV 12 filter such as the Nordic Pure Filter (available on Amazon) is a good option if your oven can handle it. Pleated filters like the Honeywell Ultra Efficiency filter (also available on Amazon) have more square inches of space to trap dust, so they usually require fewer changes - once every 90 days. It's important to note that standard MERV 8-11 filters only block the largest particles of dust and dirt, and don't filter out small bacterial, moldy and fungal particles.
Air filters are usually made of spun fibreglass or pleated paper framed with cardboard for greater stability and rigidity. To check if it's time to change your house's air filter, hang a white sheet several inches from the ventilation grille and see if it turns gray. High-MERV filters with greater thickness usually require only two filter changes per year. HEPA filters are the only type that capture allergens and spores.
If you have young children in your home, you'll need to change your air filter more often - once every two or three months. In general, most air filter manufacturers and HVAC companies recommend changing the air filter every 90 days or three months.