How often should you change your AC filter in Miami?

Published: 2026-10-11 · Kendall AC Repairs

The filter is the cheapest part of your air conditioner and, at the same time, the one that prevents the most problems. In South Florida, where the AC runs almost all year, changing it on time makes a big difference.

The short answer

In Miami, check the filter every month and replace it every 1 to 3 months. If you have pets, allergies, renovations at home or live near a dusty road, change it monthly.

Thick filters (4 to 5 inches) usually last longer, 6 to 12 months, but only if your system is built for that size.

Signs the filter is dirty

• It looks gray or black when you pull it out.
• Less air comes out of the vents.
• There's more dust on furniture.
• The AC takes longer to cool or the electric bill went up.

What happens if you don't change it

A clogged filter blocks airflow. The indoor coil gets too cold, freezes and, when it melts, water can overflow the drain pan: that's why many leaks start with a dirty filter.

The motor also works harder, the house cools less and electricity use goes up. Over time, it can shorten the life of the unit.

Which filter to buy

Look for the exact size printed on the edge of the old filter (for example 20x25x1). For most homes, a MERV 8 to 11 filter is a good balance between clean air and airflow.

A filter that's too fine (very high MERV) in a system not designed for it can restrict air as much as a dirty one. If in doubt, ask the technician at your next tune-up.

How to change it in 2 minutes

• Turn the AC off at the thermostat.
• Open the return grille or the unit door and remove the old filter.
• Insert the new one with the arrow pointing toward the unit (in the direction of airflow).
• Write the date on the edge with a marker and turn the AC back on.