Every homeowner knows they are supposed to change their air filter. It sounds like a simple task, but putting an air filter in backward—or using the wrong size entirely—can cause severe damage to your heating and cooling equipment.

Before you make a service call for an AC that won't cool or a furnace that keeps shutting off, the very first thing you should do is check your filter. Here is the foolproof, step-by-step guide to changing it correctly.

Step 1: Locate Your Filter

Before you can change it, you have to find it. Depending on how your home was built in Georgia, your air filter will typically be in one of three places:

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Return Air Grilles

In many homes, the filters are located right behind the large return air grates on your walls or ceilings. You may have one large central return in a hallway, or multiple returns in different rooms.

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At the Air Handler / Furnace

If your filters aren't in the walls, look at your indoor unit (in the attic, basement, or closet). There is usually a narrow slot or a covered compartment right where the return ducting meets the actual machine.

Step 2: Turn Off The Power

Never change an air filter while the HVAC system is actively blowing air.

If you remove the filter while the blower motor is running, the system will immediately suck loose dust, pet hair, and debris directly into the mechanical components. This defeats the entire purpose of having a filter. Simply go to your thermostat and switch the system to "OFF" before you begin.

Step 3: Mind the Airflow Arrow

This is the most critical step in the entire process. If you look at the edge of your new cardboard filter, you will see a printed arrow. This arrow indicates the direction that air should flow through the filter.

  • If your filter is at the furnace: The arrow should always point toward the furnace equipment (away from the ductwork).
  • If your filter is in a ceiling or wall return: The arrow should point into the wall or ceiling (in the direction the air is being sucked).

What happens if it's backward? Filters are designed with a specific porous side to catch dirt, and a reinforced side to hold it together. If installed backward, the blower motor has to fight against the reinforced side. This chokes the system and can cause the filter to collapse and get sucked into the fan.

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Step 4: Check the Size & MERV Rating

When you pull the old filter out, look at the dimensions printed on the side (e.g., 20x25x1). You must replace it with the exact same size. If you force a filter that is too large, it will bend and let dirt bypass it. If it is too small, it will rattle and let air slip around the edges.

You also need to choose the right MERV Rating. Do not just grab the highest number on the shelf! A filter with a MERV rating that is too high (like a MERV 13) is incredibly dense and can choke a standard residential AC system. For most homes, a MERV 8 is the perfect balance of catching dust without restricting airflow.

Filter Replacement FAQ

Which direction should the arrow on my air filter point?
The arrow printed on the edge of the air filter should always point TOWARD the furnace or air handler (the direction the air is flowing). If the filter is in a ceiling or wall return grate, the arrow should point UP or IN toward the ductwork.
How often do I need to change my air filter?
For standard 1-inch pleated filters, the rule of thumb is every 60 to 90 days. However, if you have pets, allergies, or run the system fan constantly, you need to change your filter every 30 days.
What happens if I install my air filter backward?
Installing an air filter backward forces the blower motor to pull air against the grain of the filter material. This severely restricts airflow, which can cause your AC coil to freeze, your furnace to overheat, and the filter itself to collapse and get sucked into the blower motor.
Can I wash and reuse a disposable HVAC filter?
No! Unless the filter specifically says "Washable" or "Reusable" (which are usually permanent electrostatic filters), you must throw it away. Washing a standard pleated cardboard filter will ruin the material, cause mold growth, and destroy its filtering ability.