September may signal the beginning of fall, but here in Southern California, our air conditioners don’t necessarily get the memo.

Warm afternoons can continue well into September and October, which means your HVAC system may still be working hard after an already-long summer. That’s why changing your air filter is one of the easiest—and most worthwhile—tasks to put on your September home maintenance checklist.

A dirty filter can restrict airflow, make your system work harder, and contribute to higher energy use. Regular filter changes can also help protect your HVAC equipment and improve indoor air quality.

Why Change Your HVAC Filter in September?

After months of summer AC use, your filter may have collected plenty of dust, pet hair, pollen, and other airborne particles.

When that buildup restricts airflow, your HVAC system has to work harder to move conditioned air throughout your home.

A clean filter can help:

• Maintain proper airflow
• Reduce unnecessary strain on HVAC equipment
• Support energy efficiency
• Improve indoor air quality
• Keep your home more comfortable
• Protect your HVAC system from excessive debris

For Southern California homeowners, September is an especially logical time to check the filter because AC season may be far from finished.

How Often Should You Change an HVAC Air Filter?

There’s no single schedule that’s right for every household.

How often you need a new filter depends on factors such as the filter type, HVAC system, pets, household size, indoor air quality concerns, and how frequently your system runs.

Instead of automatically replacing it every month, check the filter regularly and follow your HVAC and filter manufacturers’ recommendations.

Homes with pets, heavy HVAC use, or more airborne dust may need more frequent changes.

How to Change Your HVAC Air Filter

Changing a filter is usually a straightforward DIY project.

1. Check the Existing Filter Size

Before buying a replacement, look at the dimensions printed on the side of your current filter.

Using the correct size is essential.

2. Turn Off the HVAC System

Turn the system off before removing the old filter.

3. Check the Airflow Direction

Most filters have an arrow showing the correct direction of airflow.

Install the replacement with that arrow pointing in the appropriate direction for your system.

4. Clean Around Vents and Returns

While you’re working on the HVAC system, inspect accessible return-air grilles and vent covers.

Dust, pet hair, and debris can collect around them. Vacuuming accessible buildup can help keep the area cleaner and improve airflow.

Don’t Automatically Choose the Highest MERV Rating

Filter efficiency ratings can be useful, but higher isn’t always better for your particular HVAC system.

A filter that’s too restrictive can reduce airflow if the system wasn’t designed for it.

Check your HVAC manufacturer’s specifications or ask a qualified HVAC professional which filter type and MERV rating are appropriate for your equipment.

When Should You Call an HVAC Professional?

September can also be a convenient time to have your system inspected after a long summer of heavy use.

An HVAC professional can evaluate components that go beyond routine homeowner maintenance, including the thermostat, electrical connections, blower components, and heating equipment where applicable.

The source material for this maintenance tip estimates professional HVAC service at roughly $150 to $500, although actual Southern California pricing can vary considerably depending on the system and services performed.

If your AC has struggled to cool your home, started making unusual noises, produced unusual odors, or caused an unexpected increase in energy use, don’t wait for the season to change before having it checked.

Final Thoughts

Fall may technically be approaching, but Southern California homeowners know September can still feel a lot like summer.

Changing or checking your HVAC air filter is a quick task that can help your system finish AC season more efficiently while preparing your home for the months ahead.

Think of it as a fresh start for your HVAC system after a long Southern California summer.

Frequently Asked Questions

Why should I check my HVAC filter in September?

Southern California can remain warm throughout September and into fall. After months of summer AC use, checking the filter helps ensure accumulated dust and debris aren’t unnecessarily restricting airflow.

How often should I change my HVAC air filter?

It depends on your HVAC system, filter type, pets, indoor environment, and system usage. Check the filter regularly and follow the equipment and filter manufacturers’ recommendations.

Does a dirty air filter make an AC work harder?

A heavily loaded filter can restrict airflow, which may reduce HVAC performance and force the system to work harder to maintain indoor comfort.

Should I use the highest MERV filter available?

Not necessarily. Some high-efficiency filters can restrict airflow in systems that aren’t designed for them. Use a filter compatible with your HVAC manufacturer’s specifications.

When should I call an HVAC professional?

Consider professional service if your system isn’t cooling properly, makes unusual noises or odors, has airflow problems, or needs maintenance beyond routine filter replacement and cleaning.