HVAC & Climate

How Often Should I Change My AC Filter?

The short answer: Every 30-90 days depending on your filter type, home size, and whether you have pets. In hot climates like Florida where your AC runs 8+ months a year, change it monthly during summer. A 1-inch filter needs changing more often than a 4-inch media filter. When in doubt, pull it out and look — if you can't see light through it, it's done.

Written by Solomon, former HVAC/plumbing field technician with thousands of residential service calls in NW Florida

The Real Answer: It Depends on Your Filter Type

Not all filters are created equal, and the "every 90 days" advice you see everywhere is only half the story.

Filter Type	Thickness	Change Frequency
Fiberglass (cheap blue ones)	1 inch	Every 30 days
Pleated standard	1 inch	Every 30-60 days
Pleated mid-grade (MERV 8-11)	1 inch	Every 60-90 days
Media filter	4-5 inches	Every 6-12 months
HEPA or high-MERV (13+)	Varies	Per manufacturer spec

Field Tip: The cheap $1 fiberglass filters don't actually filter much — they mainly protect the equipment from large debris. If you're using them, change monthly and consider upgrading to a pleated MERV 8-11 filter. It's the best value for most homes.

Factors That Mean You Should Change More Often

Change monthly if any of these apply:

You have pets. Dog and cat hair clogs filters fast. Two or more pets? You might need to check every 3 weeks in peak shedding season.
You live in a hot climate. In Florida, Texas, Arizona, or anywhere your AC runs 12+ hours a day during summer, change monthly May through October.
You have allergies. If anyone in the household has allergies or asthma, a clean filter makes a real difference. Check every 3-4 weeks.
You're doing construction or renovation. Drywall dust, sawdust, and paint fumes will destroy a filter in a week. Change it when the project ends regardless of when you last changed it.
Your home is older. Older homes tend to have more dust infiltration from gaps in the envelope.

What Happens When You Don't Change It

I've pulled filters from systems that looked like felt blankets. Here's what a clogged filter actually does to your system:

Reduced airflow — the blower motor has to work harder to pull air through the clog, using more electricity and generating more heat
Frozen coil — restricted airflow drops the evaporator coil temperature below freezing, and moisture in the air freezes on it. This is the #1 cause of "AC not cooling" calls.
Higher energy bills — a dirty filter can increase energy consumption 5-15%
Shortened system life — the extra strain on the blower motor and compressor accelerates wear. I've seen systems fail 3-4 years early because of chronic filter neglect.
Poor air quality — once the filter is saturated, contaminants pass right through

Cost Context: A $10 filter every month costs $120/year. A blower motor replacement costs $400-$800. An evaporator coil replacement costs $1,000-$2,500. The math is simple.

How to Check Your Filter

Turn off the system (or at least don't change the filter while it's running)
Locate the filter — it's either in a slot on the air handler/furnace, or behind a return air grille on the wall or ceiling
Slide it out and hold it up to a light
If you can see light through it, it's still working. If you can't, replace it.
Note the size printed on the frame (e.g., 16x25x1, 20x20x4) for buying replacements

Pro tip: Buy a 6-pack or 12-pack online. It's cheaper per filter and you'll always have one ready. Set a phone reminder for the first of each month.

Which Filter Should You Buy?

For most homes, a MERV 8-11 pleated filter is the sweet spot. It catches dust, pollen, mold spores, and pet dander without restricting airflow too much.

Avoid going above MERV 13 unless your system is specifically designed for it. High-MERV filters are denser and can restrict airflow on systems not designed for them — causing the same problems as a dirty filter.

Florida Factor: Humidity in NW Florida means mold spores are a constant presence in your air. A MERV 8 or higher filter combined with monthly changes is your best defense against mold growth on the evaporator coil — the most common source of that musty AC smell.

When to Call a Professional

You don't need a professional to change your filter. But if you:

Can't find the filter location
Notice the filter is wet or moldy when you pull it out
See visible mold on the evaporator coil behind the filter
Find that a new filter gets clogged in under two weeks

...then something else is going on. A wet filter means condensation problems. Rapid clogging means either a duct issue or an air quality problem that needs investigation.

This answer covers the basics, but every home is different. Kept's AI Advisor knows your systems — their age, your climate, your maintenance history — and can give you guidance specific to your situation.

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