How to Clean or Replace an AC Filter at Home

Keeping your AC filter clean is one of the simplest ways to improve indoor air quality, protect your equipment, and reduce energy bills. A clean filter supports healthy airflow and helps your system trap dust, pollen, and smoke particles—critical in Southern California’s wildfire seasons. Below is a safe, step‑by‑step guide to identify your filter type, clean or replace it correctly, and avoid common mistakes that can damage equipment or void warranties.

#1 AC Guys is a fourth‑generation family of engineers with 80+ years in engineering, serving homes and businesses across Los Angeles County and nearby areas including Orange County, Ventura County, and Western Riverside County. Our mission is healthy air at home for a healthy life. We specialize in large and complex residential and commercial projects, and our engineers trained at the factory with Fujitsu (Japan), Mitsubishi Elektrik (Thailand), Midea (China), Gree (China), and Hier (China).

Identify your AC filter type

• Ducted central AC or furnace/air handler: Usually has a rectangular disposable filter (1–4 inches thick) at the return grille or inside the air handler.
• Ductless mini‑split: Typically has one or two washable mesh screens behind the indoor panel.
• Window or portable AC: Often includes a washable mesh filter behind the front grille.

Note: If your system has multiple returns, there may be more than one filter. Never operate the unit without a filter.

What you’ll need

• Thermostat access to turn the system off
• Flashlight
• Measuring tape and phone to record size
• Disposable replacement filter (correct size and MERV rating) or mild dish soap for washable filters
• Vacuum with soft brush and a microfiber cloth
• Gloves and a stable step stool if needed

How to replace a central AC/furnace filter (disposable)

1. Turn the system off at the thermostat. This prevents debris from being drawn in and protects the blower.
2. Locate the filter. Check the large return grille(s) on walls/ceilings or the air handler/furnace cabinet. Open the grille or panel carefully.
3. Check size and airflow arrow. Typical sizes look like 16x25x1 or 20x20x1. Note the size and the arrow direction on the old filter.
4. Remove and inspect. If the filter looks gray, clogged, or the pleats are coated in dust, it’s time to replace.
5. Select the right MERV. For most homes, MERV 8–11 balances capture and airflow. For finer particles (e.g., wildfire smoke), many homeowners choose up to MERV 13 if the system supports it.
6. Install the new filter with the airflow arrow pointing toward the blower (usually toward the air handler/furnace, away from the return grille).
7. Close the panel or grille, turn the system back on, and write the install date on the filter or in your phone.

Tip: If your system uses a thicker media filter (2–4 inches), replacement intervals are usually longer but follow the manufacturer’s guidance.

How to clean a ductless mini‑split filter (washable)

1. Power down. Turn the unit off and allow the fan to stop. For extra safety, switch the dedicated breaker off.
2. Open the front panel. Gently lift until it clicks. Slide out the mesh screen(s) and any prefilters.
3. Vacuum dust off the mesh with a soft brush. Rinse with lukewarm water. Use a small amount of mild dish soap for stubborn dirt; avoid harsh chemicals.
4. Dry completely. Lay the filter flat to air‑dry fully. Do not use heat or reinstall while damp.
5. Wipe the cabinet’s dust with a dry microfiber cloth. Do not touch the coil fins or spray chemicals inside the unit—this can damage coatings and affect warranties.
6. Reinstall the dry filters, close the panel, restore power, and set a reminder to clean monthly in heavy‑use or dusty seasons.

How to clean a window or portable AC filter (washable)

1. Unplug the unit. Safety first.
2. Open the front grille and remove the mesh filter.
3. Vacuum loose debris, then rinse. Use mild soap if needed, and rinse thoroughly.
4. Let the filter dry completely before reinstalling to prevent mold or odor.
5. Reinstall, close the grille, and plug the unit back in.

How often should you change or clean your filter?

• 1‑inch disposable filters: every 1–3 months
• 2–4 inch media filters: every 3–6 months (some up to 9–12 months—check the label)
• Mini‑split washable screens: inspect monthly; clean as needed
• Window/portable AC filters: inspect monthly

Adjust frequency if you have pets, allergy/asthma concerns, recent renovations, or during wildfire events. If you notice dust build‑up near returns, reduced airflow, longer cooling cycles, iced refrigerant lines, or a whistling return grille, check the filter first.

Choosing the right MERV rating

MERV 8–11 works for most households, catching common dust and pollen with minimal airflow penalty. MERV 13 can capture finer particles and some smoke, but it increases resistance. If your blower or ductwork is marginal, a too‑high MERV may reduce airflow, increase energy use, or cause icing. Consult your system manual or a qualified specialist before switching to higher‑MERV filters.

Common mistakes to avoid

• Wrong size: A filter that’s too small lets air and dust bypass; too large won’t seat properly.
• Backwards installation: Always match the airflow arrow toward the blower.
• Over‑dirty or wet filters: Running with a clogged or damp filter risks mold growth and compressor strain.
• Stacking filters or using add‑on cut‑to‑fit layers: This can spike static pressure and harm the blower.
• Assuming the filter solves all air quality issues: Severe odors, VOCs, or biological growth need specialized solutions.

Safety, warranty, and insurance notes

Homeowners can usually handle filter maintenance safely. However, if the filter access is near high‑voltage compartments, if you see ice on lines, unusual noises, burning smells, or persistent airflow issues after replacing the filter, stop and leave the panel closed. Many equipment warranties and some insurance policies require that diagnosis, repairs, and system modifications be performed by qualified specialists, and documented maintenance may be requested during claims.

Why this matters for Southern California homes and businesses

Our region’s mix of heat waves, coastal humidity, dust, and wildfire smoke makes proper filtration critical. In Los Angeles County and nearby areas including Orange County, Ventura County, and Western Riverside County—from Los Angeles, Pasadena, Santa Monica, Glendale, and Long Beach to Anaheim, Irvine, Santa Ana, Costa Mesa, Ventura, Oxnard, Thousand Oaks, Riverside, Corona, and Temecula—regular filter care supports comfort, energy efficiency, and healthier breathing day‑to‑day.

About the #1 AC Guys difference

#1 AC Guys is a family business in Southern California with 80+ years in engineering across four generations. Our mission is healthy air at home for a healthy life. We handle residential and commercial systems, including large and complex projects. Our engineers trained at the factory with Fujitsu (Japan), Mitsubishi Elektrik (Thailand), Midea (China), Gree (China), and Hier (China), bringing manufacturer‑level insight to filtration choices, airflow, and system performance. If your system presents recurring filter‑related issues, unusual static pressure readings, or you’re considering higher‑MERV upgrades, expert evaluation is the safest path forward—especially where warranty or insurance requirements apply.

Set a calendar reminder today, check your filter, and breathe easier all season.