How to Get Rid of Mold in Air Ducts

Mold can grow in just 24 to 48 hours when moisture is present. Getting rid of mold from your air ducts involves removing vent covers and cleaning accessible areas, then replacing your air filter.

Safety hazard: Disturbing mold can spread spores that can affect your breathing. You can handle a small cleanup in two to four hours, but if mold covers more than ten square feet or spreads beyond what you can reach safely, bring in a professional. 

I’ll guide you through each step and share pro tips to help you tackle this job safely and effectively.

Difficulty: Moderate Estimated time to complete: 2 to 4 hours (plus 24 hours drying) Estimated cost:  $50 to $100 (including HEPA filter) When to call a pro: If mold covers more than 10 square feet, is deep, or is beyond reach.

Supplies Needed

Before you start, gather these essential supplies to tackle mold safely and effectively:

Safety Equipment:

• N95 respirator mask (protects from inhaling spores)
• Disposable nitrile gloves (prevent skin contact)
• Safety goggles with sealed sides (shield eyes from mold and chemicals)
• Long-sleeved shirt and pants you can throw away

Tools and Materials:

• Screwdriver (flathead or Phillips, as needed) 
• HEPA filter vacuum (traps mold spores without recirculating them)
• Crevice tool and brush attachments for the vacuum
• Large bucket or tub
• Mild dish soap (for detergent solution)
• Warm water
• Microfiber cloths or soft brushes (won’t damage duct surfaces)
• Spray bottle with clean water (for rinsing)
• Small mirror and flashlight (for inspecting ducts)
• Heavy plastic sheeting to seal off work areas
• Fan or dehumidifier (essential for preventing mold return)
• Large garbage bags for contaminated materials
• New HVAC air filter

Step 1: Turn Off Your HVAC System Completely

First, turn off your heating and cooling at the thermostat. Next, flip the circuit breaker that powers your HVAC to cut electricity completely. This prevents mold spores from spreading throughout your home while you work.

Give the system about 30 minutes to settle so dust and spores drop instead of swirling around. 

Warning: Keep the system off during the entire cleaning process; you don’t want contaminated air blowing around while you’re trying to remove mold.

Pro Tip: Dan Walsh from AAA Home Services suggests a simple smell test before you start: “Turn your system off for 24 hours, then fire it up and immediately smell each vent. Problem ducts hit you with that musty punch within the first 30 seconds of airflow.” 

This quick check helps pinpoint which ducts need the most attention.

Step 2: Inspect and Remove Vent Covers

Inspecting your vents matters because it shows you exactly where mold hides and how far it’s spread. If you skip this, you might miss colonies growing out of sight and wander spores back into your home.

First, put on your N95 (or better) respirator, nitrile gloves, and goggles. Mold spores love to hitch a ride on droplets and dust, so you don’t want to breathe in or touch any residue.

According to Walsh’s advice, here’s what to do next:

• Remove one vent cover at a time. Use your screwdriver to loosen the screws on walls, floors, or ceilings. Keep the screws in a small container so you don’t lose them.
• Place each vent cover in a trash bag to contain dust and spores. Set them aside—you’ll scrub them later with an EPA-approved cleaner.
• Check inside the duct. Shine your flashlight and angle the mirror around the first bend in your ductwork. Mold often appears where moisture collects—like joints and turns.

Warning: If the mold sits within arm’s reach and wipes away with a damp cloth, you can clean it yourself. If it’s deeper, patchy, or slimy, stop and call a professional—tackling hard-to-reach mold without the right equipment can worsen the problem.

Step 3: Prep the Area

Isolate the work zone and vent toward the outdoors to capture most mold particles right where you’re cleaning. That makes your job easier and protects everyone else in the house.

Here’s what to do:

• Choose the room or hallway where you’ll work and move any furniture or belongings at least three feet away from the vents.
• Cover floors and nearby walls with heavy-duty plastic sheeting. Tape the edges securely so nothing can slip underneath.
• Hang plastic sheeting over doorways, leaving just enough space to get in and out. Seal around the frame with tape.
• Turn off ceiling fans and close any registers in that room—this stops spores from circulating.
• Open one window for fresh air, and aim a box fan so it blows directly outside. This creates airflow out of the containment zone without pushing spores into the rest of the house.
• Keep family members and pets out of this area until you finish drying and vacuuming up dust.

Step 4. Clean the Detached Vent Covers

Now that you’ve removed and contained the vent covers, it’s time to wash them thoroughly. This step helps prevent spores from hitching back into your ducts later.

Gather your vent covers, your EPA-approved cleaner, a soft brush, and a bucket of warm water.

Here’s what to do:

• Fill a large bucket with warm water and a squirt of mild dish soap. You want suds but not a bathtub full of bubbles.
• Place each vent cover in the water and let it soak for 5 to 10 minutes. This loosens dust, dirt, and surface mold spores.
• While they’re soaking, grab your soft-bristle brush or an old toothbrush. Scrub each slat and corner gently—avoid stiff brushes that can scratch the metal or plastic.
• Rinse thoroughly with clean water. Run warm water over every inch until the soap and loosened debris wash away.
• Shake off excess water and pat dry with a clean towel. Then set the covers on a dry towel or hang them in the sun or near your fan until they’re bone-dry. Any lingering moisture gives mold a chance to come back.
• Inspect each cover one more time. If you still see fuzzy spots or discoloration, repeat the scrub and rinse until they look and feel clean.

Once the covers are dry, store them in a clean, protected spot until you can move to the next step.

Step 5. Vacuum Accessible Areas with HEPA Equipment

Before you touch anything with a damp cloth, vacuum first. This clears loose dust, spores, and mold fragments so they don’t smear or spread while cleaning. It also helps you see what you’re dealing with and prevents particles from spreading throughout your home.

Sergey Nikolin, president at Product Air Heating and Cooling LLC, warns, “Use a vacuum with a HEPA filter or don’t use a vacuum at all, because a regular vacuum will just blow spores back into the air.”

Here’s what to do:

• Attach the narrow crevice tool or soft brush extension to your hose.
• Insert the hose as far into the duct as you can reach without forcing it.
• Turn on the vacuum and move the nozzle in slow, overlapping strokes from back to front.
• Keep the tool against the duct walls and angle it into corners and bends, holding each position for a few seconds to pull out hidden debris.
• When you finish each duct, empty or replace the vacuum bag or canister outside to prevent rescued spores from re-entering your home.

Note: If you don’t have a specialized HEPA vacuum, you can rent one from many home-improvement stores. You can also buy a suitable HEPA filter attachment for your regular vacuum. If neither of those options works for you, skip to the next step, but we strongly recommend vacuuming first.

Warning: Don’t force the vacuum hose deep into ductwork. You’re only cleaning what’s easily accessible. Anything beyond your arm’s reach requires professional equipment.

Step 6. Apply Mold Cleaner

When it comes to mold in air ducts, simpler is often safer for DIY projects. Rather than reaching for antimicrobial sprays or foggers, start with a gentle detergent solution.

HVAC expert Walsh warns, “Skip the antimicrobial sprays and foggers completely. I’ve seen these create bigger problems by spreading moisture throughout the system without proper drying.” 

Here’s what to do:

• Prepare a mild detergent mix. Combine warm water with a few drops of dish soap in a spray bottle.
• Mist the affected area lightly. Spray just enough so the surface looks damp—this helps trap spores without adding excess moisture.
• Let it sit for 5 minutes. Give the detergent time to loosen the mold so you can remove it more easily.
• Wipe gently. Use a microfiber cloth or soft brush to clean inside the vent and on vent covers. If mold smears or seems deeply embedded, stop and call a pro.

Note: If mold comes off easily, you deal with surface-level growth. If it smears or seems deep, you likely need a pro. Clean only within arm’s reach—professionals use rotary brushes, air whips, and negative-pressure vacuums to get deep into the system.

Step 7: Rinse and Remove Cleaning Residue

Lightly mist the cleaned areas with water (without dish soap) from a spray bottle to remove leftover cleaning solution. Use minimal water—you don’t want to create new moisture problems that could lead to mold regrowth.

Wipe down all surfaces with a clean, damp microfiber cloth.

Step 8: Dry Everything Thoroughly

This step is crucial for preventing mold from coming right back. Use fans or a dehumidifier to dry all cleaned surfaces completely. Allow at least 24 hours of drying time before reassembling anything or restarting your HVAC system.

“Humidity is one of the main Causes of Moldy Ducts, and other things like poor ventilation only make things worse,” explains Nikolin.

Pro Tip: Consider running a dehumidifier in the area for several days if humidity levels are high.

Step 9: Replace HVAC Filter and Reassemble

Install a new, high-efficiency air filter before turning your system back on. The old filter likely contains mold spores and other contaminants you don’t want recirculating through your clean ducts.

If you use a reusable filter, clean it thoroughly according to the manufacturer’s instructions; otherwise, replace it with a new one to ensure effective filtration.

Reinstall vent covers only after everything is completely dry. Turn your HVAC system back on and monitor the area for any return of musty odors or visible mold growth.

Pro Tip: If you want to learn more about filters and find the best type for your home, check out our guide: Washable vs. Disposable HVAC Filters: Which Is Better? 

FAQ About Getting Rid of Mold in Air Ducts

Final Tip: Monitor and Maintain House Humidity

Keep an eye on the cleaned areas over the following weeks. If you notice mold returning quickly, a deeper moisture problem likely needs professional attention.

“If you clean the vents and the area you can reach with a little soapy water and the spots with that musty smell come right back, that’s a pretty clear sign the problem isn’t just on the surface—it’s deeper in the system,” warns Nikolin.

Regular maintenance helps prevent future problems. Change air filters every 1 to 3 months, keep humidity below 50%, and fix leaks promptly. Professional duct inspections every 3 to 5 years catch issues early.

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Read More:

• How to Get Rid of Mold on Walls
• How to Get Rid of Black Mold
• Signs of Mold in Your Home
• Health Risks of Mold in Your Home

Main Image: Air vent with mold and stains. Image Credit: Eakrin / Adobe Stock