Musty smells from your HVAC system usually indicate moisture buildup or a dirty component that’s been ignored for too long. The good news is that you can remove that smell by applying the right methods. Start by replacing air filters and making sure your drain pan is clean. Clear out the drain lines and clean the evaporator coils properly.
If mold is hiding in ductwork, try to remove it immediately. Lower the indoor humidity levels. Moreover, install UV lights inside your HVAC to stop microbial growth, and run the fan for a short while after every use to help dry things out. When done together, these actions eliminate the smell and help your entire heating and air system run cleaner and more efficiently.
Easy Ways to Eliminate Musty Smells From HVAC Units
Musty odors form in different parts of your system where moisture and dirt gather. Here’s how to address the root of the problem.
1. Replace Air Filters
Start with your air filters. Air filters clogged with dust, moisture, and organic particles become the perfect breeding ground for mold. Every time your system runs, it pushes that air and that smell through your house.
Change your filters every 30 to 90 days, depending on use. If you live in a humid climate or have pets, stick closer to the 30-day mark. A clean filter stops mold from entering the system in the first place.
2. Clean the Drain Pan
Check the drain pan underneath the evaporator coil, where moisture collects as your AC pulls humidity out of the air. It will start smelling if that pan holds water, even just a little.
Turn off the unit and look inside. If you see grime or standing water, clean it with white vinegar and water and dry it thoroughly. This simple step prevents mold at one of its most common starting points.
3. Clear Drain Lines
Your condensate drain line carries water from the drain pan out of your home. If it’s partially clogged, water sits in the line and eventually smells bad. Worse, it can back up and spill over into your system.
Pour a 50/50 mix of warm water and white vinegar into the drain line opening near the indoor unit. Do this every month or two. You can also vacuum the outside end of the line using a shop vac to pull out deeper blockages.
4. Clean Evaporator Coils
Evaporator coils cool the air and create condensation. If the coils are covered in dust or grime, that moisture sticks and creates the perfect home for mildew and mold. That’s where many musty smells begin.
Turn off the power to your HVAC unit and open the access panel. Use a no-rinse coil cleaner spray or a soft brush to remove any visible buildup. A clean coil smells better and cools more efficiently.
5. Remove Mold in Ductwork
When the smell keeps coming back no matter how much you clean, there’s a good chance mold is hiding inside the ducts. That’s where air passes through and picks up odor before it hits your vents.
Look at the grilles and registers. If you see black or green spots around them, it’s time to act. You’ll need a professional to clean the ducts fully because surface cleaning won’t reach the deeper areas where spores live.
Read More: Why Your AC Is Blowing Warm Air—and How to Fix It
6. Minimize the Indoor Humidity
High humidity is an ideal environment for mold to grow. By bringing their levels down, you can stop the odor from forming in the first place.
Use a dehumidifier in damp rooms. Keep bathroom exhaust fans running during and after showers. Seal leaky windows and fix any plumbing problems that contribute to moisture buildup. Your target is 40 to 50 percent indoor humidity in the safe zone.
7. Install UV Lights
Install UV lights to kill microbes at the source, like the evaporator coil or inside the air handler. This can prevent mold and bacteria from forming inside your system.
Once installed, they run constantly and silently. You won’t need to think about them, but you’ll notice the difference in air quality. It’s a solid long-term move if you want to eliminate the smell permanently.
8. Run Fan After Use
Every time your AC turns off, moisture lingers inside the system. If it just sits there, it becomes a mildew breeding ground. But if you let the fan run for a little while after the cooling cycle, it dries everything out.
You can do this manually or adjust your thermostat settings to keep the fan running for 10 to 15 minutes after each use. That extra airflow clears out the moisture before mold can form.
Signs Your HVAC System Needs Immediate Attention for Odor Issues
If you’ve already handled maintenance and the odor remains, something more serious may happen inside your system. Pay attention to these signs that demand quick action:
- Persistent Musty Smell After Cleaning: The smell keeps returning even after replacing filters and clearing drains.
- Poor Airflow or Cooling: Weak output often means internal buildup or a clogged coil.
- Mold Growth Around Vents: Visible mold around grilles usually means deeper mold in the ducts.
- Moisture Build-up in Ductwork: Condensation around ducts means your humidity levels are too high or there’s poor ventilation.
- Increased Energy Bills: If your system works harder due to internal mold or dirt, your power bill will reflect this quickly.
Read More: What to Expect During a Routine AC Maintenance Visit
Conclusion
Musty odors in HVAC systems result from moisture, mold, and dust collecting in the wrong places. You can remove the smell by taking direct, practical steps such as cleaning the filters, clearing out drain lines, scrubbing the coils, removing duct mold, cutting humidity, and letting your system dry fully between uses. Adding UV lights keeps bacteria from forming in the first place.
If you’ve done all this and the smell returns, your heating and air system likely has a deeper issue that needs a professional to inspect. Either way, don’t ignore it because clean air is a fixable problem when you go after the cause, not just the smell.
