Why Your HVAC Smells Musty – and How to Fix It

Published on December 18, 2025 by: alhhvac

Improve Your Home’s Air Quality With Andy Lewis / Hobson

No homeowner wants to deal with foul odors coming from their HVAC system. Musty smells, in particular, linger through vents and can be hard to get rid of. Usually, they are a sign of an underlying problem that can affect your home’s air quality and system’s performance.

In this guide, the experts at Andy Lewis / Hobson explain the most common reasons for a musty smell in your HVAC system, what you can do about it, and when to call a professional for help.

Common Causes of a Musty HVAC Smell

Musty HVAC smells typically stem from one of several causes. Here are a few common examples:

Dirty Air Filter

A clogged or dirty air filter traps dust, dirt, and moisture. When airflow is restricted, environmental odors get stuck in your system and circulate through your home. Replacing your filter every 1–3 months is one of the simplest ways to keep your home smelling fresh.

Clogged Drain Lines

Your AC creates condensation while cooling the air. That water drains away through a small pipe, but if the line gets clogged, moisture builds up. Stagnant water leads to biological and mildew growth, which often causes musty smells.

Leaky Air Ducts

Air ducts that are cracked or poorly sealed can draw in dust, dirt, or damp air from basements, attics, or crawl spaces. As your system runs, it circulates these odors into your living areas, creating foul smells.

Dirty Evaporator Coil

The evaporator coil cools warm air as it passes through your system. Over time, dust and moisture collect on the coil, creating a perfect environment for biological growth and mildew. A dirty evaporator coil doesn’t just smell bad; it also reduces efficiency and puts extra strain on your system.

Biological Growth

In some cases, the musty odor comes from biological growth inside the HVAC system itself, especially in areas with high humidity. Left untreated, this can impact indoor air quality and aggravate allergy or asthma symptoms.

How to Get Rid of Musty Smells from Your HVAC

Thankfully, getting rid of a musty odor isn’t too difficult. Here’s what we recommend:

• Replace or clean your air filters regularly
• Clear the condensate drain line
• Schedule ductwork inspection and sealing
• Have your evaporator coil professionally cleaned
• Maintain a routine professional HVAC service

That being said, DIY steps can help with small fixes, but if odors persist, it’s best to bring in an HVAC professional to inspect the system thoroughly. Sometimes, the root cause can be too complicated to handle on your own.

How ALH Can Help

At Andy Lewis / Hobson Heating & Air, we’ve been helping Atlanta homeowners solve HVAC issues for more than 50 years. Our licensed technicians can:

• Diagnose the exact cause of a musty odor
• Clean and maintain critical components like coils and drain lines
• Seal ductwork and replace air filters
• Recommend long-term indoor air quality solutions

We offer routine service and expert care that will keep your system running efficiently and your home smelling fresh all year round.

Keep Your Home’s Air Fresh with Andy Lewis / Hobson

A musty HVAC smell is a warning sign that your system needs repairs and cleaning. Andy Lewis / Hobson Heating & Air provides comprehensive HVAC repair and maintenance services that can eliminate even the worst odors. Our professional technicians offer a wide range of services tailored to your specific needs.

You don’t have to deal with bad smells. Don’t wait—contact us today for a free quote!