Mold in Air Handler: Causes and Solutions

If you have mold in your air handler, you need to take action now to protect your health, indoor air quality (IAQ), and HVAC system.

There are a few signs of mold in your air handler and ductwork, including:

• Visible mold growth
• Musty odor at the air vents when the HVAC system is running
• Increased allergy symptoms with no obvious cause

Multiple issues can cause mold growth in your HVAC system, including:

• High humidity
• Clogged air filter
• Clogged condensate drain line or drain pan
• Leaky air ducts
• Improperly sized AC or heat pump

First, we’ll go over what to do if you have mold in your residential HVAC system and then how to prevent it once everything is disinfected.

The solution to fix the problem will depend partly on what caused it. If you discover mold at your air handler unit, on the filter, or in the air vents, turn the system off to prevent mold spores from circulating throughout your home.

Contact your HVAC company to evaluate the problem. Removing mold from your HVAC system is a job for professionals. Some HVAC companies offer air duct cleaning services. If yours doesn’t, ask for a recommendation. You need to decontaminate your air handler and likely your ductwork system.

Make sure that the company you hire is a member of the National Air Duct Cleaners Association (NADCA).  NADCA members clean more than just ductwork. They’ll inspect and clean the entire system, including

• air ducts and air vents
• evaporator coil
• condensate drain line
• drain pans
• registers
• grilles
• air plenum
• blower motor and assembly

It’s important to know what caused the mold in your HVAC system because if you don’t solve the root cause, the mold problem will return.

Remember the causes? Here they are again, with the appropriate solution. Controlling moisture is key.

• High humidity
• Clogged filters
• Clogged condensate drain line or drain pan
• Leaky air ducts
• Improperly sized AC or heat pump

If you live in a humid area, consider a whole-home dehumidifier to help keep humidity levels within safe limits. You can also ask your HVAC professional about UV lights for HVAC. These can be coil-sanitizing lights that are placed by the evaporator coil or air-sanitizing lights placed in your ductwork.

Clogged air filters can start to retain moisture, providing a breeding ground for mold. Get in the habit of changing your filter every 1-3 months, depending on the quality of the filter. Get some tips in our HVAC air filter maintenance guide.

During regular HVAC maintenance, an HVAC technician inspects your system inside and out. Among many other tasks, they inspect and clean the drain line and drain pan as needed. We suggest maintenance every fall and every spring to spot problems while they’re still small.

Tell your HVAC company about any airflow issues you’re experiencing. They can help determine if leaky HVAC ducts are a problem and offer ductwork sealing or ductwork replacement, depending upon the severity of the issue.

An AC unit or heat pump that’s too big or too small can cause humidity problems. That’s because while the unit cools, it also removes humidity from the air. An oversized unit can quickly cool your home but fail to properly dehumidify. Talk with an HVAC professional about proper sizing.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

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