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How to Prevent Mold in Your HVAC System

Excessive moisture in your home produces a number of problems, such as mold and mildew growth inside your HVAC system and ductwork. Prevent microorganisms from spreading throughout your home when you know how to prevent mold in HVAC systems. We walk you through how to detect mold growth in HVAC and solutions to keep your HVAC system protected.

Causes that Lead to Mold in HVAC Systems

The leading causes behind mold growth inside HVAC equipment are:

  1. Humidity
  2. Condensation
  3. Poor Ventilation


High humidity levels in your home are the biggest cause of mold growth inside the HVAC system as well as inside the house itself. Summer months are usually the time when natural humidity is at its highest, though moisture issues exist in the home year-round. This includes excess humidity caused by showers and baths, washing machines, and other appliances.


While your HVAC units run, your system develops condensation through the air ducts due to moisture within the air. The cooling process also creates a great deal of condensation, as it naturally removes moisture from the air. Normally, this condensation drains away from your home through the condensate drain pan and condensate lines, but if malfunctions or clogs occur, moisture cannot escape and backs up.

Poor Ventilation

If your home is poorly vented, it causes pockets of stagnant moist air to form indoors. Any steam or evaporating water in your air creates more humidity that cannot be circulated out because of poor ventilation. These issues often arise when bathroom exhaust fans and range hoods are not properly used or have malfunctioned.

Indoor Air Quality Solutions for How to Prevent Mold in HVAC Systems

Excess humidity inside a home as well as mold growth are indoor air quality issues. Indoor air quality systems address these issues and provide an affordable solution for how to prevent mold in HVAC equipment as well as mold exposure and growth in the home.

Whole Home Dehumidifiers

Alabama residents battle humidity constantly, which is why a whole home dehumidifier is the best weapon against excessive moisture indoors. Portable dehumidifiers only tackle the humidity in one place, while a whole home unit works directly with your HVAC system to control the moisture throughout your entire house. Notice fewer health issues, such as allergies, asthma and respiratory infections, when a dehumidifier is working alongside your HVAC system.

Ultraviolet Air Cleaners

This indoor air quality product strips your HVAC system of mold before it’s circulated throughout your home. This air cleaner is installed directly within your HVAC system or ducts and uses ultraviolet light energy to neutralize active mold spores so they cannot regrow. Ultraviolet air cleaners also help protect families from bacteria, viruses, and germs, ensuring the air you breathe is pure.

Media Air Cleaners

A media air cleaner traps and eliminates indoor pollutants from your air. They utilize a high efficiency media filter with a long service life, so maintenance is minimal. Media air cleaners with almost any brand of ducted HVAC system can capture up to 99% of particles, depending on the model and filter. Douglas Cooling & Heating offers several different media air cleaners with various features for you to choose from.

Energy Recovery Ventilators

Mold, mildew and dust mites gather in damp, moist areas of your home, and better ventilation prevents moisture accumulation throughout your home. Energy recovery ventilators (ERVs) increase ventilation in your home. They allow stale, contaminated air to vent outdoors while bringing in fresh air. What’s great about this style of ventilation system is that it helps you retain more of your heating and cooling energy to eliminate that waste when stale air is vented outdoors.

How to Prevent Mold in HVAC Systems with Maintenance

Maintenance for your HVAC system doesn’t just help it perform better, it goes a long way toward how to prevent mold in HVAC equipment. These maintenance tips help you prevent mold from taking over your heating and cooling equipment.

  • Schedule seasonal air conditioning preventive maintenance tune ups. With regularly scheduled HVAC maintenance from Douglas Cooling & Heating, our NATE-certified technician keep your system clean, so that it is able to best control the moisture level in your home.
  • Inspect your drip pans and make sure they are cleaned on a regular basis. This prevents condensation buildup and ensures the drainage system is clog-free to prevent mold growth.
  • Use a high efficiency air filter and replace it on a regular basis, as recommended by the manufacturer and your HVAC technician. Filters with a MERV rating of 5 to 13 offer capture of mold spores circulating through your air supply to prevent their spread – the closer to MERV 13 your filter, the better protection you have.

Stop Mold Growth in Your Ducts

Ductwork is typically home to an environment favorable for mold and mildew growth – warm, moist, and dark. Any mold that grows in your ducts can be picked up by circulating air and cycled into your HVAC equipment as well as your living areas.

In addition to indoor air quality solutions that treat humidity levels across the entire home, there are measures homeowners take that address how to prevent mold growth in HVAC ducts:

Insulate Ducts

Ducts run through uninsulated areas of the home, they are affected by the cool air that surrounds them. When circulating warm air from your home comes into contact with cold metal ducts, condensation forms inside the ductwork, just like condensation forms in the cooling process as warm, moist air reaches the cool evaporator coils. This condensation has nowhere to go – there is no drainage system as there is with the evaporator coils, which have the condensation drain pan fitted below. Therefore, it stays in your ducts where it creates an environment for mold growth.

Insulate your air ducts to control the amount of condensation that is produced. Insulation protects your metal ductwork from exposure to cold temperatures in the surrounding areas of your attic, crawl space, or basement where the ductwork runs. This measure helps keep moisture in the air until it reaches the HVAC system and indoor air quality equipment, where it is removed from the air and drained away.

Duct Inspection 

During our inspection, our technicians are also able to identify duct leaks and other malfunctions of the duct system which may be allowing more moisture into the ducts. As the air in the areas where ducts typically run is unconditioned, it usually has a higher humidity level. Air that leaks into the duct system from these areas can deposit moisture that leads to mold issues if unresolved.

It is important to seal duct leaks to stop mold development. Sealing your ducts also keeps conditioned air in, resulting in better comfort and energy savings. The average home loses up to 30 percent of its heating and cooling energy through duct leaks – this service helps prevent that problem.

Duct Cleaning

Have your ducts inspected by a Douglas Cooling & Heating’ HVAC contractor for mold growth. If mold is present, we thoroughly clean and treat your ducts to remove mold growth and help combat recurrence. 

Douglas Cooling & Heating Knows How to Prevent Mold in HVAC Systems

Don’t let mold in your HVAC system or its components affect your family’s health and comfort! Douglas Cooling & Heating offers many solutions to help homeowners manage indoor humidity and moisture levels to prevent mold growth in HVAC systems. Contact us today and work with our NATE-certified HVAC technicians to find the right solution for your home.

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