Lung Institute’s Christine Kingsley Reveals What Could Be Growing in Your Ducts

HVAC Logo IconBy Tom MoorSeptember 13, 2023

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Streptococcus bacteria

Often out of sight and out of mind, your home’s ductwork can unknowingly be a breeding ground for all sorts of unpleasant and unwanted elements, including bacteria and mold. It’s critical to have your ductwork inspected periodically to check its condition especially if you live with people who suffer from allergies, asthma, or other respiratory illnesses.

Unfortunately, bacteria and mold can form over time in compromised air duct systems, creating an unhealthy indoor air supply that can lead to health issues, both minor and severe.

“Eventually, the buildup of bacteria in HVAC systems can pollute indoor air, causing airborne infections and potentially, antibiotic resistance,” said Christine Kingsley, a US Advanced Practice Registered Nurse (APRN) and the Health and Wellness Director of the Lung Institute.

Bacteria Commonly Found in Air Ducts

Kingsley said some of the most common bacterial communities found in air ducts and HVAC systems include:

  • Pseudomonas. Pseudomonas is a diverse genus of bacteria known for its adaptability and can be found in various environments, including soil and water, with some species being pathogenic to plants and animals, including humans. Pseudomonas can cause infections in the lungs, eyes, ears, and gastrointestinal tract.
  • Staphylococcus. Staphylococcus, a genus of bacteria that includes several species, can cause a wide range of infections from minor skin conditions to more severe diseases such as staph infection.
  • Paracoccus. Paracoccus is commonly found in soil and aquatic environments, with certain species playing important roles in nitrogen cycling and bioremediation. If found in air ducts, it can cause several infections including conjunctivitis and peritonitis, as well as bloodstream infection, Kingsley said.
  • Streptococcus. Streptococcus, a genus of bacteria characterized by its spherical shape, is often found in pairs or chains, and includes both harmless species as well as pathogens responsible for a range of infections in humans, such as strep throat and pneumonia.

“Pathogens in air ducts can be dangerous, especially for immunocompromised individuals,” Kingsley said.

Mold Growth in Air Ducts

Although mold is a fungal growth, like bacteria in air ducts, it can also cause dangerous health effects, especially if it’s not removed in a timely fashion.

Mold can form in air ducts when moisture, dust, and organic matter accumulate, providing an ideal environment for mold spores to germinate and grow. HVAC systems are also prone to mold growth if there’s a leak or clog within the condensate drain line, which is responsible for transporting moisture away from a home. If you suspect mold in your air ducts or HVAC system, contact a reputable HVAC company immediately.

Mold, especially large amounts, can quickly cause health symptoms for individuals with allergies and sensitivities.

“Mold in indoor HVAC systems is absolutely dangerous,” Kingsley said. “It can produce respiratory irritants and allergens. It also produces mycotoxins, which is a potentially toxic substance. Inhaling mold spores from HVAC systems can cause plenty of problems, especially in sensitive individuals, ranging from skin rash to pulmonary fibrosis. Molds are especially dangerous to babies, young children, older individuals, people with respiratory and skin problems, and immunocompromised individuals.”

Signs Your Ducts May Be Harboring Harmful Bacteria

Since the condition of ductwork isn’t easily accessible without a professional inspection, it’s difficult to determine whether harmful bacteria or mold are present. It’s important to monitor the health of you and your family members to identify possible signs of bacterial contamination in air ducts.

Below-average indoor air quality can manifest itself in a person’s health. Increased allergy flare-ups, respiratory irritations, and frequent headaches caused by inflamed sinuses are all common signs of compromised ducts. If you notice worsening health symptoms, contact a qualified HVAC professional to inspect your HVAC system and the condition of your ductwork.

How to Prevent Bacteria in Air Ducts

The best route to prevent bacterial and mold growth in ductwork is with regular HVAC maintenance. HVAC systems should be tuned-up and inspected twice a year; once before the cooling season and again before the heating season. Your heating and cooling technician will inspect and clean all necessary components within your HVAC system. Although duct inspections aren’t always part of an HVAC tune-up service, you can ask the technician to perform a visual inspection of the ducts.

If the ductwork is dirty or filled with bacteria or mold, schedule an appointment for a duct cleaning service. Professional air duct cleaners use specialized tools and cleaning products to remove dirt, debris, bacteria, and mold.

Change your HVAC system’s air filters every 2-3 months, or according to the manufacturer’s guidelines, to ensure proper airflow. Also, consider installing a whole-house air purifier or air cleaner to help remove harmful contaminants and pollutants from the air supply. Unlike portable air cleaners, whole-house models provide coverage for the entire house.

“Regular cleaning, sanitizing, and disinfecting of HVAC systems can help eliminate pathogens,” Christine Kingsley said. “Using HEPA filters, especially in households with immunocompromised individuals, in HVAC systems is highly beneficial as this filtration system is proven to have 99.97% efficiency. They can also make use of air purification systems with a hospital-grade MERV 16 filter, aside from carbon filters and germicidal lights.”


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