Can Your Air Conditioning System Develop Mould Growth Inside?

There is one common thing people know about moulds: They grow in a cold and moist environment. Since your air conditioning unit fits that description perfectly, does that mean moulds could grow inside? If you are curious to know if that is possible, how it can happen, and how you can prevent it, this article will tell you all the essential details. 

Why Mould Thrives in Cold Temperature

Fungi grow at different temperature ranges, but most of them thrive in temperatures between 15.5° and 26.6° Celsius, which is also ideal for humans. They grow fast, especially if the air is humid or if they are in damp conditions. 

How It Happens

Air conditioning units in homes are often used during the summer season when the air is humid. When the AC unit is running, cold air runs through its warm ducts. When that occurs, vapour starts to develop in the ductwork. 

Alternatively, when the unit is not in use, water droplets start to accumulate in the ducts. This water does not evaporate immediately. Instead, it runs inside the system and becomes warmer. That makes a perfect place for mould growth. 

Furthermore, when other particles such as dust, pollen, skin particles go inside the unit, they trigger mould infestation inside your AC system

How to Know If Your HVAC System Has a Mould Infestation

Here are some signs that could help you determine if there is mould developing in your HVAC system:

  • Musty Smell: You start to notice a mouldy and stale smell coming near the air vents of your home.
  • Increasing Odour: As soon as you run your AC unit, you immediately notice a distinct smell intensifying.
  • Presence of Black Fungi: One visual symptom is patches of black fungi surrounding different elements of your AC system, such as the vent, drip pans, evaporator coil, etc. 
  • Health Problems: Your family members are starting to get irritations in their throat, nose, eyes, or sinus passages, especially when the system is running.

Those are some of the signs you could observe inside your home, but you should have your system checked by HVAC professionals to determine its actual condition. These signs are usually unnoticeable or only appear when the situation has worsened. That is why regular maintenance and checking are important to notice the early signs and prevent potential problems. 

Effects of Mould in the AC System

Mould may seem like a tiny problem, but it can damage your home and risk the health of all people living inside it. The microscopic spores can spread through the house, causing moulds to grow in other parts. Breathing them in could also trigger or lead to respiratory problems, rashes, fatigue, nausea, and dizziness. For people who are sensitive to moulds or have allergies, mould spores could be life-threatening.

How to Prevent It

Fortunately, there are small things you can do to prevent it from occurring:

  • Regularly replace your HVAC filter. Do not let it become too dirty. If you can, find a filter specially designed for mould control and install it in your system.
  • Utilize a UV light air purifying system and install it in your HVAC system.
  • Seal your air ducts to prevent condensation from occurring inside. 
  • Regularly empty the water from the drip pan.
  • Clean the drip pan with bleach to kill off any developing mould. 
  • Use a dehumidifier to balance things inside a home. 


Keep these preventative measures in mind, especially if you live in an area with high humidity. In case mould is already present inside your system, avoid taking matters into your own hands. Instead, immediately call a professional. Cleaning an AC unit and purging an entire HVAC system of mould are two different things. The latter requires more intensive cleaning, including removal of various components, which only professionals should conduct.

If you have concerns about mould in your HVAC system in Edmonton, call us at Legacy Heating. We specialize in HVAC maintenance and can eliminate your mould problems through HVAC cleaning and tune-ups. Call us at 780-900-1109 to book a service. 

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