Health-related organizations advise cleaning HVAC air ducts when they are full of mold, debris, insects and other impurities. Why does mold grow in air conditioning and heating systems? Is it easy to detect the mold in the HVAC system with so many hidden parts? What are the signs of mold in HVAC air ducts? Do you need professional help to find out if maintenance is needed?


Let’s begin with understanding what is HVAC system and how it works?


Before moving to the question “What are the signs of mold in HVAC air ducts?” let’s discuss what HVAC system is, how it works and why mold accumulates in it.

HVAC stands for heating, ventilation, and air conditioning. HVAC is a combination of machines and systems to regulate air quality and indoor temperature in residential and commercial buildings. In Canada, the HVAC system consumes the largest share of residential energy, but it is also a comfortable and efficient way to maintain indoor temperature. The diagram below shows how the system works in summary; HVAC has its advantage in a way that incorporates fresh air, heats/cools and redistributes air in indoor areas. Making sure that the system is installed correctly and maintained is crucial to achieving the highest level of energy efficiency and indoor air quality.

Main parts of the HVAC system are:

  • Furnace
  • Heat Exchanger
  • Evaporator
  • Thermostat
  • Condensing unit
  • Refrigerant unit
  • Vents
  • Ducts

The furnace is responsible for pushing the air throughout the system. Vents and ducts distribute the air in rooms and other living areas. Before moving to learn what are the signs of mold in HVAC air ducts, let’s see why mold accumulates in HVAC systems at first place.


Why does mold grow in air ducts and HVAC systems in general?


All molds need to grow are humidity and food. Take away these two from buildings, and molds will go. Mold easily accumulates in HVAC systems as all of them are abundant in moisture and food for mold to grow. Moisture is created by air condensation. Air ducts accumulate water if the humidity is high, and not all water evaporates. At the same time, dust and debris enter the system and settle in these water particles. Organic and non-organic particles and humidity help mold grow, travel through the system.

Common parts of the system that is affected by mold are:

  • Air ducts
  • Vents; air vents and intake vents
  • Cooling parts
  • Condensation line (drain pan)

Learn the other reasons of humidity may be present in the system for a long time.


What are the signs of mold in HVAC air ducts?


To recognize when your HVAC system has high level of mold in it and when it needs aid duct cleaning and other maintenance, try to observe the following:

  • See if it is visible in venting filters and air ducts
  • Drip pan is blocked
  • There is a smell o mold: how does mold smell? The smell can be associated with an “old home,” “musty basement,” “humid dust” smells. See how non-organic materials and chemicals can smell.
  • Leaks and puddles around the HVAC system

As there are many parts in the HVAC system that are not visible and in many cases, there is no strong odour; it can be challenging to define if there is mold that should be cleaned or not. In that case, call the professionals.

EPA suggests cleaning the air duct system if:

  • Dirt and debris levels are visibly high
  • Dust enters living area
  • Mold smell is presented
  • Insects are in the system

Prevention and air duct cleaning


After discussing the reasons mold grow and what are the signs of mold in HVAC air ducts, we want to add that the best method of prevention is the professional installation and design of an HVAC system. That will not only prolong the life of filters, ducts and other parts of the system but also prevent mold from growing and improve indoor air quality, which is crucial for health. GoldenLine Green Care tries to share updated information on air duct cleaning to help you maintain your system to prolong its economic lifetime.

Also, read our blog post on how often air ducts should be cleaned.

Ready to Get Started?

Our professional team is ready to start whenever you are. Just click the button below to begin!