Both heating and cooling can cause mold growth, but cooling is the number one cause of microbial growth due to condensation. When air conditioning cools the air, it also removes the moisture (humidity) that’s constantly coming back to the system from the home, via the return air ducts. This condensation can rest on evaporative coils, pool in condensation pans, ductwork, or on the filter, creating a perfect environment for mold. 

Though HVAC heating can create mold growth, it is far less likely if the system is properly maintained. 

HVAC system maintenance: 

For forced air HVAC systems in any climate region, the following considerations are key for preventing microbial growth

Filter Changes – changing the filter once a month is a labor of love to your home and health. It can be a pain and so easy to skip. I have the same feelings and it’s what I do for a living. In case you missed it above, your home needs to BREATHE  and that is the number one priority if you have mitigated active mold growth. This is best accomplished by allowing your HVAC to breathe and your ERV/HRV system to work properly. Which is to say – change the filter regularly! 

Coil Cleaning – Cleaning the evaporative coils in your HVAC system regularly (once per year) will help to prevent mold and bacteria build up. 

Duct Cleaning – A word on ducting – if you don’t already have ducting, but are considering adding it to your home, insist on hard pipe ducts. Never use flex pipe.  Flex pipe contains small ridges, which can harbor mold when condensation from higher humidity is present. Additionally, it’s much, much easier to clean a smooth sided duct. How hard would it be to clean this? You can see over time that the foil on the interior has eroded, exposing the insulation. A perfect haven for condensation mold growth that you can’t access to replace. You don’t even know that mold growth is occurring in these instances. 

Versus this:

Onto Cleaning – hire a reputable company that knows how to clean ductwork properly. Every person I’ve ever met with mold illness has also been highly sensitive to most things in their environment. This means absolutely no cleaning chemicals can be used unless you are mitigating your home and aren’t living in the house for an extended period of time. Instead, mechanical cleaning in the form of brushes, agitation, along with effective vacuuming, are the course. 

Condensation Pan Inspection and Cleaning – Especially in humid climates, your HVAC system is creating enormous amounts of condensation moisture. This is collected and discharged via pipe either to the exterior of the home or into the drainage systems of the home. If this is clogged due to debris, dust, bacteria, etc., the water cannot be discharged, and the condensation pan will fill quickly and then overflow and create a water damage scenario. The condensation pan should be cleaned once a year.