While mold won't usually grow in your HVAC system, there are certain circumstances under which it can. If and when it does, it's important to locate it and discover what's causing it. Once this is figured out, you can have it safely removed and prevent it from coming back.


One of the most common places where mold will show up is inside your ducts. Typically, ducts don't provide a good environment for mold to grow. If dust and debris start to build up on the inside, and especially if the inside of your ducts gets too moist, this can make it much easier for mold to grow. This likelihood can also be increased if there are many gaps in your ducts that make it easier for dust and mold spores to get inside.

Near the Condensate Drain

When moisture is pulled out of the air during the cooling process, it's collected in the condensate drain where it is directed outside of your house. If this drain is clogged, that moisture can instead start to back up into your air conditioning unit. When the pan overflows, water can dampen the surrounding area, which can promote mold growth. In some cases, your air conditioner may shut off early if the pan starts to get too full, but if it doesn't, it will keep running even as moisture continues to back up into your home.

Near the Evaporator Coils

The evaporator coils help facilitate the cooling process. In certain situations, the coils can freeze up completely, and when they thaw, this can result in enough moisture to flood the drain pan. When this happens, it can have the same effect as a backed-up condensate drain.

The evaporator coils can freeze up when there isn't enough airflow, such as when your air filter gets too dirty, if the coils become too dirty, or if you're running low on refrigerant. These usually aren't serious and can be repaired by a professional, but if left alone too long, the potential flood of moisture can create a serious mold risk.

Have it Cleaned

If you do have mold growing in your HVAC system, it needs to be dealt with right away. Because your air conditioner spreads air all over your house, it can do the same with mold spores if they are present.

If mold growth is isolated, you can often take care of it on your own using things like bleach, vinegar, and hydrogen peroxide. If growth is more widespread, and especially if it's in your ducts, professional cleaning is a better option. With the growth in ducts, in particular, it's not just important to remove the mold itself; it's also important to clear out any dust and debris and seal up any holes or gaps that led to this mold growth, to begin with.

On top of mold removal, talk to an HVAC specialist about what allowed the growth to begin with and discuss what you can do to prevent this problem from happening again in the future. This can include everything from changing your air filter more regularly to taking measures to combat excessive moisture, so it helps to have professional input tailored to your situation.