Why Does Mold Easily Grow on My Air Vents?

October 20, 2016

In most cases, mold grows on your air vents because you probably have mold growing elsewhere in your home. And that’s probably happening due to one of two things:

  • Humid air is leaking into your home
  • Your home has poor ventilation

To help you understand why these two things can lead to mold growth, you need to know why mold grows in the first place.

Why mold grows in your home

The fact of the matter is that mold is inevitable, mostly because it is a part of the natural environment.

Mold thrives when met with a perfect storm of :

  • Mold spores
  • Moisture
  • A food source (like dust, wood, paper, and drywall)

There will always be mold spores somewhere in your home. And there will always be a “food source”. So, that means one thing: You need to control moisture/humidity levels of your home.

Mold grows when the relative humidity level in your home rises above 50%.

So, what would cause humidity to get that high in your home? The cause could be dependent on the age of your home.

Causes of high humidity in your home

For older home's: Air leaks

Old homes are not very airtight. This means outdoor air can easily leak inside, mixing with the cool air and condensing into water droplets on windows, walls, or other surfaces. This condensation increase humidity levels and therefore gives mold spores the moisture they need to grow.

For newer homes: Too airtight

Newer homes have the opposite problem; they are too airtight and don’t get enough fresh air to get rid of stale, humid air inside. Good ventilation will help regulate temperature and humidity levels in your home.

So, what can you do about these problems?

Methods for controlling humidity levels in your house

For newer homes: Update your ventilation system

Consider installing a central-fan-integrated supply ventilation system which allows for better fresh air distribution by drawing outside air into the system before redistributing this clean air throughout the house.

Heat-recovery ventilators and energy-recovery ventilators with a dedicated duct system are a less expensive option and can be just as effective. These systems transfer heat energy in the winter and cooling energy in the summer into your home in the form of fresh air via recycled air flow.

The benefit is improved indoor air quality, so you can prevent the buildup of humidity. The best part is that by recycling the air, these systems reduce wasted energy, which saves you money.

However, if you have an older house, where leaks and gaps can occur in the walls or in the roof over time, there is always the chance that moist air could get in through these openings.

In this case, a different type of fix is needed.

The first step is to determine whether or not you can install one of these updated ventilation systems in your home. Heat-recovery systems can do wonders to improve the ventilation as they would in a new house.

You could also consider an individual room ventilator which also works to eliminate stale and dangerous air and replace it with fresh and filtered air from the outdoors.

For older homes: Fix those excess leaks

Of course, if your home contains too many leaks and holes, a new ventilation system can only do so much.  To fix a leaky home you first need to know where leaks can happen.

Finding and fixing air leaks can be time consuming, so we recommend you hire a professional  to do it for you.

Other humidity control tips

  • If you have rooms in your home where you know the humidity is higher, like kitchens, bathrooms and laundry rooms, you might consider placing a dehumidifier there. These machines essentially extract water from the air and replace it with cleaner, less moist air.
  • You may also consider checking your pipes for leaks, especially in older houses. Often times these pipes can be a primary source of condensation. Have a professional come in to assist.
  • In the warmer months, set your air conditioning to a dry setting. In this mode, the fan runs at low speed and the compressor is on for short duration in large cycles. This allows the AC to run longer and therefore remove more humidity.

Bonus: Catch mold spores mid-air

While you can’t rid your home of all mold spores, you can catch a lot of the airborne ones.


By Installing a whole-house filtration system that has MERV 11 grade filters These filters can catch mold spores (and other small airborne particles) as they enter your ductwork

Keep your home comfortable and sickness free with Advanced Air

At  Advanced Air, we can help you choose the filtration systems that are perfect for your home, and we can contribute to making your home free of sickness without breaking the bank.

Call us at 888-853-5143 to learn more about how our air quality systems can work for you.