Have you ever turned on your air conditioner and suddenly felt the presence of a musty, damp odor you hadn’t noticed before? And does that smell disappear when you turn off your HVAC system? This is one of the signs that you may have mold in your air ducts. 

Left untreated, this mold will reduce the indoor air quality in your home, and over time, can cause allergies and sickness for inhabitants, eventually leading to what is called Sick House Syndrome.

But how did that mold get there? And what should you do about it? We’re going to educate you about these aspects of HVAC maintenance in this brief read.

Signs of mold

detecting mold

Here are some telltale signs that will give away the presence of mold and mildew in your air ducts.


In most cases, you will be able to smell the presence of mold before you can see it.

The presence of mold and mildew in the air ducts will make the air smells damp, musty, and stale when your air conditioning is switched on, but will disappear when you turn it off. This should help you narrow down the source of the smell in your ducts.

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The condenser coils in your HVAC system suck in moisture from the air and deposit it in the drip pans. When these get clogged, the drip pans form the perfect environment for mold to grow.

Look for signs of mold around the air conditioner vents and the air ducts as well. However, since mold grows in spores that are invisible to us, the fact that you can see mold in these places is an indication that the outbreak is severe, and that you ought to get a professional to deal with it immediately.


If your family, your pets or you start displaying allergic symptoms every time the air conditioner is turned on, you can be certain that mold in the ducts is the culprit. Symptoms displayed by those infected include itchy eyes, irritated nose, and throat, nausea, and headaches.

If there is considerable mold growth in the ducts and around the AC vents, it is liable to spread through the air and cause these infections.

Read more: How to avoid mold cross contamination

Causes of mold in air ducts

air ducts and mold

Finding out what causes these mold outbreaks is as important as knowing how to detect them and how treat them. A well-known fact is that mold needs a warm and humid environment with poor ventilation to thrive. But let’s find out how our HVAC ducts become infected with it.

An oversized air conditioner

If you’ve bought an air conditioner with a much higher cooling capacity than what the room actually needs, that could promote mold growth.

An oversize air conditioner can cool down a small size really fast, and then turn off before dehumidifying the air. This causes excess moisture to build up in the room as well as in the ductwork, which could lead to mold growth. 

The solution to this problem is to always check with HVAC technicians before investing in an AC unit, just to make sure you’re buying the right capacity for your needs.

Temperature settings

If you like keeping the temperature in the room warmer than usual, you could be promoting mold growth. 

When cool air from the vents meets the warm air in the room, condensation takes place. Moisture forms when the temperature differential is 20 degrees or more. This moisture settles on surfaces and in the vents. Left unnoticed, this moisture can make its way into the ducts, creating the perfect environment for mold and mildew to grow.

Damaged ducts

Damaged and leaking HVAC ducts can also cause a temperature differential, the result of which will be the same as the case above. The cool air in the ducts and the warm air in the walls will create condensation, and in turn, create just the environment mold needs to thrive in.

The way to avoid this is to check your ducts for leaks and clean them periodically. If you do find signs of damage, seal them up at the earliest possible.

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Mold mitigation

air ducts

Getting rid of mold from air ducts may sound like an easy DIY activity, but there are a couple of compelling reasons why you ought to leave this to the experts. 

  1. For one, regular cleaning agents and detergents do not really eradicate mold. While it may look like you’ve cleaned all the mold out, spores tend to stubbornly stick around. These can only be exterminated by experts who know exactly what chemical products to use and how to use them safely.
  2. Not only will professional ductwork cleaners know which growth inhibitors to use in order to get rid of your mold infestation, but they will also know exactly how to handle your HVAC system and the ducts safely. Without the right kind of training, you might end up damaging the system, and that will just lead to more unnecessary expenses.

Professional mold mitigation could cost anywhere between $28.25 and $48.75 per square foot of ductwork. On average, these projects could cost between a low of $500 to upwards of $5,000. Factors that affect the cost include your location, what kind of mold needs removal, and the mold abatement company that you choose to work with.

The best way to deal with mold in air ducts was last modified: August 16th, 2022 by Narayan Shrouthy
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Well, easy to understand, if you want to avoid it, clean regularly, if you already have the problem, ask for professional help…