Mold in Air Ducts: Signs, Causes and What to Do in San Antonio
The warning signs, why humid Texas summers cause it, and why fixing the moisture matters as much as the cleaning.
Mold in air ducts is one of the more worrying things a homeowner can smell. The good news is that the cause is usually easy to find, because mold needs moisture, and in an air conditioning system moisture only collects in a few places.
What are the signs of mold in air ducts?
- A musty smell when the AC turns on that fades after the system has run for a while.
- Dark spots on vent covers or on the ceiling right around a register.
- Allergy-like symptoms that are worse indoors and ease when you leave the house.
- Visible growth on the cooling coil or in the drain pan inside the air handler.
Dark dust on a vent cover is not always mold. Often it is ordinary dust stuck to condensation. A camera inspection is the quickest way to tell the difference without tearing anything open.
Why do San Antonio homes get mold in ducts?
Our summers are long, hot and humid, and the AC pulls a lot of water out of the air. That water is supposed to drip off the coil into a drain pan and out of the house. Problems start when it does not:
- The coil stays wet for months. A damp, dark coil is an easy place for growth to start.
- The drain line clogs. Standing water in the pan feeds mold right next to the blower.
- Ducts sweat in the attic. Cold ducts in a 130-degree attic collect condensation, especially if the insulation around them is torn or a joint leaks.
- The system is oversized. An AC that cools quickly and shuts off does not run long enough to dry the air.
What should you not do?
Do not spray bleach or household cleaners into your vents. They do not reach the source, they can damage flex duct, and the fumes go straight into the rooms you live in. Do not ignore it either, and do not pay for a "treatment" from a company that will not show you photos of what they found.
What to do about mold in air ducts
- Confirm it. Get a camera inspection, and if you are unsure whether it is mold, a lab test of a sample will settle it.
- Fix the moisture. Clear the drain line, repair leaking or sweating ducts, and have the system checked. The EPA's advice on duct cleaning is clear on this point: if the moisture problem is not corrected, the growth comes back.
- Clean the system. A full cleaning under negative air pressure removes the debris that holds moisture and spores.
- Keep the coil cleaner. A UV light aimed at the coil helps limit regrowth on the one surface that stays wet all summer.
If what we find on camera is more than a duct cleaning can fix, we will say so before any work starts.
Related reading and services
See air duct cleaning and UV light installation, read whether duct cleaning is worth it, or check the current coupons.
Mold in air ducts
How do I know if I have mold in my air ducts?
The most common sign is a musty smell when the AC turns on. Dark spots around vents and worse allergy symptoms indoors are others. A camera inspection confirms what is actually there.
Is mold in air ducts dangerous?
Mold can irritate allergies and asthma, so it should not be ignored. If anyone at home has health concerns, talk to your doctor and get the source fixed quickly.
Can duct cleaning remove mold?
Cleaning removes growth and debris from the ducts, but it only lasts if the moisture source, such as a clogged drain or sweating duct, is fixed as well.
Why does my AC smell musty?
Usually because the cooling coil or drain pan stays wet and something is growing on it. Clearing the drain and cleaning the system typically fixes it.
Do UV lights kill mold in ducts?
A UV light aimed at the coil helps limit growth on the coil and drain pan. It does not clean the ductwork itself, so it works best after a cleaning.
