Mold in HVAC Systems

The System Is Wet By Design

Air conditioning dehumidifies by condensing water out of the air onto a cold evaporator coil. Every operating system therefore has continuously wet surfaces — the coil and the drain pan beneath it.

In Katy, systems run nearly continuously for months and pull enormous volumes of condensate. That is normal. It becomes a problem when the water cannot leave.

How It Goes Wrong

Condensate drain lines clog with biofilm. When they do, the pan holds standing water or overflows. Now there is a permanently wet reservoir with air blowing across it into every room in the house.

Dirty coils compound it. Dust and debris on a wet coil provide the organic material mold needs, turning a clean wet surface into a growth medium.

The Signs

Does Duct Cleaning Help?

Sometimes, and it is frequently oversold. If the source is a wet coil and pan, cleaning the ducts leaves the cause untouched and the smell returns within weeks.

Duct cleaning is genuinely useful when the ducts themselves are contaminated, after construction or a water event, or when growth inside the ductwork is confirmed. It is not a substitute for correcting condensate management.

The Maintenance That Actually Prevents It

Flush the condensate drain line on a schedule — this single item prevents more residential mold in this climate than anything else. Change filters on time and use the correct size so air does not bypass around the filter.

Have the coil inspected and cleaned periodically. Keep the drain pan clear and confirm the secondary pan and float switch function. Annual service that specifically includes the condensate system is worth the cost here.