When this homeowner off Andorra Point Trace in Richmond called us, the complaint was simple: the house smelled musty every time the AC came on, and it wasn’t going away no matter how often they changed the filter. That’s a call we get a lot in the summer here, and it almost always points to the same place. Not the filter. Not the thermostat. The ductwork.
We pulled the supply registers to take a look, and the photos tell the story better than we can. The vent louvers were coated in mold. The fiberglass duct board inside the plenum had mold growth and pitting across the liner. This wasn’t a light dusting of debris. This was active microbial growth living in the part of the system that touches every breath of air moving through that home.
Why Mold Shows Up in Houston-Area Ductwork
Mold needs three things to grow: moisture, a food source, and time. Air conditioning systems in our climate hand it all three.
The moisture comes from the cooling process itself. When warm, humid air passes over a cold evaporator coil, water condenses out of it. That’s how your AC dehumidifies the house. But it also means the coil and the duct board right around it stay damp for most of the cooling season, which in the Richmond and greater Houston area runs the better part of the year.
The food source is dust. Every system pulls in airborne particles, and some of them settle on the duct walls and the register vanes. Dust is organic. To mold, it’s a meal.
And time is the one nobody thinks about. A duct system that hasn’t been cleaned in five, eight, ten years has had every summer to let that cycle repeat. The growth doesn’t happen overnight, which is exactly why most people never catch it until the smell gets bad enough to notice or someone finally pulls a register off the wall.
Mold on the supply register louvers — the visible edge of the problem.
The register pulled from the wall, caked in mold and dust.
What We Actually Found at This Richmond Home
The registers were the obvious part. When you can see mold speckled across the louvers of a supply vent, you already know the air passing through them isn’t clean. But registers are just the visible edge of the problem. The real concern was further in.
Inside the plenum, the duct board liner was cracked and pitted, with mold worked into the fiberglass itself. That matters because duct board is porous. Once mold takes hold in it, wiping the surface doesn’t solve anything. The growth is in the material, not just on it. A proper cleaning has to address the full system, and in cases where the board is too far gone, sections need to be replaced rather than just cleaned.
Mold worked into the fiberglass duct board inside the plenum.
The plenum interior — mold and pitting across the liner.
The homeowner had been smelling the result of all this for months without knowing the cause. That musty odor when the AC kicks on is mold spores getting pushed out of the ducts and into the living space. Every cooling cycle was circulating them through the house.
Why This Isn’t Just a Smell Problem
It’s easy to treat a musty smell as a nuisance and nothing more. Light a candle, run an air freshener, move on. But mold in the duct system is a different situation, because the ducts are the one part of your home that distributes air into every room on purpose.
For most healthy adults, low-level exposure might mean nothing worse than a stuffy nose or the occasional headache they never connect to the house. But for kids, older adults, and anyone with asthma, allergies, or a weakened immune system, circulating mold spores can be a real trigger. Coughing that won’t quit. Itchy eyes indoors that clear up when they leave the house. Allergy symptoms that seem worse at home than anywhere else. When those patterns show up and the duct system has visible mold in it, the two are usually connected.
The honest part: we’re an air duct cleaning company, not a mold testing lab, and we won’t tell you every health complaint traces back to your vents. But when a family is smelling must and we pull the registers to find what these photos show, the path forward is clear enough.
How We Cleaned the System
A real duct cleaning isn’t running a shop vac over the vent cover. For a job like this one, the process goes end to end.
We start with a full walkthrough and a vent count so nothing gets skipped. Then we use brush agitation to break the growth and debris loose from the interior surfaces, paired with negative-air extraction that pulls everything out of the system rather than just stirring it around inside. The registers come off and get cleaned separately so the vanes are clear, not just rinsed. We treat the surfaces to address what’s left, and where the duct board is too damaged to recover, we talk with the homeowner about replacing those sections instead of pretending a cleaning will fix board that’s already breaking down.
By the end, the air moving through the system isn’t passing over a bed of mold on its way into the bedrooms anymore. That’s the whole point.
Signs Your Ducts Might Look Like This
You don’t need to pull your registers off the wall to get a sense of whether you’ve got a problem building. A few things are worth paying attention to:
A musty or stale smell when the AC or heat first turns on, especially one that fades after the system has run a while. Visible dust or dark speckling on the vent covers themselves. Allergy or respiratory symptoms that are consistently worse indoors than out. More dust settling on your furniture than seems normal. And the simplest one of all, not knowing the last time the ducts were ever cleaned, which for a lot of homes means never.
Any one of those on its own might be nothing. Several of them together, especially in a home more than a few years old, is worth an inspection.
Close-up of the growth packed into the vent louvers.
Air Duct Cleaning in Richmond and the Surrounding Area
This job was in Richmond, 77407, but we cover the wider Houston and Katy region, including Cinco Ranch, Cross Creek Ranch, Aliana, Grand Mission, and the surrounding communities. Homes out here deal with the same humidity and the same long cooling seasons, and the ductwork pays for it the same way.
If your house has that musty smell when the AC runs, or your vents are showing spots like the ones in these photos, don’t wait for it to get worse. We’ll come out, pull a register, and show you what’s actually in your system before we quote a thing. No scare tactics, no pressure, just a straight look at what’s there and what it takes to fix it.
Call United Air Duct Cleaning at (281) 318-5155, or visit our air duct cleaning page to request a free quote.