Duct mold inspection
Visible mold inside ductwork is one of the three conditions the EPA says does warrant cleaning. It is also the most abused claim in this industry, so the order matters: test first.
Be skeptical
Why "we found mold" deserves skepticism
A technician is inside your system with a camera. They show you a dark deposit on a duct wall and tell you it is mold. The remediation quote follows immediately, usually several times the price of the cleaning you booked.
Sometimes it is mold. Often it is dust bonded to the fiberglass lining of flex duct, or discoloration around a leaking joint where humid attic air has been pulled in for years. You cannot reliably tell the difference by looking at a screen, and neither can the person holding the camera.
Testing is not expensive relative to remediation. Asking for it is the single most effective protection against the most common overcharge in this trade.
Where it starts
Where mold actually starts in an Arlington system
Not usually in the middle of a duct run. Mold needs moisture, and duct interiors are mostly dry while air is moving through them.
The wet part of the system is the evaporator coil and the drain pan directly beneath it. That surface is condensing water out of humid air for months at a time, and if the drain line is partially blocked, standing water sits in the pan. Add the organic dust that arrives with the air and the conditions are complete.
Growth then spreads outward from there: the plenum immediately downstream, the first section of the supply trunk, and around any joint where humid attic air is being drawn in. That last one is why sealing is part of a durable fix and cleaning alone often is not.
The inspection
What an inspection should include
- Direct examination of the coil, drain pan and condensate line, the likely source rather than the ducts.
- Camera survey of the plenum and accessible trunk runs.
- A sample taken for laboratory identification where growth is suspected, rather than a visual call.
- Humidity readings in the house and, if accessible, the attic.
- An assessment of whether return-side leakage is pulling attic air into the system.
- A written finding you keep, whether or not it leads to work.
Ideally the testing is not done by the company that would perform the remediation. That is not an accusation, just a structure worth avoiding where you can.
If it is real
If it is mold
Fix the moisture first. Remediation without correcting why the surface was wet produces regrowth, typically within a season here. That usually means clearing the condensate line, correcting drain pan slope, sealing return leaks, and addressing humidity.
On the cleaning itself: hard-surface metal ducts can be cleaned effectively. Fiberglass-lined ducts and flex duct with contaminated lining are a different matter. Porous material with growth in it generally needs replacing rather than cleaning, and replacement is permitted work in Arlington.
Treat chemical treatments with caution. The EPA notes that biocides and sealants applied inside ducts are not well studied for that use, and spraying a coating over growth on a porous surface is not remediation.
Straight answers
Questions about mold in a duct system
Is black dust around my vents mold?
Usually not. Dark streaking at register edges is typically dust deposited by air leaking around the boot, so it marks an air leak rather than growth. Worth investigating, rarely a mold problem.
Should I get an air quality test?
Airborne spore counts are hard to interpret without a baseline, and outdoor levels vary daily. A surface sample from the suspect location answers a more useful question.
Does mold in ducts make you ill?
It can affect people with allergies or asthma. Be aware that the EPA states duct cleaning has never been shown to prevent health problems generally, which is a reason to establish whether there is really mold before treating symptoms as proof.
Can I test it myself?
Home kits exist and mostly demonstrate that mold spores exist everywhere, which is true and unhelpful. If you need an answer worth acting on, use a lab sample from the specific surface.
My house smells musty only when the AC starts.
A useful clue, and it points at the coil rather than the ducts. See coil and blower cleaning. That pattern is one of the more diagnostic things you can notice.
Will my insurance cover remediation?
Usually only where mold results from a covered sudden event, such as a burst pipe. Growth from ongoing humidity or a long-blocked drain line is normally treated as maintenance and excluded.
Start with a survey, not a sales visit
Ask about a mold inspection
Describe what you can see and where, and whether there is a smell when the system starts. Testing comes before treatment here, because "it looks like mold" is not a diagnosis.
Related work we arrange
Related services
Air duct cleaning
Whole-system source removal to the NADCA method: negative pressure on the trunk, agitation in every branch. Not a vacuum poked into a vent.
Dryer vent cleaning
The one job in this trade with a documented fire-safety case behind it. Long duct runs in Arlington two-story homes make it worse.
Coil and blower cleaning
Where the measurable efficiency loss lives. A fouled evaporator coil costs you more each August than dusty duct walls ever will.
Duct sealing and repair
Leaky ducts in a hot Arlington attic dump conditioned air where nobody lives. Usually a bigger saving than cleaning, and rarely offered.