buyer home inspector found black mold in ac supply plenum in houston tx - closing delayed, how to clean flex ducts safely?

Question

selling our 2-story home in houston (the woodlands). during the buyer's inspection yesterday, the inspector took a photo inside the attic air handler and found thick black fungal growth coating the fiberglass supply plenum box and spreading into the first 4 feet of flexible ductwork.

buyer's lender won't allow closing until the hvac system is certified clean and tested.

can flexible ductwork with mold inside be cleaned, or does the entire attic duct system need to be replaced? what is the fastest way to get this certified to keep our closing on track?

Antonio · Accepted Answer

Direct Answer:  Porous fiberglass duct board and insulated supply plenum boxes with visible internal fungal colonization are classified as non-salvageable under NADCA Standard ACR 2021 and must be replaced. However, adjacent flexible duct runs and metallic trunk lines can be successfully decontaminated under 5,000 CFM negative pressure vacuuming and botanical antimicrobial fogging within 24 to 36 hours. 
 In Houston's humid climate, air conditioning supply air at 55°F causes chronic condensation when duct insulation is compromised. Fungal colonies (such as  Aspergillus versicolor  and  Cladosporium ) thrive on accumulated dust within duct lining. Spraying liquid biocides into dirty fiberglass is ineffective and prohibited by EPA regulations. 
 The 4-step emergency HVAC closing clearance protocol: 
 
    Plenum Box Replacement:  Cut out and replace contaminated internal fiberglass supply plenum with new insulated metal ductwork. 
    NADCA Negative Air Extraction:  Connect high-volume 5,000 CFM vacuum collection system to supply and return trunk lines. 
    Pneumatic Whip Agitation:  Drive rotary air whips through ductwork to dislodge microbial biofilm. 
    EPA-Registered Botanical Fogging:  Mist all duct branches with hospital-grade thymol biocide. 
    PRV Air Quality Clearance:  Independent consultant collects supply register air cassettes certifying normal fungal ecology. 
 
 Call our Houston emergency HVAC team at  (855) 215-6261  for immediate duct certification.

lisa_m_broker · Answer

In the Greater Houston market, HVAC plenum mold flags on about a third of summer inspection reports. Buyers are terrified of breathing spores through the AC vents. Having the NADCA certificate with passing lab numbers completely puts them at ease.

brian_t_gc · Answer

Don't let a general handyman wipe it with a rag. If spores enter the coil or return plenum, you will cross-contaminate the entire house and fail the buyer's air test.

michael_b_ny · Answer

Update:  Had the air handler inspected this morning. The supply plenum fiberglass lining was completely black. How much does full trunk line fogging and NADCA cleaning usually run in Houston?

Antonio · Answer

Commercial NADCA trunk line cleaning with EPA botanical fogging and plenum replacement runs between $1,800 and $3,500 depending on tonnage and system access. Make sure the contractor provides before/after fiber-optic boroscope photos.

kevin_p_investor · Answer

Agree with Antonio. Had this on a Spring TX flip. Inspector took photos inside the ducts and cleared it next day.

lisa_m_broker · Answer

Michael, make sure your contractor invoices list 'NADCA Standard ACR 2021 compliance' so the buyer's lender doesn't question the receipt.

michael_b_ny · Answer

Final update:  Cleaning completed today, boroscope photos were crystal clear! Underwriter cleared condition in 2 hours. Closing is on for Friday!

buyer home inspector found black mold in ac supply plenum in houston tx - closing delayed, how to clean flex ducts safely?

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