Leaky, Moldy or Wet Air Handlers
Air Conditioning Air Handler Condensate Leaks, Causes of Mold Problems in HVAC Blower Compartments & Ductwork
BLOWER LEAKS, RUST & MOLD - CONTENTS: Mold contaminated air conditioning ducts or air handlers: how to find, cure, and prevent moldy ductwork and HVAC systems. Air Conditioning air handler blower fan unit (AHU) leaks and risk of toxic mold. Air conditioning air handlers - Fan Coil Unit Inspection, Diagnosis, Repair, Replacement
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Air handler blower unit leaks & mold hazards:
This air conditioning repair article discusses the problem of A/C condensate leaks into
air conditioning system air handler units, blower units, or AHU's, (also called fan coil units). Leaks in the air handler can cause rust damage and may invite mold contamination in the AHU or in the HVAC system ductwork. Leaks out of the air handler can also damage surrounding building components such as drywall or insulation.
We include the air conditioner blower fan, air
conditioning system filters in this discussion, and we explain the causes, cures, and prevention of air handler condensate or other moisture leaks that lead to rust, damage, and mold contamination in the
air conditioning system. The evaporator coil and problems of frost build-up in the air handler are also reviewed.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
HVAC Blower Leaks, Rust, Mold
Air Conditioner Air Handler Rust, Condensate Leaks, Wet Insulation, & Mold Hazards
The photograph just above shows quite a bit of rust on components inside this air handler.
More significantly were stains indicating that condensate had blown off of the evaporator coil or otherwise spilled into the air handler cabinet
where it had wet fiberglass insulation there.
[Click to enlarge any image]
Wet fiberglass and other wet insulation material form a potential mold reservoir right in the air path.
If an air conditioning system also lacks a good air filter and thus if it also has become
loaded with organic house dust and debris, combined with water where we don't want it this material also forms a possible growth medium for toxic or allergenic mold inside the air handler or duct work.
The next two photographs (below) show more clearly that condensate has been overflowing the condensate collector inside the air handler.
This air conditioning condensate water has gone where we don't want it: onto the fiberglass insulation and into the duct system. The moldy looking material growing on the
foil face of the insulation was a rather common Cladosporium cladosporoioides mold which we often find inside air handlers and duct systems that have been wet like this.
The right hand photo is a close up showing evidence that the fiberglass insulation has been wet in this area - note the rust stains? We often find
more problematic molds in the Aspergillus sp. genus where fiberglass insulation has been wet, even when no mold was visible to the eye.
Mold on HVAC Air Supply Registers
By simple visual inspection (by the naked eye) it can be difficult to know if the black or gray debris on air supply registers is moldy crud or common house dust (see STAINS at HVAC REGISTERS ). Our photos below show debris deposited on HVAC ceiling air supply registers in a Kentucky building.
In response to a history of a building leak event and odor complaints as well as the appearance of mold on some building walls, we analyzed samples of the dust from the ceiling air supply register shown at left. At right you can see that the dominant particle in the sample was Cladosporium sp. C. sphaerospermum spores were also present in this sample.
While Cladosporium sp. is the most common mold found on earth and while it's just about everywhere, for some people this is an allergenic mold. We don't want it being blown around by our air conditioning system nor its growth improved by mishandling of HVAC condensate.
and/or see MOLD ATLAS & PARTICLES INDEX for a description of the health effects and air quality complaints associated with various kinds of mold.
Don't panic even if you do find small amounts of mold in an air supply register. Even in a healthy building we might expect condensate forming on ceiling air supply registers in some conditions, and thus an accompanying growth of small areas of mold. If that's the extent of mold contamination, ordinary household cleaning procedures are sufficient.
Watch out: if the building leak history or complaint history suggest that a larger mold reservoir could be present, including other genera/species of mold, further investigation is warranted.
More information about the potential of problematic mold growth in fiberglass and more example photographs of this event can be read at FIBERGLASS INSULATION MOLD
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(Sept 17, 2014) Digger said:
New heat pump installed May 30, 2014, both inside and outside units were replaced with the newer technology. Just recently noticed white / gray mold around most of the vents throughout the house. The installers came back and did about five things to "take care of the problem", e.g., retaped all connections, reduced amount of coolant, reduced fan speed, did something with "superheater(??") unit or similar, and suggested I also place a dehumidifier in the crawl space under the house (it is closed in but vented). Did not see any mold in ducts, just around vents and clothing and stuff near them. How do you recommend cleaning the vents, shoes, etc. that are affected?? Would appreciate any help as we will start the cleanup soon. Thank you. Digger Q
mechanical cleaning and sanitizing of ductworks and air handlers may be possible for hard-surfaces (such as sheet metal) but soft surfaces such as fiberglass ducts may be actually damaged by that approach. So the options are to replace the ducts (most reliable) or to seal their interior (can work but has risks). I'd not do any such expensive heroic improvements before a visual inspection and possibly supporting surface testing showed that such work was actually necessary.
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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: firstname.lastname@example.org
Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
Wikipedia provided background information about the definition of HEPA and airborne particle interception
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
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