Mold on your Air Conditioner? Causes and Cures.

What causes mold to form on air conditioning systems?  Simple.

Mold is common in environments that have Dirt, Dampness, and Darkness.

Mold spores naturally traveling in the air attach to damp areas then begin to grow.

I often find mold on the exterior of air conditioning systems more often than the interior.  The outside of ducts more often than inside.  Supply air grills (see pictures below) as well on the outside of air distribution plenums and trunk lines than internally.  

When looking for causes and cures for mold growth on air conditioners and heaters you should ask two primary questions:

  1. What is causing water to form?

  2. How do I eliminate the water/moisture?

Mold cannot grown in environments that lack moisture.  Get rid of the moisture and you'll keep the mold from growing. In an air conditioning and heating system moisture occurs due to the mixing of hot and cold temperatures.  Think Condensation.  Same reason cold beverages sweat and create condensation is that same reason hvac systems create mold.  Now we don't find mold growing on our beers or soda cans because we don't give them enough time.

Common causes and cures for mold growth.

  • COMMON PROBLEM AREAS
    • Supply Plenum Mold
    • Supply Air Grills Mold
    • Flex Ducts Mold
    • Trunk Line Mold
  • CURES FOR SUPPLY PLENUM MOLD
    • Remeasure duct sizing to ensure proper airflow through the system (you'll need a professional)
    • replace plenum with higher insulation R value
    • increase distance between ducts
mold buildup on evaporator coil and supply plenum due to improper duct sizing and insulation value.

mold buildup on evaporator coil and supply plenum due to improper duct sizing and insulation value.

mold growing on hvac system

mold growing on hvac system

  • CURES FOR SUPPLY AIR GRILL MOLD
    • Replace grill
    • ensure proper size and fit of grills and ducts
    • ensure that no attic air is penetrating through the supply box 
    • Replace and properly seal supply box keeping attic air from living space.
    • Make sure that home does not have outside air filtration (often caused by construction, negative pressure etc.)
improperly sized supply grill and box

improperly sized supply grill and box

improperly sealed supply box

improperly sealed supply box

mold on supply grill

mold on supply grill

  • CURES FOR MOLD ON FLEX DUCTS
    • Measure ducts to ensure proper airflow through the system (you'll need a professional)
    • Keep flex ducts from touching.  Ducts that touch typically create condensation
    • Install Dehumidifier for attic air (less moisture in the air can reduce opportunity for condensation)
mold on flex ducts that are touching

mold on flex ducts that are touching

moldy flex duct

moldy flex duct

  • CURES FOR MOLD ON DUCT BOARD TRUNK LINES
    • Replace duct board with properly sized ducts.
    • Increase insulation value 
    • eliminate cold air leakage
mold on duct board trunk line

mold on duct board trunk line

flir photo of molding supply trunk line.  Mold especially grows on the cold spots that create condensation.

flir photo of molding supply trunk line.  Mold especially grows on the cold spots that create condensation.

Mold on air conditioning systems can be avoided.  Proper Installation practices and system design will reduce the likelihood of having issues like those shown here.

DO YOU HAVE MOLD ON YOUR AIR CONDITIONING SYSTEM?

If "yes" implore you to have it eliminated immediately.  According to the CDC mold can cause a wide range of effects

David LewisComment