Mold In HVAC System-Checking For Mold In Your Home

Mold can be found pretty much everywhere…….

Mold spores can be present in both indoor and outdoor areas of a home and also found in the HVAC System of a home or commercial building. Some types mold spores can be present floating through the air and found on settled dust, but in order for Mold to grow moisture must be present.

Mold only becomes a problem when the spores land on a wet or damp surface. If mold is present and not taken care of it can cause quite a bit of structural damage to the building and its furnishings. We should also recognize that mold can cause health issues so it is improtant to try and prevent mold growth before it gets out of hand.

In this article we are going to focus our attention on the mold problems associated with the HVAC System.

HVAC Ducts and Condensation:

If there is an increase of ninty percent (90%) relative humidity in the air heading downstream of the cooling coils this is considered a normal outcome of the transfered energy betweenthe air and the coils. Moisture can build up and cause condensation on any cold surfaces it comes in contact with by the dampness of the air or the moisture wicking off cooling coils. Particles which are not removed by the filtering system can buildup within the HVAC System. Soil, organic matter, and micro-organisms are a support mechanism to microbial growth if they become damp or wet. If enough moisture is present within the supply ducts of the HVAC system along with dirty ducts can be a place for mold growth to take place

Attempting to look for hidden mold within the duct work can be hard, so it usually will require a Professional with HVAC System Experience if you want to actually locate any water or moisture problems within the system.

Inspecting the HVAC System For Mold: 

To determine if the Air-Handling System is moldy it should be inspected by a Professional HVAC Inspector. Some of the places moisture may collect and become a problem is in the ventilation system. What are some of the root causes of moisture collecting in the ventilation system?

a. poor condensate pan drainage

b. poor roof drainage 

c. high humidity in the ventilation ducts

d. water entering the ventilation ducts from a leaky pipe

e. filters may become damp during the air-conditioning season

f. wet insulation on the inside of the air ducts

A ventilation system that has been contaminated can cause mold spores to spread throughout your home or building and should be mitigated as soon as possible. Consult a professional with HVAC experience and sound judgment to determine the extent of the problem.

Contact A Professional:

You will know if the person you contacted to inspect for mold is a professional because they will look for the following:


a. standing water under the cooling coils of air handlers


b. excessive water in condensate pans


c. drain pans that slope toward the drain (the drain should be flowing freely)


d. ducts are that are properly sealed and insulated 


e. proper installation and maintenance of any in-duct humidification equipment


f. dampness of the filters


g. dirty cooling coils


h. dampness on the acoustical lining


i. humidifier units with stagnant water


j. surface deposits on the air supply registers.

What About The Return-Air Registers:

Just because mold spores are being released in one room of a residential or commercial building does not mean that it is not being circulated to other locations of a building. Mold spores maybe located anywhere in the duct system through which the air is traveling. Spores that become moist by the circulation of air throughout the building through the return-air registers can also be increased by a humidifier utilized in the building. So a HVAC Professional should also inspect the return-air registers for any signs of visible mold growth. Periodic maintenance and cleaning of the ducts can prevent microbial growth inside the ductwork of a building.

Check out the United States Evironmental Protection Agencys (EPA’s) Guide for further information on “Should You Have the Air Ducts in Your Home Cleaned?”   Note: Just because this information has to do with ducts in residential homes it also can be applied to other building types.

Air Sampling The HVAC System:

After a visual examination has been conducted it may be neccessary to take air samples at the HVAC system and from the return-air registers if it is suspected that the ventilation system may be contaminated, and it appears that there is mold growth on the coils, central humidifier, filter or supply registers. Air sampling can assess the extent of the possible
contamination throughout a building.

If you ever have any questions, feel free to leave them below and I will be more than happy to help you out.

All the best,

Troy Halstenson (Founder of Performance Air and Heating)

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