Do You Have Mold In Your Air Vents?

Waukee Air Duct Cleaning gets many phone calls from potential customers concerned that they might have mold in their HVAC vent lines. They say they have family members who are experiencing illness symptoms and they have no other explanation. Let it be known that every home has mold spores floating around everywhere but these spores are harmless unless they were to colonize. Let’s take a closer look at this issue.

How Does Mold Get In My House?

Mold spores by themselves are microscopic. They enter your home through any available openings like when you open a window or door. If you have fresh air intakes for the furnace or hot water heater, mold spores can enter this way. Bathroom and stove/microwave vents are another entry point. Basically, any possible opening allows mold spores to enter.

Some people might panic and say, “Let’s make sure the house is completely sealed.” That isn’t a good idea as a house needs to “breathe” a little to help prevent indoor air pollution. According to Mike Holmes, Holmes Makes It Right, on HGTV, you must have an HRV if the house is too air tight, it can’t get rid of the stale air that can contain harmful ‘volatile organic compounds’ emitted by plastics, treated woods, carpeting, etc. Sealing the house is not the answer. Again, colonization is the issue. Let’s look at this.

Why the HVAC System is the Ideal Place for Mold Colonization

To understand mold colonization within the HVAC system, all we need to know is that there are three ingredients: (1) dust or debris, (2) air and (3) high humidity. Knowing the ingredients, now we need to look at the HVAC system and see where these ingredients could possibly exist.

The first place to look is at the vent grilles (the vents on the walls, floors or ceilings where the cool air from the air conditioner enters a room). As the cold air enters the room through the vent, it meets up with the warm, humid air inside the room. This can cause condensation (moisture) to form on the vent grille. If there is dust on the grille, we now have all three ingredients (dust, humidity and air). This allows the mold top colonize and grow on the vent grille. Where else can mold colonize?

Mold can also colonize around the A-Coil area of the furnace. The A-Coil sits on top of the furnace heat exchanger and has freon flowing through it when the air conditioner is operating. The furnace blower blows air through the A-Coil and that air captures the cold and then distributes it throughout the house. If the A-Coil components aren’t maintained, this is an ideal place for mold colonization. Here’s why…

As the warm, humid air is blown through the cold A-Coil, condensation forms. We have to have a way to get rid of this condensation. There is a drip pan that sits directly under the A-Coil and it captures the moisture formed on the A-Coil. There is a hose that drains that moisture to a floor drain near the furnace unit. If that hose gets plugged and the water can’t escape, mold will colonize. That’s why you must keep that hose cleared.

How Do You Eliminate Mold When You See it?

When our customers call us and tell us they have mold, we recommend that they use RMB-141 Disinfectant. It is a cleaner and fungicide that cleans as it disinfects. It comes in a spray form. Waukee Air Duct Cleaning carries a bottle in every van to clean up mod around vent covers. It does a nice job of cleaning and disinfecting.

Some people recommend bleach but we don’t go that way as we don’t want any accidents to happen and bleach out somebody’s carpet, etc. The last thing we need is to buy a customer a new carpet!

Make Sure Your HVAC System is the Correct Size

We run into situations where the HVAC system is actually too big and powerful for the house. While some might think it is a good thing since it will run less, saving operational expenses, it is actually a bad thing. For one thing, if the blower is blowing too strong it makes more noise. The second thing is if the air conditioner doesn’t run long enough, it can’t rid the house of humidity. That is the purpose of an air conditioner.

We see many apartments with that issue. Too big of a unit for the square feet of the apartment. A reputable HVAC company will know how to size up a house and install the proper HVAC size.


Mold requires three things in order to colonize: (1) dust, (2) moisture and (3) air. The HVAC system is ideal for providing all three ingredients if not maintained. Keep an eye on the furnace unit itself, especially during the summer months to make sure there is no mold growing near the floor drain where the water from the A-Coil drip pan exits the furnace. If you don’t see any moisture at all, that could be an indicator that the hose is plugged at the drip pan.

Also make sure to leave all vents open so that the HVAC unit can operate for the time necessary to remove the moisture from the house. The HVAC system was sized according to the square feet. Closing off vents makes the unit too big, causing less run time.

If you do see mold, you must identify and eliminate the cause. Once that is done, kill it with a good cleaner and disinfectant.

Waukee Air Duct Cleaning is highly skilled at cleaning the air ducts in residential houses. We can eliminate the dust and debris and we will make the air healthier to breathe. Call us at 515-204-0611 if you have any questions and we will be glad to provide guidance. 

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