Mold Forming in Air Conditioning Vents

Problems with the Air Diffuser Location
Summertime means that the air conditioning is on and cold air is being distributed throughout the home, via air ducts. In many instances these air ducts are located in the ceiling or the floor and are properly placed for maximum air distribution and efficiency. However, there could be a unique situation that occurs if the diffuser is placed in the wrong location on the ceiling or at the floor level.

I just had this situation occur in a home in Florida. The homeowner complained that the air diffuser was always wet and dripping with water. In addition, the area around the diffuser was producing mold growth. These situations concerned the homeowner and she needed some answers.

We noticed that the air diffuser causing the issues, was located approximately three feet from the perimeter of the room. In most instances, an air conditioning diffuser is located immediately along the perimeter of the room with a section of ceiling existing from the edge of the diffuser to the actual wall of less than six inches. This is the common location for both heating and air conditioning vents and diffusers. One of the reasons for this perimeter placement is to ensure that the air conditioning or heating is evenly distributed throughout the room without any unconditioned pockets of air along the perimeter of the room.

However, in some situations there are legitimate reasons for the location of the vent that differs from this common placement. Issues such as physical obstructions causing a shift of the diffuser or in the case in Florida the location of two brick chimneys exposed as architectural features. These brick chimneys caused the placement of the diffuser to project further from the perimeter of the room than normally suggested creating an unconditioned air pocket within the room.

The location of diffusers away from the wall can cause the development of a hot or cold spot in the room. In the case of the Florida situation, the hot spot was an area of space between the two brick flues of approximately three by six feet. To compound the situation, there was a piece of millwork that was placed between the two brick chimney, but only extended to within two feet of the ceiling height causing a perfect space for warm, moist air to accumulate.

The location of the chimney flues in combination with the existence of the piece of millwork had caused a cavity above the millwork of approximately two feet high, three feet deep and six feet long. This thirty six cubic feet of space was not heated nor air conditioned due to the placement of the ceiling diffuser outside this space.

This thirty six cubic feet of space was heating up and absorbing water vapor from the humid bathroom. Warmer air is capable of holding more water moisture than cooler air. This pocket of moist, warm air was sitting above the millwork and between the two chimney flues. When the air conditioning was running, the cold air exiting the ceiling diffuser was causing the warm moist air to condense water vapor on the meta; ceiling vent, as well as the surrounding ceiling. The ceiling was constructed of drywall, therefore the combination of water vapor and organic paper material making up the surface of the drywall was allowing the growth of mold around the diffuser. Mold requires moisture as well as an organic material such as paper or cellulose to grow.

The weather in Florida is extremely hot and humid. This hot and humid environment causes the air conditioning to function the majority of time, and had promoted the development of condensate and mold growth.

It is important to understand that when cold air is introduced into a warm moist environment, the water will condense out of the warmer air as it is cooled. If the entire space is cooled at an even rate and all the air becomes drier and cooler, an equilibrium will be achieved that will stop any additional condensation and water accumulation. However, if there is a pocket of air that is not properly cooled, or there is a continuous inflow of warm moist air into a cool environment, water will be generated and mold will follow.

Solutions to this problem are as unique as the different room layouts and situations that could occur. The primary goal is to prevent any pocket of air to be created that will not be conditioned. If there are pockets of space that are not easily conditioned by the room’s diffusers or ventilation, they should be eliminated by means of blocking them off, redesigning the room layout or placing a specific diffuser in the area to condition that space.

Not only are there reasons of comfort, for equal distribution of conditioned air, there are reasons of practicality. If you are interested in properly air conditioning your home, you must be cognizant of the fact that partial air conditioning will cause issues of water accumulation, excessive condensation and most importantly, mold growth. Partial air conditioning or improper distribution of the cooler air could cause problems.

The cost of properly distributing your air conditioning and heating could be more expensive and involved than partially solving the problem. However, it is important to consider the many different negative results, if the space is not properly conditioned.

Our advice is to hire an expert in HVAC for the best results, and understand that warmer air will hold more moisture than dry cooler air. Any warm pocket of air, if located adjacent to cooler air will cause condensation, water dripping as well as mold growth.