Have you noticed an increase in the humidity level of your conditioned air, or foul odors coming from your vents? Have you noticed small stains appearing on your ceilings or walls? The problem could be condensation on your HVAC ductwork.
Condensation on air ducts can be a serious problem. Over time, condensation dripping from your ductwork onto attic insulation can cause it to compress, which lowers its R-value. It can also feed mold growth, and cause ceiling joists to rot and sheetrock to disintegrate, leading to unhealthy air quality in your home, and the need for costly structural repairs.
Condensation on ductwork, also known as “sweating ducts”, can be a problem in all areas of the country, but it’s an especially common problem for homeowners here in the Dallas / Fort Worth area.
Why Does Condensation Form on Ductwork?
Condensation forms when warm, moist air comes into contact with cool surfaces. During periods of high humidity and high temperatures, the conditions are ideal for condensation to form on improperly insulated ductwork in your home’s attic. Here in the DFW area, most HVAC ductwork is run through the attic, and improperly ventilated attic spaces are especially prone to this problem. Fortunately, the solution is fairly easy and inexpensive.
Improperly Insulated or Sealed Ductwork
Insulation keeps the warm, humid air in your attic from coming into direct contact with the cooler surfaces of your ductwork.
Fiberglass duct insulation comes in four basic types: duct liners, duct boards, flexible ducts, and duct wraps. Duct liners are applied to the interior of the sheet metal ducts. Duct wraps are essentially fiberglass blankets. As the name implies, these are wrapped around the exterior of the ducts. Duct boards are used to construct a rigid, angular enclosure around the ducts. Flexible ducts are made up of a reinforced inner core, enclosed in fiberglass insulation and a vapor-retardant plastic or foil film outer layer.
Regardless of the type of insulation used, your ductwork should be completely enclosed and the joints should be properly sealed to prevent heat exchange with the outside air. High-temperature tape or caulk should be used to seal the joints between sections of ductwork. Contrary to what most people understandably think, the so-called “duct tapes” sold at your local hardware store aren’t recommended as they tend to become brittle over time.
Improper Ventilation Around the Ductwork
Once you’ve ensured that your ductwork is properly insulated and sealed, you should check for proper ventilation. Having adequate airflow will help reduce the humidity, and prevent condensation from forming on your ductwork.
Here in the Dallas / Fort Worth area, most homes are equipped with passive attic ventilation which includes ridge vents, soffit vents, gable vents. Most are also equipped with non-motorized roof-mounted turbines.
If these types of vents prove insufficient to prevent condensation from forming on your ductwork, you might want to consider adding a roof- or gable-mounted fan to increase the airflow. These devices are available at most home improvement centers and are available in a variety of configurations. Although more expensive to purchase than conventional electrical fans, solar-powered fans won’t increase your monthly utility bills and are therefore a better bargain over the long run.