How to Deal with Water Around A/C VentsDuring humid Indiana weather, vent moisture may be noticed while the air conditioner is running. Typically, moisture appearing around HVAC supply vents in individual rooms ranges from subtle wetness you can feel on contact, to obvious dripping, to staining of drywall around the vent opening due to chronic moisture.

Factors that combine to cause vent moisture are the environment inside the attic and the metal supply ductwork that conveys cold air from the central A/C.

Where ductwork passes through the attic, hot, humid attic air contacts cold duct surfaces and condensation forms rapidly. Moisture may soak attic insulation around the path of ductwork. As it nears the vent box in the wall of the room, condensation dribbling down the ductwork and enter the room at the supply vent.

When air leaks occur in aging ductwork, warm, humid air may enter the cool A/C airflow and cause condensation inside the duct. If the air leak occurs near the supply vent, condensation may trickle down to the vent opening and into the room.

Other possibilities that may form moisture at the supply vent are insufficient system airflow or a low refrigerant charge. These factors can reduce proper humidity extraction at the evaporator coil, making the duct airflow overly humid and triggering condensation where the air enters the room at the supply duct.


To deal with moisture issues at the HVAC supply vent, try these measures:

Wrap the ductwork with air duct insulation. This not only reduces thermal heat transfer into and out of ducts—which increases efficiency and enhances cooling and heating/performance—it also prevents hot humid attic air from contacting the cold metal duct surface and condensing.

Have your ducts inspected and sealed. If your house is 10 years old, chances are the ductwork is leaking by now. A qualified HVAC service tech can pinpoint leaks and offer sealing solutions. This prevents hot attic air from infiltrating the cold duct airflow and condensing.

Schedule professional service to check airflow at the evaporator coil and measure refrigerant charge.

Ask the experts at Mowery Heating, Cooling and Plumbing about service to eliminate vent moisture issues.

Our goal is to help educate our customers in Brownsburg, Indiana and surrounding areas about energy and home comfort issues (specific to HVAC systems).