Dealing with Moisture Around A/C Vents

Dealing with Moisture Around A/C Vents

Aug 30, 2018
vent moisture

Dealing with Moisture Around A/C VentsThe appearance of vent moisture around the HVAC system supply vents in one or more rooms may be unexplained but it is not uncommon. The vents may simply feel damp to the touch or they may actually be dripping water. In certain cases, dark stains may appear on the wall around the vent due to continuous wetness.

Two factors that are part of life here in our central Florida climate often work together to make wet vents a recurrent phenomenon: high humidity and heavy air conditioner use. Here are some of the ways that combo results in excessive vent moisture.


In summer, the typical Orlando attic accumulates heat and high humidity. Air conditioning ductwork routed through the attic, conversely, is cold. Where hot, moist attic air contacts cool metal duct surfaces, condensation naturally occurs with resultant moisture often saturating attic insulation. As the path of ductwork reaches the supply vent opening, condensation originating on external duct surface saturates the vent box.

Air Leaks

Air leaks that often develop in residential ductwork after 10 years or so are another link in the chain of events that results in vent moisture. When the A/C is running, leaks in supply ducts can suck hot, humid attic air into the cold airflow inside the duct, triggering internal condensation. This liquid trickles down the inside of the duct and emerges into rooms through the supply vent opening.


Evaporator coil shortfalls such as insufficient airflow or low refrigerant charge can result in excessively humid A/C output. As this air enters rooms at the supply vent, condensation forms on the vent surfaces.

Problems of excessive vent moisture may be resolved by installing duct insulation on attic ductwork to eliminate contact with attic air and prevent condensation on external surfaces. Pinpointing and sealing duct leaks also stops infiltration of hot, humid air that triggers internal condensation. Professional service to check the evaporator coil and refrigerant charge, then corrective measures to restore it to specs can remove excess humidity from the system airflow and dry up the vents.

For more about solving vent moisture issues, contact Rinaldi’s Energy Solutions.

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