Why is my ductwork dripping condensation inside the walls?
Ductwork running from unconditioned spaces into wall cavities collects condensation on its exterior, causing water to drip into walls. This moisture leads to severe fungal growth and structural damage that often requires tearing out the walls.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
- This comes up 21.9× more often in r/hvacadvice than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1ripping out wallsDid this help you?
- 2Insulating the vent line if it passes through the attic to manage temperature differences.Did this help you?
- 3Insulating the sheet metal externally or internallyDid this help you?
- 4Asking online for advice on whether to use a dehumidifier, rewrap ducts, or replace them entirely.Did this help you?
- 5Insulating the ductsDid this help you?
- 6Opening a hole in the ceiling drywall to let cold air flow from the living space into the duct cavity.Did this help you?
- 7Repairing the damaged sheet rock and installing a standard return air grille over the hole.Did this help you?
- 8Insulating the duct using duct wrap with an R-8 ratingDid this help you?
- 9Using foil tape and insulation to seal air gapsDid this help you?
- 10Hiring professional contractors for expensive repairsDid this help you?
- 11Applying duct tape to manage leaksDid this help you?
- 12Searching online tutorials for DIY remediationDid this help you?
- 13Leave the door open after you take a showerDid this help you?
- 14Run a dehumidifier in the bathroomDid this help you?
- 15Lowering indoor humidity levelsDid this help you?
- 16Increasing air movement and flow using whole house or room dehumidifiersDid this help you?
- 17Using central system fans or standalone units to keep air moving near windowsDid this help you?
- 18Insulating around the bootDid this help you?
- 19Setting the thermostat higher (e.g., 72°F) and using floor or table fans for air circulationDid this help you?
- 20Slowing down the blower motor to improve dehumidification across the evaporator coilDid this help you?
- 21Avoiding linear grilles or using single-stage cooling systems to reduce condensation risksDid this help you?
- 22Hanging and adding insulation to uninsulated spots on the ductsDid this help you?
- 23Considering closing off gable vents and opening soffits for better intakeDid this help you?
- 24Slowing down the attic fan to prevent pulling conditioned air into the atticDid this help you?
- 25Sealing air leaks coming from the conditioned living spaceDid this help you?
- 26Placing a bucket underneath the duct to catch the dripsDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“This was the second summer our living room ceiling had condensation seeping through from our ducts.”source ↗
“The 2nd-floor bathroom (interior, now window) keeps getting heavy condensation, and neither I nor the contractor I had out can figure out why.”source ↗
“It's fine day to day, but it seems to occur when it rains. After a heavy storm it looked like someone just took a long shower.”source ↗
“This happens when nobody has just showered.”source ↗
“We have discovered that the ductwork in our walls of the second story have been dripping condensation from the outside into wall cavities.”source ↗
“Needs solution as we are having to rip out walls due to fungal growth.”source ↗
“Noticed water condensing on the closed vent, and saw this. Is it frost? Will I need to replace it?”source ↗
“When I removed a large 4x7 foot patch of drywall due to water damage related to a badly piped condensate line there was a square of plywood sitting between the sheet metal of the plenum and the ceiling drywall downstairs.”source ↗
“I want to replace the drywall I removed but need suggestions on insulating the plenum box.”source ↗
“I noticed while I was down there that ALL of the insulation on her duct work was soaking wet.”source ↗
“It was also steadily dripping off the duct work right off the back of the furnance.”source ↗
“I moved into this house recently and duing the hot days, I noticed that there were some water leak marks on the ceiling of the kitchen and the living room.”source ↗
“turns out that the a/c ducts were right there and were sweating because they are not insulated.”source ↗
“I honestly don't have money right now to rip the entire ceiling of the kitchen and living room. That's why I wanted to ask if this would work.”source ↗
“This part of my ac system has been dripping condensation. What do I need to buy to stop it from dripping on to my things in this closet”source ↗
“Sorry for all the questions but just warp the whole thing? And should I put some around the holes in the walls as well?”source ↗
“The ac cooled air is causing condensation to form and leak onto the dry wall below it, causing damage. What can I do to remediate this before patching the dry wall?”source ↗
“Dude I did call a professional. They cut out the dry wall and showed me the issue and provided a ridiculous estimate. This post was my first attempt to get some DYI info so thanks for your unhelpful advice.”source ↗
“This ceiling vent gets covered in condensation whenever the AC runs, and the ceiling around it gets wet too.”source ↗
“What should I be checking — humidity, insulation around the duct, or an air leak?”source ↗
“In the summer heat, with the A/C running, I have a vertical chase oval duct in the wall that has a crazy amount of sweating/condensation, so much so that I need to have a bucket catch the drips in the semi-finished basement”source ↗
“Our windows get condensation on the inside when the temperature starts to drop. Anything I can do to prevent this? I really don't want the water to accumulate and ruin the wood around the windows.”source ↗
“I am having issues with condensation on my AC ducts and air handler.”source ↗
“I am looking to just get more opinions and collect information before modifying something that is potentially unnecessary and may worsen my humidity and condensation issues.”source ↗
“I have already tried hanging and insulating my ducts in spots where it was uninsulated, but I am still having issues.”source ↗
Where this came up
People with this problem also raised
- 11AC unit leaking water from top rubber seal
- 5Why is there condensation and damp spots on walls only on laundry days?
- 3Does my concentric furnace vent need a cap?
- 2Should I seal or replace leaky return ducts?
- 2How to stop ice dams in tight spaces above second-floor windows
- 2Why does my refrigerator ice maker fill tube keep freezing?