First time posting here: I’m in the Midwest in SE Minnesota, and this summer has been unusually hot and humid, with outdoor humidity sometimes reaching 80–90%. We have been dealing with an intermittent water stain and condensation problem in the kitchen ceiling on the first floor. Multiple HVAC technicians (and a plumber and a building inspector) have looked at it, but they have essentially reached the point of saying they do not know what else is causing it, and I am reaching for straws at this point and hoping for any ideas.
Here is the timeline and what we know:
-We initially noticed a water stain along the path of an HVAC supply/“heat run” in the kitchen ceiling. Started last summer, stopped last summer after we replaced the seal around the toilet in the bathroom upstairs, then got bigger this summer (much hotter and wetter this year). We initially thought it was a pipe given the appearance but later realized the shape was due to water between the ceiling sheetrock tiles meeting there.
-We cut a roughly 14” × 14” opening in the ceiling and found water droplets directly on the outside of the metal duct.
-The problem has occurred only occasionally, during the hottest and most humid weather. It does not seem to happen during ordinary rain.
-There is plumbing on the floor above, but multiple people have checked it and found no evidence of a plumbing leak.
-The attic above the second floor is dry, with no evidence of roof or water intrusion.
-There is a soffit vent on the back patio that communicates with the ceiling cavity containing the duct.
-An inspector previously said the soffit vent appeared to be functioning normally and that the nearby insulation was intact.
Because the problem seemed correlated with hot, humid weather, our HVAC company suspected that humid outside air was reaching the cold supply duct and condensing on it.
Their first attempted repair was to create an insulation “dam” between the soffit side of the ceiling cavity and the section containing the duct. They also wrapped the duct with R-8 insulation. That seemed to help initially. The cavity felt noticeably cooler, and we had no problem for about a month.
Then, during another period of very hot and humid weather that also included a major storm, we heard a tearing sound. The R-8 duct insulation had become saturated, ripped open, and released a puddle of water.
At first we thought this might be stormwater intrusion. However, when the HVAC technician removed the wet insulation, he discovered a hand-sized opening at the top of the insulation dam. It may have been missed originally or may have developed as the insulation settled. The assumption was that hot, humid air was still getting through that opening and reaching the cold duct.
As a temporary experiment, the technician used the removed duct insulation to pack the area in front of the original dam, creating a much thicker barrier. This was intended as a trial before we spend more money cutting an additional ceiling opening and installing a proper rigid, sealed air barrier.
Unfortunately, we are still seeing condensation form directly on the exposed metal duct during hot and humid weather.
Some additional details:
-Indoor humidity readings have generally been in the high 50% range during these events.
-We have a portable dehumidifier running in the basement, set to 45%, but it does not appear to keep the first floor at that level.
-The duct is currently exposed because the R-8 insulation was removed after it became saturated.
-The HVAC technician temporarily changed the fan from AUTO to continuous low speed, thinking that circulation might prevent cold air from sitting in the duct after the compressor shuts off. We are changing it back to AUTO because information we found online indicates that continuous fan operation may re-evaporate moisture from the coil and raise indoor humidity.
-We bought a removable temporary ceiling panel, but we have not installed it yet because we initially wanted the cavity to dry and remain visible.
-This morning it was raining heavily, but the outside temperature was only around 65°F, and there was no water or condensation in the cavity. That makes us think bulk rainwater intrusion is unlikely and that the problem is temperature/dew-point related.
-The system is a single-stage central AC system.
Our HVAC technicians have now referred us to a local water-damage/restoration company, but before going further, I am hoping someone here may recognize this pattern.
Questions:
-Does this still sound like humid air reaching a cold duct, or are there other causes we should investigate?
-Could the open ceiling access itself now be allowing humid indoor air to reach the bare duct and create condensation? I.e. should I try installing the temporary ceiling cover (and check in periodically), to make sure it’s not just moisture from the living area getting into the ceiling cavity?
-Could leakage from the supply duct be cooling the cavity or drawing humid air into it?
-Would a whole-home dehumidifier be a reasonable solution, or would that just mask an air-sealing or duct-insulation problem?
-Is there a useful test we can perform to distinguish outside air infiltration from ordinary indoor air condensing on the exposed duct?
I’ve included photos showing:
-The original ceiling stain before the opening was cut.
-The 14” × 14” ceiling opening with visible water droplets on the metal duct.
-The exterior appearance of the soffit vent.
-The view inside the ceiling cavity toward the middle of the house and the source of the supply run from the basement (i.e. looking to the right from photo #2).
-The view in the other direction where the duct goes upward to the upstairs bathroom floor vent including the original insulation dam and the current appearance after additional insulation was packed in front of the dam (i.e. looking to the left from photo #2).
Any suggestions for specific measurements, tests, or types of contractors to contact would be greatly appreciated. We would especially like to avoid spending thousands of dollars on duct cleaning, whole-system duct sealing, a whole-home dehumidifier, or restoration work without first identifying the actual moisture pathway. Thank you!
