Why is water dripping from my furnace when AC is on?
When the air conditioner runs, water drips directly from the furnace and pools on the ground. This unexpected leaking forces people to constantly mop up standing water and manage basement moisture.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from October 2026.
- This comes up 19.3× 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.
- 1Checking previous posts for similar issuesDid this help you?
- 2Assuming it is normal condensationDid this help you?
- 3Clearing clogged condensate drain linesDid this help you?
- 4running the dehumidifierDid this help you?
- 5mopping up the pooled waterDid this help you?
- 6checking and resetting the condensate pump breakerDid this help you?
- 7replacing or installing a proper P-trapDid this help you?
- 8cleaning clogged vinyl tubingDid this help you?
- 9Placing plastic containers under the leak as a precautionDid this help you?
- 10Having HVAC technicians look at the unit repeatedlyDid this help you?
- 11Considering replacing the entire furnace unit as suggested by contractorsDid 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.
“So this system is causing water to build up in the duct directly under the furnace when the AC is on.”source ↗
“My grandma has had a company come look at it 3 times now over the summer and they can’t seem to figure it out and are trying to just sell her a new furnace because apparently it will always have this problem?”source ↗
“yesterday I noticed a fair amount of water on the ground and I see water dripping from my furnace(see picture) when the AC is on.”source ↗
“We’ve lived in our 1920s Philly row home for just over a year. Our basement definitely has some moisture, but we’ve never had any pooling or leaking water. We went away for a few weeks and came home to this (we had a house sitter staying at the house who had mentioned some water pooling and was running the dehumidifier and mopping it up).”source ↗
“water started coming from the furnace in the last month or so. Do I need to call an HVAC technician or is this something I should be able to fix myself?”source ↗