Yall ever seen condensation inside a range exhaust vent?

Did a warranty inspection for a client about a month ago. Two days ago he sent photos of condensation collecting inside his range exhaust vent. Says he hasn’t used his range in six weeks or so, nor has he turned on the fan. He just happened to take a peek under the filter and notice a significant amount of moisture on the inside and called me asking how it might have gotten there.

This is a roof-vented unit.

Logic dictates that 1. the air inside the unit would have to be humid, and 2. The unit would have to be at or colder than the dewpoint for condensation to form. It has been humid outside lately down here in central TX but the AC has been blowing inside pretty regularly, thus indoor humidity should be lower than outside. We have had a few showers come and go these last few weeks, but nothing that could have blown moisture inside the vent of the unit.

Any of yall ever seen this before?

Thanks everybody!

I would look at the damper door on the exterior of the home to see if it’s sealing properly. It looks like warm moist air is moving through the duct into the cooler home.


The metal hood is below the dew point, figure out why. If you cannot, get someone who can.

I would follow the vent and check all dampers

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He said it was roof exhaust. But I agree with you, warm air coming in, likely open in the attic (not connected)