OT:water in flex ductwork

frank

Wherever moisture laden air crosses a temperature differential, the moisture will condense at the dew point. This is not only a temperature point but also a physical location. As an example a warm house in winter weather is full of moisture saturated air which is heated to well above the dew point. The temperature of the air outside the house is below the dew point. This means that the dew point must be located somewhere inside the walls of the house. If the walls are insulated but the vapor barrier is inadequate or missing, condensation will occur within the insulation. This is the situation that is occurring with your ducts.

Flexible ducts are constructed of insulation between an inner and an outer shell of material which is supposed to be waterproof. Although the dew point would necessarily be somewhere within the insulation, no condensation should be able to occur there because the moist air is supposed to be prevented from reaching that point. Since your insulation is being saturated the inner ducting must be compromised. You should be able to correct the situation in either of two ways: additional insulation around the outside of the ducting to move the dew point to a place the moist air cannot reach; or, replacement of the section of ducting with the defective inner section (repair of the inner section itself is pretty much out of the question.) The shortcoming of the second option is that if the temperature outside the ducting gets so cold that the dew point falls inside the inner liner, you will still have condensation in the duct that would have to go somewhere, even if it could not saturate the insulation. In other words, you wouldn't have the problem you have now---but you'd still have a problem.

All the best, Stan