There are two main ways to solve this problem.
Condensation on ac ducts in attic.
It can also feed mold growth and cause ceiling joists to rot and sheetrock to disintegrate leading to unhealthy air quality in your home and the need for costly structural repairs.
Ductwork located in an attic must be hung properly so that the insulation can do its job.
The condensation forms when air of a different temperature meets the grill box and duct connecting the vent to the air conditioning unit.
Condensation on air ducts can be a serious problem.
When water condenses and drips into your attic or home it can cause a some serious secondary problems.
Persistent ductwork sweating may eventually lead to water damage.
Excessive condensation can also create conditions favorable to mold or mildew forming in areas surrounding the duct itself.
Keeping the temperature of the metal connected to the grill.
What causes condensation on ac vents.
First water dripping off of your ducts and onto your insulation can cause the insulation to compress which decreases it s r value or ability to insulate.
Occasional condensation on a c ducts is not a problem but keeping an eye on the situation is recommended.
When ductwork is touching it forms a very cold spot where they are touching thus condensation begins.
Ducts sweat because the outside surfaces of the ducts are below the dew point of the air in their immediate surroundings.
The simple physics behind sweating is.
You can install insulation on the attic side of the register boot and you can make sure that your duct is adequately insulated.
When the hot humid attic air contacts the cold duct or the cold duct boot the moisture in the air condenses on the cold surface just like the condensation that happens on a cold can of beer.
This type of insulation should be standard but since you have a condensation problem it s obvious that the contractor.
Improper or no insulation of ducts.
The last usual cause for condensation on a duct system is if the ducts are not properly hung or they are touching each other.