How to Fix Water Dripping from Ac Vent?

Drip. Drip! DRIP! A steady drip of water from an overhead AC vent is not only extremely annoying, but it could possibly cause a lot of damage. Water and electronics – like computers – don’t mix. Water ruins wood furniture and important papers that might be lying on a desk.

If not corrected, an AC vent or air duct leaking water can even cause structural damage that might cost thousands of dollars to repair. Here are a few reasons why water might be dripping from an AC vent and what you can do to fix it.

How to Fix Water Dripping from AC Vent

Here are the most common reasons and what you can do to solve them. Some are DIY-friendly. Others will require the help of a certified HVAC technician. 

Inadequate Insulation and/or Ventilation in Attic 

When warm, outside air comes into your attic, it is going to raise the temperature of the space around the ductwork. When the humidity and temperature go up, moisture will tend to form more quickly on the cool AC ducts, just as it forms on the outside of a cold beverage glass in summer. 

This moisture can then run down the ducts to the supply boxes where the vent is located. Since the moisture then has a way out, it may start dripping into your room. It might also collect around the vent and begin to soak into the ceiling material, causing additional problems. 

The fix for this problem is two-fold:

(1) Make sure all ductwork in your overhead space is well insulated from the air around it. Make sure that there is a good amount of insulation around the supply boxes all the way down to the top surface of the ceiling material. Don’t assume the attic is well insulated. Sometimes this has been skimped on during construction because it is out of sight. Insulation can also settle over the years and need to have additional insulation installed. 

(2)  Have adequate ventilation in your attic to keep it from getting as hot as an oven. In southern U.S. states the temperature up there can reach 140-150°F without ventilation. There should be a way for fresh air (even if it’s hot) to come into the attic near the eaves, and a way for it to exit at a higher level – either in the roof itself, at the ridge or at gable peaks. 

Pro Tip: Do not vent clothes dryers, bathroom vents or kitchen exhaust into the attic as this will add both heat and moisture to that overhead space, increasing the chance of your air duct leaking water. 

Wrong Size Air Conditioning Unit 

There is nothing you can do about the relative humidity in the air outside your home. But the air conditioner is designed to remove humidity from your inside air as well as cool it. If your AC is sized properly for your home, it should maintain the humidity level at around 30-50%. This is accomplished by the evaporator coil inside the air handler. 

If your air conditioner is too large for your living space however, it will quickly cool the inside air and turn off before it has removed enough moisture from the air. One result of this could be that some of the excess moisture will condense inside the air ducts and find its way to a vent where it will begin to drip. 

The only fix for this problem is to have the correct size air conditioner for your home. You may have to call your local HVAC technician to determine if this is the reason your AC vent is leaking water. 

Very Dirty Air Filter 

Furnace Dirty Air Filter

A very dirty air filter will restrict the flow of air through your air conditioning system. What can sometimes happen is the evaporator coil, which is very cold, will get too cold. When this happens, the water it is removing from the air will begin to freeze on the coil. If this continues, it can become completely covered with frost and cause the system to “freeze up” and shut down. 

Now you have a situation where there is far too much melting water draining into the condensate pan and overwhelming the drain that normally carries the water outdoors. If your AC unit is in the attic, this excess water can find its way to the vents and leak out into your room. 

The fix for this problem is the simplest of all; change the filter in your air handler regularly. Once every 3 months or as instructed in your User’s Manual. If you live in a very dusty area, check it more frequently. Don’t create your own problem by neglecting this simple task. 

Clogged Condensate Drain Line 

Clogged Condensate Drain Line

As just mentioned, there is a way for the moisture that is removed from the air by your AC unit to get outside. It drips off the evaporator coil into a shallow pan, then into a drain line that either goes outdoors or to a floor drain somewhere in the home. If this drain line is clogged, the water will overflow the pan and go wherever it can. With an overhead AC unit, it will almost surely be leaking into attic insulation, through the ceiling or out the ceiling vents. 

To fix this problem, the condensate drain line must be cleaned out. Unless you are prepared to get up into the attic, open the line, clean it out and then reseal it, you should contact a trained HVAC professional to address this problem. 

Roof or Plumbing Leak 

This problem is totally removed from the air conditioning system itself, but may still result in an air duct leaking water. As mentioned above, any water that is on the ductwork can run down the duct until it finds a way out. If this is the ceiling vent, that’s where it will be dripping from. A plumbing leak will most often be constant. A leaking roof might only leak when it’s raining or for a few hours afterward if water has accumulated and is slowly seeping down. 

Sometimes these kinds of problems are difficult to find, but if you or a trained HVAC technician examine the attic space carefully, you can usually find evidence of water leaks. Look for wet insulation, wetness or stains on the underside of the roof, or standing water. 

Don’t Ignore Water Dripping from AC Vents! 

These are some of the most common problems that can cause an AC duct to leak water. There could be others in certain circumstances. If you have the problem of water leaking from an AC vent, don’t ignore it or just place a bucket under it. There could be much more happening that you cannot see that could result in serious and costly repairs later.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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