The only thing that is supposed to flow out of your AC vent is cooled air. If instead you notice water dripping from the vent, something somewhere is wrong.
Water leaking from AC vent is usually caused by condensation in the ductwork, frozen AC unit or a clogged condensate drain line. In some instances the problem could be caused by a rusty/cracked drip pan, leaking roof, air leak around the vent, faulty condensate pump or a badly installed AC unit.
To fix a leaking AC vent, start by unclogging the drain line, replace rusty drip pan, seal air leaks around the vent, change air filter, replace faulty condensate pump, fix a frozen evaporator coil, insulate air ducts or reinstall a poorly installed unit. You can also hire an HVAC technician.
If your AC vents leaks water when it rains, you have a leaking roof. The leaking water travels along the ductwork and leaks out into the house through the vent. The leak can happen in both supply and return air vents.
If your AC vents are leaking water during winter, it means that the ductwork is not properly insulated. Condensation therefore happens inside the air ducts (vapor turns to liquid) and water leaks out of the vents.
Condensation can happen during both winter and summer. In summer, condensation happens outside poorly insulated air ducts while during winter condensation happens inside the air ducts and the water drips out through the AC vents.
In summary, the following are the causes of a water leaking out of AC vent:
- Condensation in air ducts
- Air leaks around the vent
- Clogged condensate drain line
- Leaking drip pan
- Faulty condensate pump
- Frozen evaporator coil
- Leaking roof or water pipe
- Improper installation
If your air conditioner is leaking water through the vent, the following are the ways to stop/fix it:
- Have the ductwork properly insulated
- Seal air leaks around the vent
- Unclog the AC drain line
- Replace or fix a leaking/corroded AC drip pan
- Replace faulty condensate pump
- Fix a frozen evaporator coil
- Reinstall poorly installed AC units
- Fix unrelated water leaks
Related: Why your AC is leaking water.
How to Fix Water Leaking from an AC Vent
Let us now look at the causes of water leaking from an air conditioner vent and how to fix them in more details.
Note: The first step in all cases will be to turn off the AC until the problem has been conclusively addressed. You should not continue running an AC that is leaking water.
1. Condensation in Ductwork
A central air conditioner has 2 types of ducts, supply and return air ducts. Return air ducts carry warm and humid air from the house to the AC indoor unit while supply air ducts carry cooled air from the indoor unit back to the house.
As such, there are also supply and return air vents. To prevent heat transfer between the inside and outside of the ductwork, insulation is used.
If the insulation is not done properly or a section of the ductwork is not insulated (especially the supply air ducts), heat transfer between the air inside the vent and the surrounding air will happen.
During the months of summer when cold air is flowing inside the supply ducts, condensation will take place outside the ductwork, the condensate will flow along the ducts and drip out through or around the supply air vent.
During winter, the supply air ducts would be carrying heated air from the furnace or heat pump. If the ductwork isn’t properly insulated, condensation will happen inside the air ducts and hence water will leak out of the AC supply vent.
Note: warm air contains high moisture content than cold air. That is the reason why when the warm air comes into contact with a cold surface the moisture condenses to form water.
Although ductwork installation is something that should be done by an HVAC professional, you can also DIY it. Start by taking off the vent grate and examine if the ductwork is insulated or not.
If it isn’t, try to access your attic and approximate the amount of insulation needed. Purchase the insulation from a home improvement store and wrap it around the ductwork.
2. Air Leaking Around the Supply Vent
After cooling, air is supposed to flow from the evaporator coil through the supply duct and enter the house from the supply vent. That however doesn’t always happen.
If the cooled air manages to leak out from around the vent, condensation can build up and start to drip out through the AC vent. In some instances the ceiling part near the vent will be damp as well after absorbing the water.
This problem is actually quite easy to investigate and fix. Remove the supply air vent grate and with the palm of your hand try to feel if there is air escaping around the vent. If there is indeed cool air flowing from beside the vent, that is the reason water is dripping from the vent.
What you need to do in this case is head over to your nearest home improvement store and buy some caulk (if you don’t have it already). Use the caulk to seal around the vent to make sure that cooled air only flows out through the vent and not beside it.
3. Frozen Evaporator Coil
An air conditioner should not only cool the house but also take care of the humidity. All that happens in the indoor AC unit, also known as an evaporator coil.
When the cold refrigerant/coolant (popularly known as Freon) enters the evaporator coil, the warm and humid air from the house is pulled by the fan and pushed across the coil.
As the refrigerant is cooling the air by absorbing heat from it, the water vapor in the air (humidity) condenses and drips on a tray underneath the evaporator coil known as a condensate drain pan or simply drip pan.
Sometimes this process does not happen as designed. When that happens, instead of the condensate dripping in the drip pan, it ices over the evaporator coil forcing it to freeze.
Although freezing happens in the evaporator coil, it can continue along the path of the supply air duct. After the AC has been turned off, the ice will start to melt and water will leak out of your AC supply vent.
So, why would an evaporator coil freeze? The following are some of the causes:
Dirty Air Filter
Air conditioners are fitted with an air filter to clean the indoor air. Dust, pollen, lint, hair, far, dander and other particles are trapped by the filter (located in the return air duct) to prevent them from being recirculated in the house.
When you fail to change your AC filter, it restricts the flow of warm air to the evaporator coil. When only a small amount of warm air can reach the coil, the refrigerant temperature falls below freezing point causing the coil to freeze.
Replacing the air filter after every 3 months will stop this problem from happening.
Dirty Evaporator Coil
A dirty evaporator coil also has the same effect as a dirty/clogged air filter. Not enough warm air will get to the coil causing it to freeze.
You can clean the evaporator coil yourself or have the HVAC technician do it when they come over for the regular AC maintenance
Blocked or Collapsed Air Ducts
When you have clogged, leaking or even collapsed return air ducts, again warm air will be prevented from getting to the evaporator coil causing it to freeze.
Unfortunately, troubleshooting a clogged, leaking or collapsed air duct is something that should be done by an HVAC professional. It is especially hard for the average homeowner to find leaks or even clean the ductwork.
Low Level of Refrigerant
When the level of refrigerant in the AC system is lower than it should, it means that its pressure is also low. Usually, when the pressure of the refrigerant is reduced, its temperature falls as well.
This means that the refrigerant temperature will drop below 32 degrees (freezing point) and when that happens, ice will start forming on the evaporator coil.
Since the AC system is a closed-looped system, the refrigerant shouldn’t need to be added. As such, it means that the refrigerant is leaking, and you will need to hire a technician to fix the leak and then recharge the AC system.
4. Rusted/Cracked Condensate Drain Pan
As I mentioned earlier, the evaporator coil has a tray underneath it called a drip pan to collect the condensation hence preventing it from causing water damage. From the drip pan, the water is channeled outside the house using a drainpipe.
Some air conditioning units especially those located in the attic have a primary and a secondary drip pan. The secondary drip pan is located underneath the entire unit and is meant as a backup for the primary drip pan.
After many years of usage, the drip pan is likely to corrode and develop a hole or cracks. When that happens, the condensate will leak out as soon as it enters the pan.
Depending on where your indoor unit is located, the condensate can leak out through the air vents and that could be the problem you are experiencing.
Just head over to where your AC indoor unit is located and inspect the drip pan. Is it corroded and leaking? Usually, it will also be leaking from the bottom.
You can seal a small home using a water-resistant sealant but if the entire pan is damaged you will have to replace it. A drip pan is cheap but the replacement cost will be high since it has to be done by a professional.
5. Clogged Condensate Drain Line
The AC condensate drain line as I mentioned removes water from the pan and drains it outside the house. Because of the humid conditions inside the drain line, it is a perfect breeding ground for mold, algae, mildew and other bacteria.
These organisms multiply rapidly inside the drain line and clog it completely. Dust from the indoor air also contributes to the clogging of the drain line especially if you fail to change the air filter.
To check if your AC drain line is clogged, again inspect the drip pan. If it is overflowing with water, it is a sign that the line is clogged. The water from the drip pan overflows and leaks out through the AC vent.
Unclogging an AC drain line is easy. Just locate the drain line outside the house and connect a shop vac hose to it. Use duct tape to create a tight seal
Run the shop vac for about a minute then turn it off. The shop van will suck out the clog and clear the line.
Alternatively, pour a cup of distilled white vinegar down the drain line (from the AC drain line access tee next to the indoor unit) and flush it with water after 30 minutes.
6. Faulty Condensate Pump
Some air conditioners use a centrifugal pump known as condensate drain pump to pump the condensate out of the drip pan. Usually, that happens when the AC unit is farther in the attic or in the basement.
Just like most pumps, your AC condensate pump can malfunction and fail to drain water out of the drip pan. Again, head over to where your indoor unit is located and check if the drip pan is overflowing with water.
That could be the same water leaking out through the AC Vent. Turn off the AC unit immediately until the problem has been fixed.
In this case, you will most likely need to replace the pump, and sadly that is hardly something you can do on your own. You will need to hire a professional to do it for you.
7. Improperly Installed AC Unit
Is the AC leaking from vents newly installed? If it is, chances are high that it was not properly installed.
You see, an AC unit has to be installed on a flat or level surface. If the unit tilts to once side, there is always a chance that it is the side away from the drain opening.
When that is the case, water will pool on that side and overflow even before the drain line has the chance to drain it out. The same water can find a way to leak out through your AC vents.
An improperly installed AC unit will need to be reinstalled. If you installed the unit yourself, I would suggest having a professional HVAC technician come over and do it properly. It will cost you though.
8. Leaking Roof or Plumbing Pipe
Does water leak from your AC vent leak when it rains? It is highly likely that you have a leak somewhere on your roof that lets in water to the attic when it rains.
The leaking water from the roof travels along the AC’s ductwork and leaks out through the vent. This is not an easy problem to fix but nonetheless it needs to be fixed as soon as possible before it results in even more water damage.
If not a leaking roof, you could be having a leaking water pipe. Again, the water from the pipe leak will leak out of your vents whether it is raining or not. It is therefore easy to tell the difference between the 2 types of leaks.
And basically that is why water is leaking out of your AC vents. Although some of the problems here are things that you can easily fix yourself, if you don’t feel comfortable doing it I would suggest that you hire a professional technician to fix that and any other HVAC-related problem.
I hope that this guide was helpful.