Window AC Unit Leaking Water Inside? 6 Causes (+DIY fixes)

“My 8,000 BTU GE window air conditioner is leaking inside the house. Water comes from the bottom of the unit, flows inside on the walls, and the carpet beneath is drenched. Please tell me this is not normal and how to fix it.”

The sudden realization when you see water leaking inside the house from your window air conditioner can be mind-boggling. Do you call the HVAC guy right away? It will cost you at least $200 to fix a window air conditioner leaking water inside the house. Can you fix the window AC unit leakage yourself?

The window air conditioner leaking water inside seems to be one of the worst window AC problems. While you’re thinking about where the water is coming from and how to stop the leakage, the water is dripping and destroying your inside wall, carpet, and furniture.

First thing first:

Don’t panic. Follow these two steps immediately:

  1. Turn off the window unit. This has to be said because a lot of people ask ‘Can we use AC when water is leaking?’. In short, no, you should not use your air conditioner when water is leaking.
  2. Soak up the water leakage inside the house with a towel.

You have probably done that by now. The key thing you want to know is ‘How do I fix my window AC leaking water?’. Right?

Luckily, the window AC unit leakage is the most common and easily fixable problem. Most homeowners with older AC units had to deal with window air conditioners leaking inside the house (usually frozen refrigerant coil, located near the indoor side) or leaking on the outside wall.

why is my window air conditioner leaking water inside and outside
Most common causes of window air conditioner leakage. We will use this photo to explain how you can DIY fixing a leaking window AC unit.

And, despite what your father may have told you, you don’t need to drill a hole into the condensate pan (you might hit a refrigerant line or a wire).

First, you need to check where the water is coming from. After that, you fix the leakage whatever it may be – blocked condensate drain, low refrigerant levels, or damaged condensate pan.

There are 6 causes why a window air conditioner might be leaking. We will go through all of them; one of them is bound to be troubling your unit.

Note: These are the same 6 potential window AC unit causes that every HVAC technician you might call will go through. It’s like a checklist; if it’s not blocked condensation drain, check for refrigerant levels, and so on through all 6 steps. You can check a similar air handler leaking water inside articles for mini split ACs here and an article about air conditioner spitting water indoors here (leaking is one thing, spitting water is another).

You still might call an HVAC guy, of course. But window air conditioner dripping water is usually an easy fix, and if you can probably do it yourself, why spend $200+ for an HVAC guy to do it for you, right?

Let’s start with the most common reason why a window air conditioner might be leaking water inside the house:

1. Window AC Unit Is Leaking Water Inside Due To Condensation Drain Blockage (Most Common Cause)

In 1 out of every 3 or even 2 cases, the water is leaking from the front of the window AC unit due to blocked condensation drain. Luckily, this is the easiest leakage cause to solve.

Function of condensation drain: Every window air conditioner removes moisture from indoor air (works like a dehumidifier). Removed moisture is collected in the condensation pan, located at the bottom of the window AC unit. The condensation drain connects the overflow pan to the drainpipe and allows for normal functioning.

window ac unit dripping water due to condensation drain obstruction
Condensation drain obstruction is the most common cause of window air conditioner leaking outside the house.

Cause of window AC leakage: Condensation drain is partially or permanently blocked. Everything from dirt, mold, leaves, or even dead animals like bees can clog the condensation drain. The result is water being unable to escape from the condensate pan which, in turn, creates a spillover. You will notice that spillage as water dripping (partially blocked drain) or leaking (permanent blockage) from your window unit on the inside or outside; depending on where the window AC is leaning.

How to fix condensation drain blockage: Simple. You have to remove the blockage. Open the backside of the window AC unit and try locating the condensation drain. If you see that it’s blocked, use something thin – a needle, toothpick, thin screwdriver – and release the blockage by basically inserting the thin object into the drain and wiggling it around.

In many cases, this is the only thing you have to do. Turn on the window air conditioner and check if the leakage is fixed. Even if the outdoor temperatures are very high and you have +60% relative humidity, the window AC unit at 100% capacity should drain the excess water without any problems.

2. Water Is Leaking Through A Hole In The Condensate Pan (Older Units)

If your window AC unit has been working without problems for 10+ years, and it only now starting to leak all over the place, you might have a problem with a damaged condensate pan. Older units are especially prone to this cause of water leakage.

Function of condensate pan: Condensate pan collects the water window AC unit removes from the indoor air. This pan is located at the bottom of window AC units and has a less than 2-pint capacity. Moisture gathered there is transferred to the drainpipe via the condensation drain in a normally functioning unit.

window air conditioner condensate pan leaking
Puncture in the condensate pan can cause window AC unit to spill water inside or outside the house.

Cause of window air conditioner leakage: Condensate pan has to be intact. If you have a hole in it or any small dent, the water will start leaking from that hole. Causes of pan damage include an unfortunate puncture being created during installation for newer units, and rusting and corrosion with older 10+ old units that have been working just fine before.

How to fix damaged condensate pan: There is no way around this; the hole or dent in the pan has to be eliminated. If can buy a new condensate pan; in all fairness, they are rather cheap (below $30). But if you want to stop the window air conditioner leakage yourself, you can use water-resistant glue or resin to close that gap in the bottom of the window AC unit.

If you have an older unit and the cause of the condensate pan is due to corrosion, you might have to close more than one gas in the pan. Chances are that new holes will form (progressive corrosion) and you will have to fix this leaking window AC problem several times.

In such cases, buying a new pan or even a new unit might be a better option. As always, make sure you buy a window AC with a high EER rating; you will find the most energy-efficient window AC unit options here.

3. Frozen Evaporator Coil Causes The Window AC Unit To Leak (Due To Dirty Air Filters)

There is a good reason why you should clean the air filters at least twice a year. Before you know it, dirty air filters can cause a frozen evaporator coil. In turn, this will cause the window air conditioner to leak, and even blow hot air (instead of cold air).

Function of air filters: As all filters, filters in the window AC are there to remove larger particles like hair, dust, bugs, and so on. As we’ve learned before, all these impurities can cause condensation drain leakage. If air filters are properly and regularly cleaned or changed, the window AC unit will receive unrestricted airflow and function normally.

frozen cold coils causing window air conditioner to leak water
Dirty air filters will restrict airflow. This will freeze up to refrigerant lines, and that ice melting will cause the window air conditioner to leak inside the house.

How dirty air filters can lead to leakage: If air filters are not cleaned, the airflow over the refrigerant coil will be restricted (even up to 10% lower CFM might be problematic). The refrigerant coil is cold; its function is to decrease the temperature of incoming hot air. If it received less hot air than expected (due to the air filter’s restricting airflow), it will get increasingly colder, and can eventually freeze over. When that ice is melting, it can release up to 1 pint of water, and you will notice your window AC unit leaking.

How to fix dirty air filters (not as easy as it sounds): It should be as simple as ‘change the filters’, right? If you already have leakage, the refrigerant coil is probably still frozen. Changing the air filter will solve the leakage in few running hours, but be prepared with your towel! The remaining ice melting will be leaking through the window air conditioner during that time. To avoid furniture, wall, or carpet damage, make sure to be near the unit until the coil is fully unfrozen and the unit stops leaking.

A frozen evaporator coil might cause serious problems. Leakage is just the start of it; if you have been neglecting the window air conditioner leaking for some time now, other window AC problems might occur in the future. Just be vigilant and keep an eye on the unit even when you solve the leakage problem.

4. Too Low Refrigerant Levels Will Similarly Cause The Coil Freezing-Melting Leakage

Of all the causes of water coming out of the window air conditioner, the low refrigerant levels are the worst. You can fix the small leakage quite easily in a similar way as with air filters. The larger issue you will have to deal with is replenishing the refrigerant levels. You can learn more about how to recharge the freon in the window AC unit here.

Function of refrigerant: Refrigerant is the key to how air conditioners work. Expanding and compressing (that’s why the compressor is for) this fluid generates the necessary heat transfer as per the 2nd Law of Thermodynamics that facilitates the air conditioning system.

low refigerant levels might produce a window air conditioner leakage
Another reason why window AC unit is leaking indoors is frozen-melting refrigerant lines due to low refrigerant levels (hardest to fix).

Water leakage due to low refrigerant levels: With lowering the refrigerant levels, the pressure inside the refrigerant lines will drop. This will reduce the heat transfer the window air conditioner is normally capable of. Through a cascade of reactions, the refrigerant lines will become too cold and will eventually freeze over. When they melt, you will see the window air conditioner leaking water inside the house (refrigerant coil is located near the indoor side of window AC).

How to fix the low refrigerant levels: This may sound a daunting task but with some technical skills you can put the freon in the refrigerant lines yourself. Just follow the article mentioned above, or call an HVAC technician to help you out. Just be mindful that when you refill the freon and the unit is working properly again, the remaining ice around the cold coil might melt, and you want to be ready with a towel when the water starts dripping down the inside wall.

If you need to contact HVAC support, you can use this form here to get 4 free quotes by certified and vetted HVAC technicians.

5. Condensate Pump Is Not Pumping The Water Out Properly (Basement-Level AC Units)

This is only for homeowners with below-ground level window AC units with condensate pumps. It’s one of the rarest causes of indoor window AC unit water leakage; most people can skip it but if you have this exact setup, this information might be invaluable to you.

Function of condensate pump: If you have a below-ground level AC, you will usually get an in-built pump with your AC unit. That pump is used instead of the drainpipe; it actively pumps the gathered water against gravity to the surface for proper drainage.

Water leakage due to condensate pump: Simple enough to understand. If the pump isn’t pumping the excess water to the surface, the condensate pan will quickly be overfilled and you will see a leakage.

How to fix a broken condensate pump: This is probably the one thing you can’t DIY. Built-in pumps should usually be inspected by HVAC specialists. Every unit is different and has a specific built-in pump that, when broken, causes water spillage.

An HVAC specialist will probably tell you that you have to replace the condensate pump to prevent the water from leaking all over your basement. Given these are built-in pumps, that’s not an easy task.

6. Water Leakage After Window AC Unit Installation

If you have just installed a new window air conditioner and it started leaking right away, something is probably wrong with the installation. There are several potential causes for leakage, and the leakage just might be the most apparent sign of improper installation.

Keep in mind that this may also apply if you just relocated an existing air conditioner on another window.

In every case, if you experience a window air conditioner leaking water outside or inside the house, it’s best to redo the whole installation process.

If the leakage keeps repeating after a new installation, the wisest thing is to pick up a phone and call an HVAC installation expert.

Rounding Up Ways How To Fix A Leaking Window Air Conditioner

These 6 causes will solve 90% of leakage problems. Keep in mind that water leaking from within the window air conditioner might be a sign of bigger problems.

If you see that the condensation drain is blocked or that you have a frozen refrigeration coil, you can just fix it and that’s that.

If the water still keeps leaking after the fix, you should check for other causes of leakage.

In the worst-case scenario – if you can’t DIY window air conditioner leaking fix – you can just call an HVAC repair guy and swallow that $200+ bullet.

31 thoughts on “Window AC Unit Leaking Water Inside? 6 Causes (+DIY fixes)”

  1. I bought a Toshiba and it leaks inside i had to drill a hole in back and tilt unit back and f still leaks f water inside f junk

    • New GE unit, same deal, never run across this before in a life of window ACs
      Look at your directions, to see if the unit has a Plug you can remove. Try Tilting it at an angle Towards the ground outside. Thats all I have.

  2. Our 10 year old window AC unit is not leaking…but there appears to be water in the bottom of it because we can hear the fan blades moving thru the water. Should we be concerned or will the excess water evaporate in time?
    It should be said that this unit has worked well with no problems to now. However, we are in the Pacific NW and the heat this year has been unreal…temps 95-105 consistently for the last six weeks. The unit has been running 24/7 for many of those days.

    • Hello Terri, high temperatures and high humidity can cause water access. In time, it should evaporate, that’s right. If the water doesn’t evaporate in a few days, check if the drainage is clogged, that’s the most likely scenario.

      • That’s exactly what I was dealing with and with it 100°f+ for quite a few days, It was on 24/7, without time to shut it off, and let it evaporate!!!..I tilted it back to allow it to drain out the back of the pan, and stop the blades from hitting the water, and found the drain hole and it was just a little restricted, so I almost didn’t notice that to be the problem!!..I cleaned it out and that was all it needed!!, small restriction when running 100% for days needs to be completely clear!!..Do that first and go from there while troubleshooting the problem!!!..Goodluck, stay cool!!

        • Hello Kit, thank you for the input. Yes, when AC starts spitting water, you know the blades must be hitting the water inside the air conditioner. Glad you fixed the spitting unit 🙂

  3. Hi, my AC unit has worked fine for about 5 or 6 years. It just started leaking inside a week ago and drips down the wall onto my carpeting. The bottom of the coil are is very wet but there is no water in the back outside part. When I turn it off it drips very fast. I don’t see a hole or hose where the water is supposed to drain out. Not sure what’s wrong…

    • Hello Daniel, the best thing to do here is to check for condensation drain blockage. You will have to open the unit and find the drain. This seems like a case of a partially blocked drain. That’s the most likely cause.

  4. Our Toshiba AC is leaking at the front bottom in the office we have no idea of why it is doing this. we unscrewed the front and it doesn’t seem to be any wholes. Any suggestions.

    • Hello there, can you see water accumulation inside the AC? You should probably check for the condensation drain blockage (#1 culprit). Checking or changing the filters might work as well. Try going through the article and check if any of the suggestions work.

  5. Thank you so much for this easy to understand article. I believe my problem is #1. My question is, my unit is mounted into my wall instead of sitting in a window…how do I remove the backside of the unit in order to check the drain for blockage?

    • Hello Michelle, in-wall units usually have a sleeve around them. Taking them out might be tricky. In this case, it would make sense to call a HVAC guy to help you out.

  6. Wedge a clean mop string where the condensation drain hole is,rust build’s up there and blocks the drain,the mop string offer’s a way for the condensation to drain past the rust build up.

  7. My father-in-law has had this trouble for quite a few seasons now and we were really stumped why this was happening until he told me that it usually did it when it rained so I decided to check the installation that my brother-in-law did and I discovered that the back side of the air conditioner on the outside was not being sealed around the window so rain was getting in and or anytime anybody watered so this might sound stupid for not recognizing it earlier so I wanted to share this in case somebody else was having the same trouble because when it rained it would go right in and fill the window seal up with nowhere to go but up and out so if you’re having this trouble and everything seems fine seal the outside so rain cannot get in

    • Hello Brian, check if the rain can get into the window AC unit. That’s another option: If the rain gets into to AC, you will likely see leaking indoors as well as outdoor. Hope this helps.

  8. Eight year old unit, only used one month in another house. My first time installing a unit (those fan sides are a pain !!) a month later I see water on the front of the unit. Tilted it just a bit, no more water. Saving this article just in case!! Thanks.

  9. My window air conditioner is spitting out water in the house through the adjustable air vents where the cold air comes in. Why is that?

    • Hello Francine, that’s very unusual behavior. It’s really hard to say why the window AC is spitting out water through the vent. The best thing should be to make sure that all the drainage works fine. If that doesn’t help, calling your HVAC guy is a reasonable move.

  10. My a/c is leaking water which is being kept in the window on the outside of my window is very wet I am afraid it’s going to damage the wood on my window what should I do.

    • Hello Linda, wood on the window usually has a coat that protects it from water. However, you should still take steps to avoid water from accumulating on the wood; that means fixing the leaking AC unit. Go one-by-one over the article, check for drainage problems, and so on. With window AC units, it’s mostly that drain pipe blockage; if you remove that clog, you will probably see the window AC will stop leaking water on the window sill

  11. Hello, had window air conditioner for over 2 years just noticed water coming from front under unit what should I do

    • Hi Sylvia, as specified in the article, just go one-by-one over the main causes for leaking window AC units. Check for condensation drain blockage (in the drain pan), cracked drain pan, and so on. Drain blockage is the most common culprit for window AC leaking water from the front.

  12. I purchased an ac from walmart. They delivered it and I have only had it in my window 9 days and it has water build up. I have had to drain the water out of it. I am not sure why this is happening. When I contacted them they told me if they picked it up I would have to wait 7 days or more for a refund.

    • Hi Kerri, it might be that the drainage is already clogged. These units are waiting in storage for months or even years on end. It is possible that dust accumulated in the drain pipe and clogged it. Anyways, a new window AC unit should be draining without a problem; if not, it’s best to return it.

  13. Thanks for the information here. We just installed a Hisense window AC; turned it on and worked fine. Had it running overnight but even though we had set it at 61, the room never got below 70. In the morning I checked it and there was ICE all over the front. Since it is new, it couldn’t be clog filter, could it? I wonder what is wrong.

    • Hi James, sorry to hear that, icing is uncommon in new window AC units. For a bit of reading, you can check the reasons why window air conditioners freeze up here. From your description, the culprit for the icing can be #2 defective fan motor, #4 refrigerant leak, or #6 wiring problems (from that article).

      Now, the first idea here would be low refrigerant levels. Maybe something pierced the refrigerant lines during storage, transport, and so on. In very limited cases, we see wrong wiring causing the icing. I think here you should use the warranty and get a new unit. Hope this helps.

  14. One additional cause: condensation of in house humidity on a cold bottom of the ac unit. Cold coil condensate water inside the unit. Water drops to the bottom and flows to the back of the unit outside. The water is cold makes bottom to be cold and this is just a thin metal sheet so the air on the other side will condense water above inside window sill. My wife alerted me one day that ac is leaking on the sill. It is a new unit so I did not expect any blockage. I took a flashlight and looked at the bottom. There were hundreds of water droplets on all the bottom surfaces. That day humidity was high. I will try to glue a piece of styrophome on all house side bottom surfaces to create a thermal insulation.


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