revealing duct work

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Sigh… owning a house is great and all, but when there’s a leak in your ceiling? Ugh. Here’s how to prevent and clear a clogged air conditioning drain line.

Going to tell you right now: this story isn’t quite finished yet. I found a temporary solution, but I’m more or less going ahead and posting this so that someone will run up to their attic and immediately take care of this, before you have to deal with a ceiling leak.

Let’s start with what we all know is never a good sign: the dreaded ceiling stain:

stain on living room ceiling

I knew it couldn’t be good. I’ll be partnering with a drywall brand later this fall, and while I was at their headquarters earlier this month (recap coming next week), I heard a quote that proved to be way too ominous:

When it comes to owning a house, it’s not a matter of IF you’ll have a moisture issue. It’s WHEN.

Little did I know how true that was about to be. I’ve always said that my house has a sass all its own, and once again, she interrupted my plans. It was as though my house overheard that quote and manifested an example so I could have a story ready to go. I didn’t want to do a tutorial on ceiling stains, but my house is like, “Drywall? Ok, I got you, boo. Check this out!”

But this, of course, isn’t the project I wanted to do this fall — it’s something else that’s way more exciting and cool.

Frig friggity frig-frig — freaking dammit.

Anyway, I saw the leak and at first thought it might be a sweating/condensation issue. It’s been raining practically EVERY DAY this summer and humid beyond belief. So, I figured that turning the A/C up when we went to visit K’s parents the other weekend might have created a problem, similar to how I learned that leaving the door open might freeze up my A/C (as it turns out, your childhood scolding wasn’t just a “bought air” issue). Working on the deck and shed, I’ve certainly noticed how soggy everything in general has been this summer.

Not to panic, I thought. I‘ll just monitor it and let it dry out. If it did, I could just cover over the stain and be done with it and have learned a lesson. I also had one of K’s brother’s visiting overnight at the time, so I was in a frenzy and really couldn’t spend time thinking on it.

(Which is obviously shortsighted, because ceiling leaks don’t give a damn about your schedule.)

The next day, it started to drip. And I knew immediately it was a bigger problem. So, I grabbed a tarp and a cardboard box and started cutting the ceiling open. I certainly know enough to handle a drywall patch, so it was more of trying to protect ruining the floor more than anything.

cutting hole in ceiling

To humor myself, I put a neglected plant underneath the drip to give the plant a little water. ? Lemons —-> lemonade.

watering plant with ceiling leak

After K and I investigated the drip a little more, we had to keep cutting a hole to find the source. I  suspected that the leak might be further away, since the stain was forming right along a drywall seam (which would make it a path-of-least-resistance type thing, where water would seep through a vulnerable spot, even if the drip behind it originates somewhere else). The leak was coming from inside the house a spot closer to the actual wall/joists, near a duct.

revealing duct work

It occurred to both of us: if you go straight up from this point, it’s between two walls and directly in line with the air conditioner in the attic. DAMMIT. The more I cut, the more it became a steady flow.

filled bucket with water

Tip: If the drip is splashing on your floor, drape a towel over the bucket.

After looking through a number of articles online, YouTube videos, speaking to my dad, and more, it seemed the most likely culprit was a clogged AC condensation line.

How to Prevent a Clog in Your Air Conditioner’s Condensate Drain Line

The purpose of an air conditioner’s condensate drain line is kind of in the name: to drain excess water. As the HVAC system does its thing, water is produced, and it needs a drip line to take that water from the HVAC system in the attic or basement and outside the home (you know, where it won’t leak through your ceiling). You can often locate the end of this drip line outside, near your A/C unit.

There’s also often an overflow line and a drip pan underneath the indoor HVAC system, so that in the case that the line gets clogged, it will fill the pan and reach the overflow line and still run out of the house. So, why did I still have this issue?

attic access

Unfortunately, this whole setup usually doesn’t get much love until there’s damage. Clogs and blockages form from algae and mold buildup. Metal drip pans can rust through. To prevent this buildup, it’s recommended to use distilled vinegar or bleach and pour it into the line at an access point (there’s usually a valve somewhere along the drain line where you can open it and pour it in). Doing so on a regular basis (a good time is every spring just before turning on the A/C for the first time),  you should have no problem. If you ever hear a gurgling, or bubbling sound behind your wall, this would be a good time to check too.

But get this: even if you hire someone to regularly service your HVAC system each year, this is commonly forgotten to be checked on. So first, you have to know about this to even ask the person if they checked it. Anyone see the problem with that???

How to Clear a Clogged Air Conditioning Drain Line

You Might Need


  1. Turn off the A/C power at the thermostat and the breaker.
  2. Locate the drip pan beneath the HVAC system. If it’s got standing water in it, you probably have a clog. Shop vac it out or use a towel to soak up the water. I sincerely doubt you will, but you should also clean the pan with soap while you’re at it.
  3. Go outside and locate the end of the drain opening. Use the shop vac again for a minute or two (put your hand around the valve and end of the shop vac if you want to improve suction, or use some super cheap dollar-store duct tape that never sticks well to anything when you want it to). You might hear debris getting sucked up, but check the shop vac’s contents if you’re not sure. You might also see some really gross sludge fall out of the line.
  4. Locate the access valve (if there is one). It will look like a T-shaped vent with a PVC cover. Using a funnel, small cup with a spout, or similar (I used a watering can with a really narrow mouth), pour a little distilled vinegar or bleach into the line.
  5. Allow it to sit for a little while (go watch an episode on Netflix & come back), then flush with water. Have someone outside on the phone with you when you do this to confirm if the line is now clear.
  6. If the above doesn’t work, you can try snaking the clog, blasting it with a canister of air (my dad does this), or calling a pro (hopefully a guy who will remember to check this for you the next time he services your system).

drain line gun

In my case, not only was my line clogged, but:

hvac condensate drain lines

  • My drip pan was rusted through in one spot. That’s what was causing it to leak in the house, because water wasn’t catching where it should have been.
  • Even if I had known about this prior, my drain line setup had no valve to pour anything into. While this might still work if you can remove the fitting on the edge of the drain pan, mine was stuck on tight and really awkward to move in its current layout. So, we had to cut the line and reroute the water flow temporarily into the overflow drain line.
  • Drain lines are recommended to be slightly titled at a downward angle to better assist with water flow. Guess what — nope.
  • There are a number of turns in mine, so the clog has been building up slowly for years.

What’s next:

As I mentioned, my tale is not quite over yet, but at least we have the A/C running and I’m confident we’ll be able to get this fixed. We’ll need to clear the clog and reroute the drain line back to normal, add an access valve, and replace the drip pan. We’ll probably also look into installing an overflow sensor in the overflow line, so we can be alerted in case it happens again (yay, technology!).

Oh yeah — and patch the hole in the living room ceiling. I’ll have that tutorial for you sometime in the future.

So, now you know! I hope this info someday helps someone prevent a clog and an expensive repair bill. If it does, please come back here and tell me so I know I prevented damage in the process of earning mine. ?

bucket and towels

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  1. So funny you posted this. I got a nearly identical pic texted from a co-worker for the same problem. Except her drywall patch was needed because her husband went into the attic to find the leak and stepped through the ceiling. Oops.

    For all of its issues, I wouldn’t live without AC!

    1. Yikes! Yeah, in an attic you have to be VERY careful to step in the right spots! I added some plywood up in my attic a long time ago that helps me to avoid stepping through (it also makes for useful storage space where none existed before). And yes, despite that it’s causing us some trouble, we went out of our way to keep the A/C working while we make this fix! Can’t bear this summer heat this year.

  2. I almost had something similar. My a/c is in the attic – in the master but it turned out to be a roof leak. I don’t understand putting the a/c in the attic is a thing!

    I do have to repair the ceiling still. I’m not sure I’ve had a strong enough storm to test the repair (it only leaked after many hours of rain). I’ll wait until after hurricane season.

    A/C people in my area are familiar with the need to clean the drain; house inspectors, too. But I guess it’s more of an issue in Florida.

    1. We’ve been getting a LOT of rain this spring and summer, so if it had been a roof leak, it would probably have been a lot worse for us. So, perhaps that’s lucky in that regard. And that’s wonderful that people in your area are aware! I feel very foolish for not knowing — it seems so straightforward now. I’ve had an A/C guy do repairs on my unit a number of times in the last few years that I’ve owned my house, and it’s never come up — a leaking drain pan would have been a noticeable stain to him long before it started dripping through the way it did on the first floor ceiling. I figure that even if I’m educating just one more person about this BEFORE they have a water leak, it’s worth embarrassing myself by admitting I had no idea. A much cheaper preventative cost for sure!

      1. Don’t be embarrassed! I didn’t know about cleaning it until it overflowed (in my previous house) fortunately on tile. But most of my friends knew and when I bought my current house it came up.

        1. Yeah, that seems to be what a lot of the articles said when I researched, too — most people only find out they need to do this once there’s a big leak and they realize there was a way to prevent it!

  3. Our AC is in our utility room (with the washer/dryer, furnace, etc). I noticed water on the floor, which was weird but not terrible because that room has cement floors. The next day I read this post, did some investigating, and lo and behold that’s what it was! So thank you very much for talking about this because I had no idea it was even a thing. (Also, I love your blog! I’ve been reading for years but have never commented until now, so hi!)

    1. YAYAYYAYAYA YESSSS I saved someone from this issue! Woo hoo! That was my WHOLE goal with this post, so I’m so excited that it’s already helped one person fix it before it becomes a bigger problem (or before you spend more money on it!). This just made my day. Thanks for reading along, Natalie!!!

      1. There should be a trap in the line near the unit in the attic. It’s REQUIRED because if it’s not there the condensed water will not be able to drain due to the air being sucked in from the drain pipe and will overflow the internal drain pan and leak out into the outer drain pan, which should normally never have water in it. Most HVAC techs these days hook an overflow switch to the overflow drain outlet (the one with the red cap in your photo.) that is wired to turn the AC off when it senses an overflow. And premium drain pans are made of a special plastic. And they are starting to change Building codes to require the units to be within the conditioned space. They always break in the middle of Summer when it’s 140+° F in the attic. It’s hotter than a sauna. Would you like to work in those conditions?

        1. Not quite sure what you’re getting at here, Henry. You kind of jumped around a bit but I appreciate the info if you could clarify what you think we should check next. I haven’t found a trap and the A/C didn’t shut off at any point either (we turned the A/C off to investigate the leak, but that was us doing it, not any automatic switch or anything). I doubt the drain pan was premium and it’s not made of plastic.

          1. I’m not sure how to help from the one photo you posted. One strong point is that you MUST have a trap in the drain line. Unfortunately it looks like your HVAC was installed poorly in that it does not appear to have enough elevation to allow a trap near the unit. I suppose you could put one outside or in an area near the air handler between a couple of joists. Here is one example of a trap. Some HVAC techs love them some don’t. But it is a good example of a condensate drain trap. They also make the plastic drain pans. Not advertising for them, they are just what I am aware of. Sorry about rambling, I’m doing this on my phone. Good luck!

          2. I really appreciate your insight Henry! We’re definitely looking into all of our options at this point!

  4. How much did it cost to have someone fix this problem? Minus the ceiling? I think I have this problem and just moved in a month ago ?

    1. I didn’t actually have anyone come fix it. We figured out that the main issue was the clog, so we used some of my dad’s tools to try to flush/push the clog loose. In the meantime, we rerouted the condensation to the backup line and ordered a new pan to go under the A/C. I still highly recommend getting the pros involved since this isn’t something most homeowners are confident to tackle on their own, but just so you have the info on what we did!