Yesterday was an extremely hot day here in SoCal with temperatures around 100F. The AC unit had been turned off during the daytime and at nighttime we turned it on to cool down the house.

A few hours later I noticed water dripping down from the soffit right above the upstairs bedroom window on the front side of the house (two story apartment). I don't remember seeing that happen before so I took a closer look and pointed a flashlight at the window where the water was coming from. I noticed a little pvc pipe sticking out of the soffit and that's where the water was dripping out of.

I did some Googling and found some info saying that it could be the secondary or emergency drain of the AC unit, which is where the condensed water goes to when the main drain is clogged. It also said that it's usually in an obvious location so you notice when there's something wrong. I also saw some contrary info saying that it's normal for small amounts of water to come out but that seems to be quite subjective to me.

I turned off the AC after finding out about this, because I don't want any water damage inside of the house. This morning I turned it back on to see if more water will come out, but so far no water.

The actual AC unit is outside on the other side of the house in the back patio.

I've made an appointment with an HVAC company to check this out, but because of the heatwave HVAC companies are completely booked up and I'm going to have to wait for two weeks.

I'm posting here because I would like to find out if anyone can confirm that this is indeed the emergency drain and if it's still safe to use the AC without risking water damage. Could the dripping be caused by the extreme temperatures yesterday while the AC unit had been turned off during the daytime?

Two weeks with no AC is a long time with temperatures like this, so hopefully someone can give me some insight.

This is an image of the pvc pipe: enter image description here

  • Why don't you just go into the attic and trace the pipe? BTW, I'm shocked that your air exchanger doesn't have a float-valve emergency shutdown switch. In MA at least, these are required. If the output drain clogs, the float switch triggers and kills power to the system. Commented Jun 22, 2016 at 15:50
  • 1
    Note that condensation does not occur in the outside compressor unit, but rather inside the ductwork where the cooling coil is.
    – Hot Licks
    Commented Jul 25, 2021 at 1:27

4 Answers 4


I'd suspect it's a secondary drain. It's possible that the main drain was simply overwhelmed, and the condensate level backed up to the point of the secondary drain. If it was really humid, a large volume of water could have been removed from the air. If the main drain is slow, it could have simply not been able to keep up.

Without inspecting the system, it's impossible to say for sure what's going on. If you can follow the pipe back to the air handler, you could confirm that it's the secondary drain. You may also be able to determine if the main line is clogged, and possibly fix it.

If you go poking around, you could post some photos here, and somebody might be able to offer more help.

From the looks of the pipe, it doesn't look like it would cause any water damage. But I can't see if it's dripping on anything important.

  • Thanks for your take on this @Tester101, much appreciated. I do think it may have been that it was overwhelmed, because it's been running since this morning and not a single drip of water has come out so far. To further inspect it I'll have to go up the attic, but I need a bigger ladder to reach that first. Once I get access to the attic I'll check it out where that pipe leads to.
    – Ruben
    Commented Jun 21, 2016 at 20:29

The problem is several things.

Your seeing the secondary drain getting rid of the water because your AC or Heat Pump is outside but you have cooling coils (pretty big) in the attic where the drain tray is. The air cools and condensation forms from water in the air & comes off the line.

Normally you have an HVAC technician service the AC/Heat once or twice a year. (Good idea, your unit runs much more efficient and you can avoid these kinds of issues.)

The pan in the attic is filling. So, you could be giving mice a big drink of water too. (This did happen in a foreclosure I owned leading to the mice making nests out of an 18 vent ducting system on a 70ft trunk run. - cost to replace the whole ducting system)

So what is the issue, mold or spider web inside your primary drain.

In servicing, the tech blows out drain lines, checks coolant (topping off or detecting subtle leaks in the and washes your coils with special cleaner to have the aluminum fins be most efficient. )

The technician also places a disc (chemical) in the pan to retard mold growth.)

Your in the monsoon season and have had rain. Now it is heating up, the water is evaporating and returning to the clouds.

Suggestion: get a service tech out and service your system, they can figure out the real reason. Here the annual service is about $185-200 a year. Cheap preventative maintenance most people don't do but you will pay for it and more in higher energy bills (dirty coils) and problems with drain lines. Out here systems cost 17-22K and more.

Me, business manager for a HVAC company, my husband is the Master HVAC & Master Electrician ...

So, Since I am not there, this is my best guess. Good luck


I have a similar pvc pipe that drains condensation like this too. It scared me at first. But 5 years later and no problems. I thinks its just the backup. Unless you notice some water stains inside the house/wall you probably are ok.

  • Five years later and your pan may be about to rust through, filled with mold, while your main AC drain is clogged up. You still should probably check that out, if it's high up like that it's most likely the secondary, also called emergency (!), drain. Commented Oct 10, 2020 at 23:24

I have seen the same problem every year. The main drain line is clogged and the dripping from the soffit comes from the second line. I used 50-ft auger line bought from amazon and inserted all the way into the main line accessible from the bathroom sink. That solved the problem.

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