I have a noise issue that I believe is related to air pressure in my HVAC system. (I have already called my HVAC guy, but he is busy and won’t get here for a week or so and this isn’t an emergency.)
I have a two-story house, with an attic above the second story where the furnace is located. On the ground floor is a laundry room, and in the same access port where the water hookups for the washing machine are, is a PVC pipe that runs down from the attic. That pipe is where I hear an almost constant “bubbling/gurgling” sound.
This has been happening for a few weeks, since I had some HVAC work done. Specifically, I had found out that I had an entire duct line that did not have a damper on it. There are three duct lines is total, one going to the upstairs and two going downstairs. I was noticing some thermostat/AC oddness so I had the HVAC guy come and he saw that this third duct line was constantly in an open state. He fixed it and now my thermostat/AC works properly. However, since that was done I have this noise.
My question is, is there something I need to do to clear the line, or equalize the pressure? Maybe run both thermostats on heat or something? The HVAC guy said something on the phone about possibly needing to add a vent, but I feel like if the ducts are now working as originally intended the venting “should” be adequate. The house is 11 years old, btw, and I am the 2nd owner.
Is this just a little 1" or so PVC pipe you’re talking about? It sounds like a condensate drain and you’re hearing water trickle through it.
I’ve never dealt with a attic mounted furnace/AC, but it’s my understanding that they typically have two drains. One runs outside and a secondary drain that leads to a spot where to somewhere that the homeowner will see it (ie laundry or bathroom sink). The idea being that if the main drain gets clogged, it’ll start using the secondary drain which gets your attention.
So, my WAG, is that you’re either seeing/hearing this secondary drain OR that’s the regular drain and it’s just never made the gurgling sound before. It could just have some mildew/mold growth in one spot making it sound different.
If you have access to the attic (and you’re comfortable going up there), I’d suggest you take a quick look and make sure there isn’t some obvious pan of water looking like it’s about to overflow.
Also, if you can verify that this pipe and the drain pipe in the attic are the someone, you might be able to clean it out.
Thank you. Yes, it’s about a 1" PVC pipe. I know there is an “overflow” pipe that goes directly out the side of the house at the attic level. I’m not sure if the one in the laundry room is the main drain or not. It could be water, but I still hear it if the system is off. I will get up there today and check again, but I checked the pan when I first heard the noise and it was bone dry.
Does it stop eventually? After a few minutes? Hours?
I mean, if it literally never stops, you have something else going on. Even if the coils are totally frozen over with huge chunks of ice, all that ice will eventually melt (but it’ll take a few hours or day and you’d notice the AC not working well).
If really never stops, I’d maybe shut off the main water valve to the house and see if that changes anything, just make sure there’s not something constantly running (and draining) that you don’t know about. Does your system have a whole house humidifier (aka AprilAire) that’s not shutting off?
Also, just to be clear, you mentioned the AC in the OP, but since your username says “southern” and where I am it’s about 35 degrees out…are you heating or cooling right now? Even when things are working normally, heating and cooling create condensate from different places and for different reasons (kinda). Also, is your furnace mounted standing up or laying down?
I am in North Carolina, and other than a brief cold spell last week it’s still warm here. Hit 80 yesterday so we are still in the cooling time of year. I haven’t been really watching it constantly, but I feel like it continues for a long time after I shut both thermostats off. I can easily test that today. I do not have a humidifier.
My WAG, is that it’s just condensate water from the AC. If it’s more humid than normal right now, it could very well just be more condensate (or even some frost/ice buildup) than usual. The drain line could also have a small clog causing the water to drain slower than usual. It could even be that the last guy that worked up there moved something and now the water just sounds different than you’re used to.
The real way to check this would be to let the system run for a while, shut it off than pop off the access panel on the plenum and see what’s going on with the evap coil. Is it iced over, is the drain clogged etc. But you might be able to figure out a lot of these questions simply by listening. Also, the AC coil probably has 2 or 4 drains with the PVC pipe connected to one of them. If you’re feeling brave, you could wait until you feel like the water should have drained (few minutes or so) and back off one of the other drain plugs to see if water dribbles out (suggesting the pan is still full of water).
Go into your attic. You will see a pan under your ac. Add bleach to it, and if you are handy blow the drain line down with air. Bleach will usually fix it.
Thank you. Couple of questions: How much bleach? It’s a pretty big pan. How much force would I need to blow air? Can I use the blower on my wet/dry vac?
No way to say how much bleach. Normally a quart is enough, but you have have extra buildup there. An air compressor is good for blowing the line, but a shop vac may work too. Apply the bleach into the pipe drain (it is connected to the pan) and wait for 30 mins and try blowing into the pipe with your vac.
After you are all done, pour half a gallon of water to see if it is draining well and if you can still hear the noise.
Do you know where the other end of the pipe is? You don’t want to go blowing compressed air through a pipe filled with bleach until you can make sure it’s not going to splash somewhere that could ruin something.
Is there a trap near the end of the condensate drain? If there is a stiff breeze, the pressure differential between attic and drain could be sloshing the water in the trap back and forth. My vent does it to my downstairs toilet when it is windy out.
The condensate pan is inside the AC. The pan underneath is an overflow pan. It should be dry in normal conditions. Don’t put bleach in it unless you want to watch it rust.
The gurgling is coming from the drain pipe that is connected to the condensate pan inside the AC unit. This drain is trapped, like any other drain. Unlike other drain traps, though, is operates at either a slightly higher or lower pressure than atmospheric, that is, it operates at the static pressure at the place where the pan is located in the AC. Which means it is deeper than a standard plumbing trap. When the HVAC technician fixed the damper on your system, the static pressure changed.
The trap that was deep enough before is now not deep enough for this higher static pressure. Air from inside the AC is now pushing past the trap and through the drain pipe, causing the gurgling.
Adding confusion is that the trap can also have a vent, but this is a plumbing vent, and has nothing to do with the air vents on the AC system. A (plumbing) vent on the trap might fix it, but I suspect a deeper trap is the solution.