Thread: gulping noice in bathroom sink when ac is on

Hello,

I have attached pictures of my AC and the p trap under the sink. My house is about 15 years old. I'm trying to solve the gulping issue. I'm wondering if the condensation drain pipes are correctly installed. I know for a fact the p trap is not an issue because I have disassembled/disconnected the pipe from the p trap and still the gulping noise continued. I could feel the air from the ac and see the condensaction water come through the pipe. Is there a way to stop this issue? Thank you for your help!

John

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Hi John,

Assuming the "gulp" is only happening when the AC is on, I'd think at least one culprit may be positive pressure from the condensate drain line (a bit of air might be getting induced into the trap). If you attempt to open the pop-up stopper a bit more, does the gurgle stop?

Notice the small "stack" upstream from trap from the pictured condensate drain, this would allow for a neutral amount of pressure in the condensate drain line.

Just a thought.

Hi Tim,

Thank you for your reply. I was attempted to install a trap like one shown in your picture but don't really know if I have the vertical space to do it.

John

you're welcome...

I noticed (and removed/replaced) the picture I uploaded... it was a defective trap install....I thought I had another picture for reference.. seems most pictures we take of stuff like that is of defective installs.

The open portion adjacent to the trap should have been *after* the trap, if present. Otherwise, conditioned air would simply blow right out of it.

Good luck!

You need to install a trap and riser (vent) in the primary condensate drain pipe adjacent to the evaporator coil of the A/C unit. Additionally, you must insure that the drain piping runs continuously downhill from there to its termination above the bathroom sink trap. Any low spots will form shallow traps.

If the above does not stop the noise, the sink may be improperly trapped.

Originally Posted by Aaron Miller

You need to install a trap and riser (vent) in the primary condensate drain pipe adjacent to the evaporator coil of the A/C unit. Additionally, you must insure that the drain piping runs continuously downhill from there to its termination above the bathroom sink trap. Any low spots will form shallow traps.

If the above does not stop the noise, the sink may be improperly trapped.

Keep in mind that the 2" shown in the trap drawings is the MINIMUM trap required for basically any unit, some require a 3" trap, a 4" trap, and I have seen several which required a 5" trap. The depth of the trap is based on the static pressure in the air handler, the higher the static pressure, the deeper the trap needs to be.

The trap should always be located as close to the air handler unit as possible, some manufacturers even state that the trap must be within 4 feet of the air handler unit - but if you physically cannot put a trap at the air handler unit because you do not have the vertical height (and you do not want to have the air handler raised to get that vertical height), then place the trap between the condensate line and the connection to the sink tailpiece.

As shown, your connection is through an air-break, it would be better through an air-gap, but that can create its own problems when connecting under a sink like that - you would want the air-gap to be above the overflow level of the sink.

Thank you for your replies. If I install the trap and the riser, will the gulp noise stop? Can you please let me know? Thanks!

Originally Posted by John Lee1

Thank you for your replies. If I install the trap and the riser, will the gulp noise stop? Can you please let me know? Thanks!

The gulping noise is caused by the air handler sucking air up through the condensate drain line, a proper trap should stop the air handler from sucking that air up through the condensate drain line, thus the noise should stop.

Originally Posted by Jerry Peck

The gulping noise is caused by the air handler sucking air up through the condensate drain line,.

Maybe I'm wrong, but it seems that on every drain line that I've notice, air was blowing out, not sucking in.

Thank you for the replies. But, my ac is blowing the cold air out and making the gulping noise.

Originally Posted by Rick Cantrell

Maybe I'm wrong, but it seems that on every drain line that I've notice, air was blowing out, not sucking in.

Originally Posted by John Lee1

Thank you for the replies. But, my ac is blowing the cold air out and making the gulping noise.

That means that the blower is before the coil (blowing air through the coil) and is creating a positive pressure at the condensate drain pan and its openings to which the condensate drain lines are connected. Positive pressure means the trap needs to be deeper and area of a slightly different configuration.

Most that I see have the blower after the coil (sucking air through the coil) and is creating a negative pressure at the condensate drain pan and its openings. Typically, these requires traps which are not as deep as the positive pressure units.

Thanks Jerry for your reply. Since I don't have the vertical space to install the trap, do I need to cut the sub floor to make the space or do you have a better idea?

John

Originally Posted by John Lee1

Since I don't have the vertical space to install the trap, do I need to cut the sub floor to make the space or do you have a better idea?

Put it here:

Originally Posted by Jerry Peck

but if you physically cannot put a trap at the air handler unit because you do not have the vertical height (and you do not want to have the air handler raised to get that vertical height), then place the trap between the condensate line and the connection to the sink tailpiece.

Looks like you don't have any real options to that location.

If it is a horizontal unit in an attic perhaps you could raise the entire unit and add the trap.

Originally Posted by Aaron Miller

If it is a horizontal unit in an attic perhaps you could raise the entire unit and add the trap.

Unfortunately, the photo does not show if the unit is confined to where it is by the trusses or not.

That is why I said:

Originally Posted by Jerry Peck

but if you physically cannot put a trap at the air handler unit because you do not have the vertical height (and you do not want to have the air handler raised to get that vertical height)

Great minds think alike ... okay, my mind is not great, so, still I thought like you did.

JP: Sorry, missed that..

I’m just curious, is this plumbing method acceptable in your areas, or what code do you reference? In WI this would be a code violation under DSPS382.33 (8)) the sink trap is not an approved receptor for indirect waste.