Noise from main AC drain below bathroom sink

[Gene South]

In the southern USA, where HVAC units are commonly installed in the attic, the primary condensation drain is often connected to a bathroom sink drain (see diagram). Many times this produces a noisy drain. The noise is often described as "gurgling" or "wind noise". Does anyone have any first-hand experience on how this noisy drain issue can be resolved? I know a lot of people speculate on how to resolve it.... but I am wondering if anyone has first-hand experience at resolving the noise. Reconfiguration of condensation drain lines has been suggested however I don't know if that is the correct solution.
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[Jerry Peck]

Insufficient trap on the air handler condensate drain - see the attached documents.

[Jim Luttrall]

Insufficient trap on the air handler condensate drain - see the attached documents.

Agreed.

95% of units around here have missing or improper condensate traps. Many of the remainder are improperly not deep enough to function without gurgling.
The gurgling comes when air is pushed or pulled through a trap that is too shallow or too high in relation to the pan. A trap without the vent can also gurgle or loose the seal, just like and "s" trap in household plumbing.

If plumbers constructed the traps they would likely work better since they understand the principle behind traps and venting. I can tell you from experience that little training is ever given to this in a/c technician training.

[Mark Reinmiller]

I agree about the trap.

Related to this, a few months ago I was in S.C. In the men's room of a church there were three sinks. The center sink had a pipe connected to the trap assembly. If I recall, it might have tapped right into the side of the trap. The tubing was about 3/8" chrome plated and I believe connected with a compression fitting. Does that match anything you see for condensate drain piping?

[Jerry Peck]

Related to this, a few months ago I was in S.C. In the men's room of a church there were three sinks. The center sink had a pipe connected to the trap assembly. If I recall, it might have tapped right into the side of the trap. The tubing was about 3/8" chrome plated and I believe connected with a compression fitting. Does that match anything you see for condensate drain piping?

The tapped of pipe was tapped off at a downward angle instead of an upward angle - right?

That would be the trap primer for the floor drain.

Water flows down in a spiral, clinging to the inside surface of the drain, when the water reaches that tap, the water flowing past the opening flows into the tapped pipe and down to the floor drain, keeping water in the floor drain trap so the water doesn't evaporate out and leave a dry trap with no water seal.

[Mark Reinmiller]

The tapped of pipe was tapped off at a downward angle instead of an upward angle - right?

That would be the trap primer for the floor drain.

Water flows down in a spiral, clinging to the inside surface of the drain, when the water reaches that tap, the water flowing past the opening flows into the tapped pipe and down to the floor drain, keeping water in the floor drain trap so the water doesn't evaporate out and leave a dry trap with no water seal.

Jerry, Thanks. That is one I have not seen before. The pipe may have been at a slight downward angle, but if I recall is was close to level. I could only see about a foot or so to where it entered a wall, which may have been concrete block. The other side of the wall was a hallway and nothing visible there.