3rd drain from HVAC Unit ?

[Joe Reilly]

I found this odd, as most units I have seen have 2 drain lines for a HVAC unit, and I understand that upright systems do not even require a secondary drain to be connect as most of the time they are plugged.

I have not seen 3 drains coming from a unit !, Am I just lucky enough not to have seen this before or is it truly uncommon ?

I am writing it up and I figure anything draining needs to drain some where and not on the platform.

Why 3 ???34645

[Dom D'Agostino]

and I understand that upright systems do not even require a secondary drain to be connect as most of the time they are plugged.

34645

Can't imagine why that would matter. Horizontal and vertical cabinet installations both require the exact same condensation drain systems, including secondary. Which leads to...

Regarding your photo, the coil's drain pan simply has been designed to allow 2 drain ports no matter which orientation is chosen for the install.

[Gunnar Alquist]

Oh, I get it. The topmost plug can be removed for the secondary drain if the coil box is on its side.

Lower/right, primary drain if vertical install
Lower/left secondary drain if vertical install or primary drain if horizontal install.
Top, secondary drain if horizontal install.

Dom, you are smarter than you look (or smarter than me, whichever your prefer).

[Joe Reilly]

That actually makes sense... :)

[Jerry Peck]

But ...

Both condensate drains require traps, and if that shadow below the drain elbow is just a shadow - where does that drain to?

[Joe Reilly]

But ...

Both condensate drains require traps, and if that shadow below the drain elbow is just a shadow - where does that drain to?

It did not drain anywhere, yes.. I wrote it up :)

[Lon Henderson]

But ...

Both condensate drains require traps, and if that shadow below the drain elbow is just a shadow - where does that drain to?
Where is a requirement for both to be trapped? I never see the "back-up" or over-flow drain trapped. Since it does not go directly to and into a DWV, I don't know of any requirement for a trap. For one thing, there would never be water in the trap, since the back-up drain never has condensate coming out, unless the primary is blocked. And the purpose of the back up drain is to make a mess that alerts the homeowner to a problem with the primary drain. What I see in the photo, is a typical installation.

[Jaeyoung Lee]

Where is a requirement for both to be trapped? I never see the "back-up" or over-flow drain trapped. Since it does not go directly to and into a DWV, I don't know of any requirement for a trap. For one thing, there would never be water in the trap, since the back-up drain never has condensate coming out, unless the primary is blocked. And the purpose of the back up drain is to make a mess that alerts the homeowner to a problem with the primary drain. What I see in the photo, is a typical installation.

Without traps the cold air in the unit can escape (since there is a drain pipe size hole on the housing!) which lowers the system's efficiency. To make the traps work, you need to fill the secondary drain pipe trap with water (the main trap will be filled with condensate water anyway). Secondary drain pipe needs an emergency drain pan underneath the unit. And, another emergency drain line should be installed from the drain pan to outside of the building or visible location for notifying/alarm so the owner/tenant can clean the primary drain line. Please see another post in "HVAC condensate drain pipes".

[Lon Henderson]

Without traps the cold air in the unit can escape (since there is a drain pipe size hole on the housing!) which lowers the system's efficiency. To make the traps work, you need to fill the secondary drain pipe trap with water (the main trap will be filled with condensate water anyway). Secondary drain pipe needs an emergency drain pan underneath the unit. And, another emergency drain line should be installed from the drain pan to outside of the building or visible location for notifying/alarm so the owner/tenant can clean the primary drain line. Please see another post in "HVAC condensate drain pipes".
In a nonexistent universe, an OCD homeowner might keep the traps full, but in our universe, that doesn't happen. The amount of air escaping these drains is not significant enough to be a consideration. I've never seen a drain pan under the back-up drain or a water leak alarm underneath one...but cheerfully agree that both ideas are good. The best solution is an inline shutoff like a Safe-T float valve switch on the back-up, but everything in the OP's photo is permitted every working day of the week around these here parts.