09/03/2026
New HVAC (2 months old) — plumber + his HVAC guy say it’s missing a P-trap and causing air in the house, installer says it’s fine. Who’s right?
Installed a new HVAC system in my condo about 2 months ago through Company A. System has been running fine, no issues I’ve noticed day to day.
Unrelated to the HVAC, I had a plumber come check the apartment for a possible moisture issue elsewhere. Very thorough guy — while he was here he looked at the HVAC setup and said it wasn’t installed correctly. He video-called his HVAC contact on the spot, showed him the setup, and that guy agreed.
Here’s what they’re describing:
• There are two vertical pipes near the unit. Pipe A comes down from the furnace/coil and currently just runs open at the top — no trap.
• Pipe B is a second pipe at the bottom open at the top after cutting pipe A and they said that one is fine to leave open.
• Their recommendation: cut pipe A after it goes down, install a P-trap there, tie it into the floor drain via a T-connector along with pipe B, and cap the top of pipe A with a removable cap (not left open).
• Their reasoning: without the trap, air is moving through the line, and it’s causing more condensation/moisture in the house — which ties back to the original moisture issue I was trying to diagnose.
I called Company A (the original installer) to ask about this. They came out, looked at everything, and said it’s installed correctly, working perfectly, no changes needed — and that air coming out of the pipe sometimes is normal for this setup.
So now I’ve got two independent guys (plumber + his HVAC contact) saying it needs a trap, and the original installer saying it’s fine and that’s just how it works.
Photos of the setup are attached. Would appreciate opinions from anyone in HVAC/plumbing — is an untrapped open condensate line actually normal in any configuration, or does this need the fix they’re describing? Trying to figure out who to believe before I pay for work that may not be needed (or skip work that actually is needed).
Thanks in advance.