I'm installing a new central air conditioning unit in my attic. I'd prefer to tie the drain line for the condensation into my existing plumbing system instead of having it drain to outside the house. Is this permissible? I have an 1 1/2" vertical drain line that serves a vanity with the pipe continuing up vertically above the vanity to serve as the vent. I'd like to tie into this line. Should I tie in above or below the T that serves the vanity?

Thanks Kevin

I'm installing a new central air conditioning unit in my attic. I'd prefer to tie the drain line for the condensation into my existing plumbing system instead of having it drain to outside the house. Is this permissible? I have an 1 1/2" vertical drain line that serves a vanity with the pipe continuing up vertically above the vanity to serve as the vent. I'd like to tie into this line. Should I tie in above or below the T that serves the vanity?

Thanks Kevin
Hey Kev,
Code forbids connecting a sump pump discharge, water heater t&P valve and pan drain or a AC condensate line to your drainage. They leave you with a direct opening to the sewer with no seal for sewer gas. However you may "bootleg" a connection into the lav drain providing you tie the AC line in upstream,(above) the lavatory trap. Good luck, Tom

Thanks. That's what I was afraid of. I had thought about the sewer gas, but didn't know if there was a way around it. This definitely has to pass inspection so I'll have to route it directly outside.

Tom, would it be legal if he put in a trap on the condensate drain?

Tom, would it be legal if he put in a trap on the condensate drain?

I thought about that myself but if you connected to the tail piece above the lavatory trap you will have double trapped the condensate drain. ILLEGAL!
Say we tied into the stubout AFTER the lav trap. No double trap here.
However since the AC is off during the winter months, and the air inside a heated house becomes dry, the trap seal in a 3/4" drain could evaporate and let sewer gas escape into the AC condensate pan.
Hey!! The Code Book deals with "possibilities" not "probabilities". Case in point is the dreaded backflow preventer. And now you know the rest of the story. Cheers, Tom