Washing Machine Drain Unvented?

[BrianWithAnI]

I replaced my washing machine and to make more space in the small laundry room did not replace the laundry tub. The original drain configuration had the laundry tub drain straight into the p-trap with a T off the line to a standpipe for the washing machine. The drain runs into the wall behind the laundry room, makes a left turn to the exterior wall, then down to the sewer in the basement floor. This is not the main stack. Where it enters the sewer it connects to a 3" line with a cleanout on top. I discovered today there is no vent on that drain. The house was built in 1994 so I have no idea what the code in Ontario specified for the time, but I'm guessing the plumber used the laundry tub drain as the vent for the washer and the standpipe as the vent for the laundry tub.

I now have just the standpipe going straight into the trap. There is not much horizontal space between the standpipe and the washer but there is room on the opposite side. Do I need to install a T on the standpipe and put in an air admittance valve? Is this acceptable?

 

[Reach4]

Do you have reason to believe there is no vent in the wall?

Regarding where to put an AAV if needed, a sketch or photo would help a lot at understanding your situation.

 

[Sponsor]

 

[BrianWithAnI]

Do you have reason to believe there is no vent in the wall?

Regarding where to put an AAV if needed, a sketch or photo would help a lot at understanding your situation.

Thank you for your reply. Yes, I can trace the the path of the drain line through the wall (thickness of a sheet of drywall) into the sewer.

I took some pics but apparently they are too high resolution. Imagine a p-trap with a 30" pipe rising straight from it. I thought it might be necessary to put in a T and a short horizontal piece, an elbow and a AAV. Imagine an open top number 4.

However, that all said, I have installed the new washer and have the discharge hose in the standpipe. It has run successfully without overflowing. I'm guessing the open end of the standpipe is allowing sufficient air in.

 

[Jeff H Young]

Thank you for your reply. Yes, I can trace the the path of the drain line through the wall (thickness of a sheet of drywall) into the sewer.

I took some pics but apparently they are too high resolution. Imagine a p-trap with a 30" pipe rising straight from it. I thought it might be necessary to put in a T and a short horizontal piece, an elbow and a AAV. Imagine an open top number 4.

However, that all said, I have installed the new washer and have the discharge hose in the standpipe. It has run successfully without overflowing. I'm guessing the open end of the standpipe is allowing sufficient air in.

vents have other reasons for being there example to prevent the p trap from siphoning and having no seal