What size for Vent PVC through roof for Washing Machine?

[Dmcramerica]

I am replacing the DWV in PVC for a washing machine. (Everything was done incorrectly in 1.5” and I am changing it all to 2”.) That said, the current vent up through the roof and boot on the roof is for 1.5”. Can I reduce my new 2” PVC vent to 1.5” PVC at the roof or do I need to maintain 2” through the roof? (Meaning I need to change the roof boot.) Thanks in advance!

 

[Master Plumber Mark]

it wont really matter... leave it alone..... the 1 1/2 vent pipe is big enough

In our area you can have just one 1 1/2 vent for everything--literally for the whole house
sticking out the roof ..... seen this many times.....

so your vent will suffice for the laundry

 

[Sponsor]

 

[wwhitney]

I am replacing the DWV in PVC for a washing machine. (Everything was done incorrectly in 1.5” and I am changing it all to 2”.) That said, the current vent up through the roof and boot on the roof is for 1.5”. Can I reduce my new 2” PVC vent to 1.5” PVC at the roof or do I need to maintain 2” through the roof? (Meaning I need to change the roof boot.) Thanks in advance!

You only need a 1.5" vent starting at the standpipe trap arm san-tee. So you could use a 2x1.5x2 san-tee there. I think that would be better than starting the vent in 2" and reducing at the roof.

If it gets cold enough where you are, there's a concern that a small roof vent can frost over. So a common (required?) practice is to increase any roof vent to 3" just before the vent leaves the thermal envelope.

Cheers, Wayne