minimum size for washing machine fixture

Hi,

I am in a older house with 2x4 construction. We are relocating our washer. I searched and found that the minimum size for the stand pipe is 1 1/2" for Canada. Can I have a 2" stand pipe going into 1 1/2" p trap? The length of the stand pipe is 29".

Thanks

Mike

What would be the point?

The only thing that will come from downsizing as you go downstream is problems.

No you cannot do that by code.

Jerome2877 said:

No you cannot do that by code.

Click to expand...

Not true at all.

The NPC of Canada doesn't say much about what you can do with a fixture outlet pipe, but only what you can do with a trap and what's downstream of a trap.

Lots of people put 2" stand pipes in when they remodel because it gives you a bit more volume before the washer backs up if you have old, slow draining pipes.

I've seen it plenty of times and it's perfectly acceptable on a retro-fit.

Code issues aside, there are a couple of problems you may encounter. Newer washing machines empty water very rapidly and a 1-1/2" drain is too small to handle it. As noted in a previous answer, the 2" standpipe will give you a small amount of extra space, but may or may not be enough. A pretty basic principle in drain plumbing is that you never reduce the size going away from the fixture. It's rather like a funnel with a large top and small outlet. You can pour a bunch of liquid in the top, but it will empty slowly through the small outlet. Keep pouring water in the top, and it will overflow. If your drain pipes are old galvanized pipes, they also can be half clogged with crud which effectively makes the pipe even smaller.