Connecting 2 inch shower drain to 1.5 inch pipe

[DIYer442]

I'm replacing a shower that has a 1.5 inch drain with one with a 2 inch drain. PA code still allows using the existing 1.5 inch shower waste pipe. Even though everyone advises replacing all the PVC pipe with 2 inch (which I would like to do), the 3x1.5 Y where the short length (3 ft) of 1.5 inch pipe attaches is essentially inaccessible and so I was going to keep the 1.5 inch line.
For the new drain, can a professional tell me, is it better to reduce from 2 inch PVC to 1.5 inch between the drain and trap or somewhere between the trap and the Y? And why that choice (flow advantages)?

 

[justin_dewan90]

Me personally I would keep it inch and a half if I could. I don't like going from big to smaller pipe. That's just me. But if you are hell bent on it. I would reduce after the trap.

 

[DIYer442]

Me personally I would keep it inch and a half if I could. I don't like going from big to smaller pipe. That's just me. But if you are hell bent on it. I would reduce after the trap.

I couldn't agree more (since the 1.5 inch drain has had no problems for the last 25 years) but the pre-made shower pan I'm using only comes with a 2 inch drain.

 

[justin_dewan90]

Reduce off of the 90 of the trap. Put a 2×1.5 bushing I'm the 90 and go 1.5 the rest of the way.

 

[Matt30]

To keep it to code (mine anyway) you would put a 2x1 1/2” bushing in the shower drain or fixture outlet pipe. You can not reduce the size of drainage after the trap

 

[DIYer442]

To keep it to code (mine anyway) you would put a 2x1 1/2” bushing in the shower drain or fixture outlet pipe. You can not reduce the size of drainage after the trap

Thanks, Matt. I knew I had to reduce somewhere. That sounds like it is the best.

 

[Mikey]

I just had the same problem. We're under UPC 2015 + local mods, 2" required, no reduction allowed without explicit permission from AHJ. Took some cutting & pasting, but we're all 2" now.

 

[TomFOhio]

Jones makes a 1 1/2" brass drain.