Serious question, is water hammer still a thing with modern PEX?

Back in 2010 I used to install copper with expansion loops on every riser at the Mercy Hospital annex, and we never had hammer issues. Now on a retrofit at a 6-story office building downtown, I see guys running PEX without any arrestors and it makes me wonder if the pipe material alone solved it. Has anyone actually tested this side by side on a commercial system, or are we just lucky so far?

3 comments

3 Comments

river1901mo ago

You're giving PEX too much credit. Ive seen plenty of hammer issues with it on multi story commercial jobs when theres fast closing valves or washing machine hookups. The pipe might flex a little more than copper but that doesnt mean the shockwave just disappears. Without arrestors at the right spots you still get that bang and it can even work fittings loose over time. Your old expansion loops on copper actually did something, but PEX alone isnt a magic fix.

spencerl321mo ago

Blame the install not the material, PEX with arrestors is fine and copper hammers just as bad without them.

michaela161mo agoTop Commenter

Did you try putting the arrestors right at the washing machine box instead of further down the line? I had a similar issue in my last house and moving them closer to the fixture fixed the bang every time... @spencerl32 is right that PEX itself isn't the problem if you treat it like copper and plan for those fast closing valves.