water hammer after whole house copper repipe

Question

I recently had licensed contractor came replace the whole house repiped to copper and pass the city inspection. However, this also introduce the water hammer into my house.

Layout

• Wash machine - arrestor installed
• Kitchen faucet - arrestor installed
• backyard faucet
• frontyard faucet
• bathroom 1 faucet
• bathroom 1 toilet
• bathroom 2 faucet
• bathroom 2 toilet

the furthest faucets from main valve are bathroom 1 and 2.

Problem

when kitchen faucet turn off from kitchen, I can heard the hammer sound right underneath the bathroom 1,2. however, I don't heard any hammer sound from kitchen faucet itself.

when bathroom 1,2 faucets hot/cold turned off, I heard the hammer sound.

when bathroom 1,2 toilets filled , I heard the hammer sound.

What I had tried

1. drain the entire house, wait for 5 - 10 mins. turn on the main water valve. The hammer sound goes away for 5 mins, then it comes back in again.
2. I called my licensed plumber and they also couldn't figure out why, and started claim this is normal for a house with crawl space

Havn't tried

I am wondering if adding arrestors at 2 bathroom faucets and toilets would really help or not. Because my plumbing guy told me these will not really solve the issues and will involve additional labor and work to cut the wall to install them.

Its really annoying and would like to have some input from you. Thanks!

Answer 1

If the supply valves for the sink (farthest away) are screwed onto a stub of the copper pipe with a male adapter (they should be), then you can simply put in a tee on that pipe, a close nipple to re-attach your supply valve, and in the top of the tee, facing up, install an arrester or even just a piece of pipe with cap on the end to trap air in it.