Water hammer arrestors and code

Hi all,
I'm new to the forum and found it by searching for code information on Water hammer arrestors.
I understand what the arrestors are and how they work but I haven't been able to find if and where code requires them. Some one told me they were required on every fixture but I find that hard to believe. I'm helping a friend remodel her bathroom and I notice the the old plumbing had the old school air chambers (not much good, I understand) and the newer master bath had none installed at all.
Are they required in bathroom fittings or only at quick closing valves?

Thanks,
John

Not sure if they're ever 'required' by code, but functionally, they are useful. Note, often codes state something like "installed per the manufacturer's instructions and local code". Some valves say to install one in their instructions. Now, whether the inspector will ever read them is another thing. They don't cost much, so if you are worried, put them in. Ask the building department what they want (you are getting a permit?).

Well no, she doesn't have a permit, that's why I didn't call the bld dept. I recognize the usefullness of the arrestors but I'm 53 years old and I've never dealt with water hammer problems and her house doesn't seem to have them either. I figure it must be not all that common.

I'll probably put them on the shower valve since it backs up to another tile shower and it would be a BIG problem if it did occur.
I'd put them at the lav and toilet as well if code asks for it but I didnt see a reason to spend the extra $40 otherwise.

Thanks,
John

Water hammer arrestors....

In the UPC (Uniform Plumbing Code) they are required on all automatic valves. In the typical house this usually means water lines supplying dishwashers, clothes washers and ice makers.

That being said, don't bother. They are basically useless. Even the expensive ones don't really work that well. If you have high water pressure, you'd be better off installing a PRV (Pressure Reducing Valve) on the main line and then dial the pressure down to 60psi. Also install a thermal expansion tank if you do this. From there, make sure the piping is secured well. (Note: Water hammer is usually a problem on copper piping only).

I find that the hammer arrestors help.
If you have a pressure reducing valve, then they are required at fast closing fixtures like
Ice Maker
Dishwasher
Clotheswasher

A pressure reducer creates a closed system.


The one on the left is for a washer.
The one in the center can be soldered onto a tee.
The one on the right can be used inline like for a lav supply or an icemaker line.