NPSM vs NPT On Freestanding Tub Filler Install

[Odessa Eden]

Hello,
Can someone chime in and tell me if NPT connection to water lines is the universal plumbing code to install a freestanding tub filler? I purchased a tub filler that has NPSM connections and my plumber says it does not meet Code and NPSM straight threads will not seal properly. The manufacturer says "NPSM is a common thread in plumbing applications. Connection to NPT without an adapter is possible with the appropriate amount of sealant and, in their expert opinion, it is sufficient for typical residential applications". Everything I read says you cannot connect the two and that and NPSM to NPT adapter would be needed for proper install in Massachusetts. Can someone provide any insight? thank you!

 

[Jeff H Young]

NPSM is a straight thread like on faucets where a rubber seals it NPT are self sealing but require a dressing of pipe dope and/ or thread tape to insure proper leak free joints so depending on your spout you need a proper mate mixing the threads is not a good idea but its been done leak free but really asking for trouble

 

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[Sylvan]

If you have to second-guess your plumber, it shows little faith in his ability. He is 100% correct

 

[Reach4]

Observation: The nipples for a common water heater can accept either a straight or tapered connection. Some places forbid flex connectors to a WH. Some places require it. I suspect that the flex connectors (which have a gasket) are NPS, but I am not sure.


When using a tapered thread, you use tape or dope. With a gasketed connector, you do not use tape.

I will say that flex lines to WHs seal well.

My point is that if your connection thread is 3/4 or 1 inch, you might be able to use a WH flex connector. You may not find a Falcon stainless steel connector cosmetically acceptable. https://www.plumbingsupply.com/flexes.html It may not be allowed by your codes. I am not a pro.

 

[Reach4]

What are the actual words that the manufacturer uses to describe the connection?
Your statement that

I purchased a tub filler that has NPSM connections

NPSM to NPT adapter would be needed

So which is it? The tub has male, or the adapter needs to be male?
Would your tub be like this one? https://terrylove.com/forums/index.php?threads/freestanding-tub-faucet-connection-advise.42852/
I would presume not, but who knows.

 

[John Gayewski]

The threads are the same tpi count same depth of thread. The difference is one is pitched vs straight (obviously). The straight one will seal on a tapered joint, but it's technically not correct to do so. Produce a signed waiver and sign it for your plumber. He should install it if you say you want him to, but won't hold him liable for any repairs.

He is right is technically not made to fit and therefore against code.

 

[Odessa Eden]

I was able to get the information. Thank you to everyone. This community is amazing

 

[Reach4]

You might post the information that you learned, so the next person can benefit.