Metric pex tubing with imperial fittings

[Coolwhip]

Hi, sorry not a boat owner but I had a question I figured you guys would have ran into this the most...I have been getting mixed answers from plumbers.

Will metric pex work with imperial fittings? I think I'll be using press fittings, but it'd be nice to know for other fittings as well....same question for both pex-al-pex and oxygen barrier if that makes a difference...I can get metric tubing for really cheap and just want to use it for under floor, then mate it with imperial tubing above floor.

Would some sizes work but not others? It also seems MM pex uses the OD for the nominal size, and imperial uses the ID for nominal size(or close it it), is that correct?

 

[JK_Boston_Catalina310]

Basically there are 3 pex options, marine (15 mm), imperial (1/2-3/4 inch most common) and metric (16 & 20 mm most common). All can come with options to connect to threaded pipe but finding connections to go from metric to imperial threaded pipe can be really difficult.

To me it seems like an unneeded hassle since to plumb a house, or a boat, you will spend more money on the fittings than the hose. The hose is the cheap part of the install. So you would have to be getting it for free for me consider the hassle of metric pex in an imperial country. Unless you just really want to piss off the next owner. Imagine the frustration of going into a home Depot with a metric pex and trying to find a fitting.

Good luck

 

[Coolwhip]

So imperial fittings wouldn't work with metric pex....even in the cases where they are very close to the same size? For example, pex-al-pex DN 16 ID is 0.473 inches....1/2" pex ID is 0.475 inches...which is mostly what I am working with.

Was hoping I could just get imperial 1/2"-to-(whatever size) pex-al-pex and fit it straight to the metric stuff...I can get fittings for either/or so getting DN16 fittings to work within the metric pex is no big deal...but I was hoping I wouldn't have to find special fittings/rig something up to change to imperial pex of a different size.

It's not quite free, but I got about 1000ft of DN16 pex-al-pex for just over $100....if no one can tell me that DN16 pex-al-pex can use imperial fittings, I will just get metric fittings and figure something out for those few places where I need it to change back to imperial(not 1/2").

But if I could use standard imperial fittings to change the DN16mm(1/2") to 1/4" or 3/4" that would be great, or maybe use metric fittings to change back to actual 1/2" pex and THEN change size, if not I will just find a way to change it back to imperial THEN change size.

As far as the next homeowner, probably sounds bad to say not my problem...but really, there should be no reason for him to be touching the metric pex...around every fixture, around every system which involves parts that could break(pumps, boilers, etc.) it will all be imperial.

Maybe I will be guinea pig and then report back...if you could use standard 1/2" fittings on DN16 pex, and then either use imperial fittings to change back to metric pipes OR use metric fittings not to change size but to change back to actual 1/2" pex and then change size....I'm sure there are a few people here who would like to know that.

 

[Jerry Clark H356 SV Persi]

I’ve just helped a boat neighbor repair his ill fitting and leaking connections to his waterheater on his Newly purchased 2002 Hunter 356. The previous owner mixed imperial and marine 15mm pex. It doesn’t work. He was running through water fast and kept hearing the “grunt” that is indicative of a leaking water system. We found his leaks at the fittings at the waterheater. Go buy the correct hose and whale fittings and save yourself a lot of grief.

 

[DayDreamer41]

Internal dimension is one measure, what is the comparison to the wall thicknesses between the two, this may be the difference.
Edit - A brief search show that 1/2" Pex has an O.D of 0.625" where a metric 16 mm has an O.D of 0.636" this could explain the misfit.