Shower water pipe diameter

Hello,

for my overhead shower, the manufacturer requires a DN20 pipe for the water lines (hot and cold) (the shower arm has a 3/4'' connection). I measured the outer diameter of the installed plastic pipes; it is 20mm. I thought DN20 refers to the inner diameter. Could it be that only a DN15 pipe was installed? The installer claims that the DN20 pipe has a 20mm outer diameter.

Thank you very much for your help and best regards
Achim

The pipe is - as I have now found out - a Viega Sanfix 20mm PE-Xc pipe. Does that match the required DN20 connection for the rain shower (Hansgrohe Raindance Royale S350 Air)? I understand that pipe lengths, consumers, floor height, etc. come into play here - but what I don't understand as a layperson is why the installation manual then requires supply lines with DN20... :-?

Hello AMAG,
I am from Hansgrohe Service and found your inquiry here.
DN20 refers to the inner diameter (nominal diameter).
Whether the pipe installed on site is adequately sized, I cannot judge with 100% certainty, as the flow rate depends on many factors (geodetic height difference, pipe length ...etc.). The fact is that with this dimensioning, the flow velocity in this pipe section is higher.
If you have further questions, we are also happy to be available at the phone number 07836511282.
I hope this helps you and wish you a good day
Günther from the Service Team Hansgrohe