scaling copper to pex

Georg

Is it correct that I need 2 times the feet of head for 3/4'' pex than for 3/4'' copper?

If I understand the system curve correctly, the required head decreases with the pipe area squared, or the diameter to the power of 4. I measured the inner diameter of copper-M to be about 13/16'', whereas 3/4 pex only has 11/16''. And (13/11)^4 is approximately 2.

Is the difference between pex and copper really that large?

Timco

Check the ID of the pex fittings...waaay less than the pipe...Wirsbo expands, but standard crimp pex ftgs are the same ID as one size smaller copper...or slightly less.

Tim

Steve Ebels_3

To a certain point

That's correct. But, a typical pex run will have virtually no fittings which add considerably on the copper side. When using pex you're usually dealing with what amounts to a straight run of tube.