Some performance data specs on logstor underground lines and recommended flow rates
http://www.urecon.com/applications/hydronics_flexible.htmlFlow rates and erosion velocity,
http://www.urecon.com/documents/pdfs/other/PEXFlex_losstable.pdf90's, backside of Tee, iron pipe shoulder nipple threads and IP threads are where I see the most erosion failures from excessive flow. In lower temp applications below 160, some use cpvc to counter the growing costs of brass and copper, especially for header runs on snow melt applications.
Pipe size. Max flow. BTU/hr@DT20
1/2" copper = 1.5gpm 15kbtuh
3/4. ". 4gpm. 40kbtuh
1". 8gpm. 80kbtuh
1.25". 14gpm. 140kbtuh
1.5". 22gpm. 220kbtuh
2". 44gpm. 440kbtuh
3/8 pex. .6gpm. 6kbtuh
1/2". 1.5gpm. 15kbtuh. Note pex brand and specs differ. For ID.
5/8". 2.4gpm. 24kbtuh. Head loss and flow rates.
3/4". 3.2gpm. 32kbtuh. Uponor, viega, stadler are full IPS diameter
1". Pex. 5.4gpm. 54kbtuh. And their fittings
1.25". 8gpm. 80kbtuh
1.5". 11.2gpm. 112kbtuh
2" pex. 20gpm. 200kbtuh
Pressure
28" of water = 1psi of static head. 23.33'= 10psi
Strap on temp gauges are a very cheap and effective troubleshooting tool, so are IR guns once you've learned how to get consistent accurate measurements.
Another flow rate chart by Taco, includes pex-Al-pex and fitting head loss values
http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf