Foam Insulated PEX
Pex Tubing
Standard size pex tubing is manufactured to SDR9 standards which is the same outside diameter as copper pipe but has a wall thickness 1/9th the diameter. If you see something advertised like "true 1 inch" or "Not 1 inch OD like others" it is actually metric size. The pipe listed above as 1" ID is 32mm OD and is manufacturered SDR11 standards. This is 1.032" ID which is very close to standard 1-1/4" pex (1.054" ID) but the thinner pex wall allows for more insulation. NB= Non Oxygen Barrier Pex OB= Oxygen Barrier Pex OB usually isn't required unless you are running a pressurized system with no chemicals. It never hurts to use OB pex on an open system (open system has overflow tube at boiler) but is usually just a waste of money and doesn't make any difference.
NOTE: --------------------------------------------------------------------------------------------------------------------------------------------- Pex-Al-Pex Tubing Pex-al-pex is sold as inside diameter instead of copper tube size. It has a few advantages over normal pex. It doesn't expand in length so if you have an installation that can not allow for expansion when the pex gets hot you may want to consider it. Also the sizes fall between pex so it is also a good alternative if you need something a little bigger than 1" pex.
PEX-AL-PEX is made with an exterior layer of PEX then adhesive followed by a layer of aluminum, another layer of adhesive and finally a layer of PEX. The aluminum acts as an oxygen barrier so all PAP tubing is considered OB.
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