PEX vs AL-PEX

[rockycmt]

I have been planning a copper to PEX conversion for my hydronic monoflow loop via a PEX manifold. I read I have to use AL-PEX to prevent AIR from penetrating.

First...How does Air penetrate PEX to begin with?
Second...Do I need to do this? I am putting on an air eliminator.

[jadnashua]

You want a pex rated for hydronic use AND it should have an oxygen barrier. The specific version you choose is up to you. O2 can diffuse through the tubing wall if it doesn't have the barrier. An air eliminator only extracts bubbles, not dissolved O2. Dissolved O2 will react with the metals (especially iron) in the system (like the body and maybe impeller of the circulating pump). This isn't an issue with potable water, but can be critical in a closed system.

[BadgerBoilerMN]

All PEX tubing must conform to DIN 4726, a standard established by the German institute for standards. Any PEX tubing meeting this German standard is adequate for all residential hydronic heating systems. The PEX-AL-PEX radiant tubing meets and exceeds this standard since in is in fact a tube of aluminum sandwiched between the layers of PEX. This makes the tube more rigid and expensive. There are reasons to use it as the stiffness lends itself to some applications better than others and in can be had in 20' straight sticks and rolls (all other PEX available in rolls only).

Unless you have a special requirement the standard PEX will do.


We use various PEX products here in Minneapolis when removing low hanging boiler piping to allow for basement remodels, and installing sub-floor radiant heating. We install PEX-AL-PEX when high temperatures or the rigid self-supporting qualities are needed.

But I wonder why you want to take out your mono-flo system?

[rockycmt]

I am doing a basement remodel. I want to lift everything up into the rafters. Also make proper zones to support living vs bedroom space. Right now whole house is on one monoflow loop. I plan to have 4 zones with 4 pumps. 1 living space, 1 bedrooms first floor, 1 bedrooms second floor, one indirect HW with priority. This seems like a much better setup. And inexpensive to do. Pumps, manifold, and controler with PEX < 1K.

[rockycmt]

One of the reasons I asked this question is I seen that AL-PEX is a totally different animal to work with. Can not use the same tools and fittings. Is there an equivalent PEX with O2 barrier product that I can use my standard crip rings on?

[jadnashua]

Most any pex designed for hydronic heating should work. FWIW, breaking the house up into four zones might make for problems. Since the heat load when only one zone is calling for heat will be fairly small, your boiler might short-cycle itself to death without making some other changes since it will be producing much more heat than can be absorbed by the single zone (and maybe all zones, since the tendency is to overbuy capacity).