PEX
is an acronym for polyethylene, crosslinked. It is made to last about 200 years, but if you live for
another 200 years and the PEX you buy is still in the floor and working as we know it will -
please give us a call - as soon as possible.
PEX pipe is, however, the material you'll find all over Europe. The Europeans have been doing
hydronic radiant floor heating with PEX since the early Seventies and there's a lot more of it
there than there is here. PEX Tubing has a great track record.
PEX Tubing manufacturers have been taking the time to
spell out the differences between their products. And there are
differences in the way different companies make PEX piping. Knowing this can
help you make the right decision when you're shopping for a PEX supplier for your radiant floor
heating or plumbing system.
Most manufacturers start with a material called HDPE,
which stands for High-Density Polyethylene. HDPE evolved from polyethylene, a
material discovered by accident by a group of British scientists during the 1930s.
PEX differs from HDPE in that PEX has this special
three-dimensional link between the molecules. It's this network of macromolecules that gives
PEX such a fine memory for its original shape. If you kink PEX pipe,
you can just heat it up and it will always return to the shape in which it was first crosslinked.
The linking of the molecules happens during the manufacturing
process, and how a manufacturer chooses to make that happen affects
the properties of the final product. The manufacturer can't link all
the molecules together because that would make the PEX pipe too brittle. On
the other hand, if they link too few molecules the material won't be
any better than HDPE, from whence it came. They have to find just the
right combination of linked and non-linked molecules.
There are different ways to get where they need to go, and from
what I've learned, some ways seem better than others. Here are the
principal methods manufacturers are using today to make PEX:
Engel-method PEX (also known as PEX-A) This is the stuff Tomas
Engel brought into the world. Engel was the guy who invented PEX. He is a European scientist and he
had nothing to do with the
radiant heating industry when he invented PEX. What's important for you to know is
that Engel-method PEX gets crosslinked while it's still in its melted
form. The manufacturers do this by adding peroxide to the mix and then
applying a tremendous amount of pressure and temperature to the
liquid. What comes squirting out of the machine is PEX that's as clear as
glass. As it cools, it takes on a darker color. The Engel method gives
the pipe an essentially uniform distribution of the crosslinking sites
throughout the material. This is the best way to make PEX pipe.
It takes a while longer to do it this way, and this sort of PEX may
cost a bit more.
HousePEX PEX-A Tubing is made with the Engle-Method - thus HousePEX PEX-A
PEX is "PEX-A".
Irradiation-method PEX (also known as PEX-C) Irradiated
PEX starts out as straight
polyethylene tubing. As with other methods of making straight
polyethylene, the tubing takes on a definite form during the extrusion
process. With the irradiation method, the crosslinking takes place in
a second process when the manufacturer runs the tubing through an
electron beam cannon. The beam gets the polyethylene molecules so
excited that they crosslink. This method can sometimes result in a less uniform crosslinking of
the material. If it's not done properly, the outer layer of
irradiated PEX tube can become brittle, but this is not a concern in a
well-controlled process.
HousePEX PEX-C Tubing is made with the Irradiation-method - thus HousePEX PEX-C
PEX is "PEX-C".
Silane-method PEX (also known as PEX-B) The big
difference between this method and the other two methods is that with the Engel and
Irradiation methods, the crosslinking consists of a bond between
carbon molecules. With the Silane method the crosslinking takes place
across silicon and oxygen molecules. These links are weaker than the
carbon-carbon links that result from the other methods, and this may
have an effect on the long-term chemical stability of the material. If
we live long enough, we'll probably find out.
It's good for you to know the differences between these materials even
though they all go under the name PEX. Let's face it, you're the one
who's going to be putting the tubing under the floor.
In fairness, though, I have to tell you that none of these methods
is a bad method; The American Society for Testing and Materials (ASTM)
approves all three methods. However, in a world among
"equals," it seems to me that some methods are more
"equal" than others. Don't think of PEX as a commodity item.
There is a difference.
And this is why HouseNeeds sells
PEX Tubing manufactured with the Engel-method for radiant heat for floors, walls, and
ceilings as well as your plumbing needs.
We strive to offer only the best products for your housing needs.
Text on this page is taken from page 88 in Dan Holohans book, Hydronic Radiant Heating
available here:
Books on Radiant Heating
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