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PEX (polyethylene) pipe etc...?

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Posted by john on September 1, 2008, 12:04 am
Went to the local "Lowes Depot" today to get some piping for the radiant
part of the solar heating system.  The specs on the pipe says it is
suitable for radiant heating but two lines later says only good to 140F.
  Any one used this stuff for their solar heating system.  I already
melted a piece of the rigid PVC (may have been CPVC) while testing the
panels in the yard.  Even if it handles the heat short term,  will it
get brittle as it ages?

Same questions for the polyethylene tanks, they say rated only to 140F
for short periods.  I am finding reasonably priced polyethylene tanks
everywhere, the polypropylene are few, far between, and are quite
pricey.  Any idea if or how much the heat shortens the life span of the
tank or polyethylene in general?


Posted by AstickfortheMULE on September 1, 2008, 3:37 am

I use PEX for both supply and return to my solar panels but I have a
large unglazed system called energie Solaire.  My storage is large and
does not really get above $80deg in the summer.

Wirsbo claims to have  a section of pex pipe under something like 120
psi with a temperature of 203deg F continuously for 30 years.

No problems with mine so far.

Having said that, I would just copper. The pex gets very soft and
expands quite a bit.  PVC will fail and so will CPVC.

I would not consider straight PE for your storage.  That will fail as

Consider welding your own tank or do what I did, you will be hard
pressed to beat the price and doubt the performance.

I can not say enough good things about this tank and ships 20" wide
and  can slip in door ways as it is collapsable.



Posted by john on September 2, 2008, 4:51 am

Thanks for the reply.  What issues would I encounter with CPVC; that's
supposed to be good to 200F.  I intend to use CPVC for the underfloor
radiant heating part of the system in the shed as well.  Also intend to
use a good length of copper on the discharge side of the collector array
to protect the plastic from inadvertent steam.

After I posted, I found some back posts on this same subject.  After
reading that and the mfg's label, I am a little hesitant to use PEX for
anything or at least the PEX in the local Lowes Depot stores.


AstickfortheMULE wrote:

Posted by AstickfortheMULE on September 2, 2008, 3:59 pm
 Turns out all pex is not created equal.

Don't use CPVC for radiant, that is not a good idea.  Is it in the
concrete? or staple up?

1/2" pex is probably closer to 20 cents a  foot so it is plenty cheap.

I have tried to go cheap in the past and you just end up re doing it
or causing more problems in the future.

You will never find boiler guy or HVAC use anything other than copper.
After you factor in labobor and failure and damage, It is the cheapest
thing out there.

I used 1" pex on discharge because I tried to remove it from a
concrete wall and with a 2000 deg F torch down the middle for 30
minutes, it still would not budge until I put a come along on it with
about 2000 lbs of extraction force.

I am impressed with WIRSBO brand.

The stuff at Lowes is probably not the same quality.  The WIRSBO
fittings are dynamite as well.

Like I said,  203 deg F with 120PSI for 25 years continuously.  Look
it up.

Good luck


Posted by john on September 3, 2008, 1:02 am

AstickfortheMULE wrote:

It wouldn't be in a concrete floor, it's in a greenhouse that has a wood
chip floor (needed cheap, light weight backfill...)  The heater design
is still in constant flux.  One of the things I am trying to find out is
where to put the radiant pipe to get it out of the way.  Once I take the
coils out of the floor I start to use the limited space in the
greenhouse and suddenly I am back to forced air (have a coil for that
already.) I just like the idea of passive; it is less complicated once
installed or so I think...

Just for future reference, what is the issue with CPVC?  Granted, if I
was encasing something in concrete it would have to be proven.  Do you
have problems with CPVC when it is accessible or just when it is sealed
forever in concrete?

Since the greenhouse will be literally wall to wall plants, I could just
lay the pex around the pots (as was suggested on another forum) to heat
the plants.  Even the cheap stuff I saw in the store seemed durable and

Same here, that's one of the reasons I posted, to gain from the
knowledge and experience of others.

I'm partial to copper myself, just that lately I think it comes from oil
wells in Saudi Arabia with gold and diamonds produced as byproducts...
No more area than I have, it may not cost that much to put copper in the
greenhouse, I just do not know yet how to figure the piping load, flow,
design, etc..  The copper would definitely transfer heat more
efficiently.  The 100' run from the tank to the panels is what is going
to cost if I have to use copper.  The panels have 1" fittings on them
and I don't know a good enough reason to down size the pipe any less
than 1"..

I did find an "IPEX" brand that is supposed to be good for higher
temperatures (on line), I am going to check out some of the local
plumbing stores for one of these two brands.  I started with Lowes Depot
(I can't tell these two stores apart unless I read the sign...) because
they are open when I am off from work.

Do you thermally insulate your PEX?

That is impressive, I will definitely check into it.  BTW, why such a
high pressure?

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