Questions on Pex Piping

Old 10-08-04, 03:05 PM
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Questions on Pex Piping

Question about Pex Piping.

1) Why can't you use PEX like normal copper piping and daisy chain it everywhere?

2) When you put in a manifold and run the pipe (separately) to each appliance, is the pipe generally a smaller diameter than classic copper daisy chains? Ie Suppose I have 3/4" running everywhere in copper. If I switch to PEX, do I stick with the same 3/4" line to each appliance or do I reduce it to 1/2" or 3/8"?

3) I thought I read somewhere that PEX has a smaller inside diameter than copper of the same size. How big of a difference is there? Ie does a 1" PEX pipe have the same inside diameter of a 3/4" copper pipe? So in my case, if I want to use 3/4" lines, would you suggest using 3/4" PEX or going up to 1" PEX?

4) I haven't read anything on PEX about fire rating. The reason I ask this is that copper pipe has a melting point just over 1000 degrees. I haven't been able to find out what the melting point of PEX is yet, although it states not to use it if the water is greater than 200 degrees at 80 psi. I guess I am just worried about the PEX pipe bursting. Ie I have a small kitchen fire that can easily be put out with a fire extinguisher. I don't want to have to worry about the pipes behind the walls heating up and bursting on me.

Any thoughts?
Old 10-08-04, 04:49 PM
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1. You can if allowed by code, here we use it everywhere.

2. If from a manifold, you can run 3/4" or 1/2", rule of thumb, no more then two fixtures on one 1/2" line. At the fixture reduce to 3/8" supplies.

3. The ID inside pex is the same as copper, the fitting do infact reduce and there is no noticeable difference.

4. A water heater will trip the T&P valve at 210 degrees, you will learn if the heater is too hot probably long before it effects the pipes.

Pex is a good system, unlike its predecessor quest, it has a 25 year warranty. We use is widely here in Oregon, never seen on the news yet that there was a major disaster do to it.

Not to worry if you use it, be ensured nothing is bad about it.

PEX For More Info Click Here

Last edited by Plumber2000; 10-08-04 at 05:31 PM.
Old 10-13-04, 09:51 AM
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1) Most people consider having "home runs" a big advantage of PEX pipe. Your able to isolate any fixture in the house from the header station. Makes for really easy repair work. Much less confusing this way as well.

2) Already answered, but yes.

3) Already answered

4) PEX has a pretty low melting point. If you install it too close to light fixtures, you can run the risk of melting thru it.

However, a small fire as you describe would never be enough to melt it I'm sure. And if the fire IS big enough to melt it, broken plastic pipe will the be least of your worries. Actually, if it did melt it, it's easy to fix (that's one of its advantages) so it wouldn't be a big deal at all.

To be picky...bursting would never be an issue with heating pipes...melting would

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