PEX in the garage attic?

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Old 03-13-18, 07:43 PM
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PEX in the garage attic?

I DIY replaced cold water copper with PVC and CPVC. I live in Florida and garage attic gets very hot in the summer. Currently, I have 3/4" PVC covered with foam insulation in the attic that replaced the 3/4" copper main under the slab. I would like to replace this PVC with 3/4" PEX. But PEX pressure rating is not as high as PVC. At 110 F, 3/4" PVC has 200+ psi, whereas PEX has about 100 psi. Is it safe to use PEX in hot attic with foam insulation?

A related question:
Is there a trade secret or knowhow how to run 10' pipe that cannot be clamped every 3' to 4'? The space is between the first and second floor, wide but shallow for me to crawl. Can I clamp the pipe on a long 2x2 and pre-apply wood glue to the 2x2?
 
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Old 03-14-18, 02:46 AM
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I'm not sure where you are getting those numbers...but then no plumbing pro. Looks to me like PEX is good for 100PSI at 180 degrees. If your attic is getting that warm, I think you have other issues to worry about. And if your pressure is anywhere near that high, you need a pressure regulating/reducing valve set to about 60 psi.
 
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Old 03-14-18, 06:04 AM
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I live in So. FL and used PEX in the bathroom remodel I did and fully inspected. The PEX runs straight up into the attic for the rain shower and to reach the second shower head... no problems. I used ProPEX, picked up an expansion tool on eBay ahd sold it for the same price when I was done.
 
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Old 03-14-18, 06:07 AM
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There are two things you need to watch with PEX.

1. It is NOT UV resistant. If any light can shine into your attic through vents or windows then you need to protect the PEX inside something like foam pipe insulation or otherwise shield it from all sunlight.

2. Sharp metal can cut PEX. It must be routed so no sharp nail points or steel truss brackets can touch the PEX. Pex can tolerate not being supported. It will just sag and lay without harm but it cannot touch anything sharp. The minute movement of the pipe when you turn water on and off can cause sharp objects to cut the PEX.
 
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Old 03-14-18, 11:44 AM
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Thank you for the notes.
Good to know PEX can be used in the attic. I am going to cover PEX with foam insulation. In hot summer days, I have 90 deg F water coming out of cold water faucet initially. So I doubt attic temperature reaches 180 deg F. Maybe 120-130 F. No light inside the attic.

One thing I noticed from DIY replumbing. Unsupported run of pipe seems to increase water hammer. Unless someone suggests a better tip, I will clamp PEX on 2x2 and glue it on joists.

I suppose ProPEX is a brand for PEX tools. But when would I need an expansion tool?
 
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Old 03-14-18, 01:21 PM
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I actually think unsupported runs of PEX reduce water hammer as the pipe is able to flex and absorb the shock of the water hammer affect.
 
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Old 03-15-18, 07:29 AM
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Thank you. It will be my first project with PEX.
 
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Old 03-15-18, 05:51 PM
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There are a number of different PEX installation methods, all seem to work reliably. I bought a crimping tool for about $100 and it uses copper crimps to make the connections. Best tool investment I've ever made.
The expansion fittings do the same thing, but secure the pipe to the fittings differently. I'd see what your local hardware store or big box store carries and go that way.

I don't see any issue with the 2x2 idea. If it were me, I'd probably use a 2x4 and screw/nail it down. Wood glue won't really do anything - maybe construction adhesive (Liquid Nails) would work, but it seems like a pain. I also don't see any big issue with leaving it hanging free in that 10' of space that you can't reach.
 
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Old 03-16-18, 09:33 AM
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Thank you for the confirmation. I plan to do this next weekend.
 
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