Pex tubing sizing?

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Old 11-21-16, 05:44 AM
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Pex tubing sizing?

I'd like to use Pex barrier for a new boiler install in my house. The existing lines to the convectors (not radiators) is 3/4" copper.

The maximum distance between the boiler and the convector furtherest from the boiler is about 35 feet.

Given there's an ID size difference between Pex 3/4" and copper 3/4" should I go with 1" Pex instead?

Any additional considerations about using Pex?

Thanks,

Craig L.
 
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Old 11-21-16, 06:52 AM
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I would ignore the difference in i.d. - go with 3/4" pex.

There is also a difference in i.d. between copper and steel pipe, but it is customarily ignored in selecting pipe sizes.
 
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Old 11-21-16, 06:56 AM
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I hope so.

I have a tendency to read one comment about such things and think that the world will come to an end and we'll freeze to death and I'll be blamed for the San Francisco earthquake(s) etc.

Most likely the "don't use this type of stuff...." is based on fellas using vise grips to crimp Pex SS rings.
 
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Old 11-21-16, 07:03 AM
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Also, 1" Pex will be more difficult to work with than 3/4",
 
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Old 11-21-16, 07:08 AM
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Not concerned about that- just want to make sure the Pex size is suitable for my system.
 
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Old 11-21-16, 07:14 AM
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3/4 PEX will be fine if you had 3/4 copper and performance was good.

Main consideration with using PEX for hydronic heating is allowing for the expansion and contraction so you don't get noise during warm up and cool down. Don't run through tight holes. Use the bushings and supports designed for PEX that allow the tubing to move without noise. A piece of larger size PEX makes good bushing for angled holes. Have some place in each run (usually at a bend) where there is a little excess tubing and room for a little more so as the length changes it doesn't pull or push on anything that doesn't move. For example, when running down a joist bay, you can switch the tubing from one side to the other and back again, leaving a little excess tubing in the bends (in other words, not pulling the tubing tight in the supports).
 
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Old 11-21-16, 07:27 AM
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Good idea for the bushings.

The Pex will be mounted on the bottom surface of the floor joists and not going through any of the joists. The tubing will not be clamped to the joists but rest on plywood (or Azek board) cross ties. The appearance of the whole system will look like railroad tracks- the "rails" being the Pex and the "ties" being the cross support pieces on the joist bottom edge.

Thanks for the help.

Craig
 
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