Helping a friend this afternoon to re route his first floor baseboard heating loop to accommodate a recent remodel. Is it allowable to use pex for this or do I need to stay with copper?

Yes, just be sure to use pex that has an oxygen barrier.

What's that mean? Are there different kinds of pex?

yes there are. for heating applications, it needs to have an inner foil oxygen barrier. It is referred to as Pex-Al-Pex

You also have to be aware that 3/4" PEX, which is what you will probably be using has about half the capacity of 3/4" copper tubing.

Thanks for the replies we got the job done with 3/4" copper. Better to stick with what you know when the job needs to get done..

Good Greif. Pex Does not have ½ the capacity of copper. That’s yet another plumbing myth. I don’t mean to cloud this up with facts but others might read that and take it as the truth. There IS a reduction in capacity though. I submit that the reduction for heating applications does not matter at all.

Here are some numbers. (Looked up, not guessed at) Pex is the material of choice for radiant floor heating systems other than the near boiler piping and that is where people want to have everything secured well and looking neat. The distribution piping is also normally PEX to the manifolds in these systems by folks who know what they are doing. (Less 90’s = less pressure drop and much better insulation qualities, quieter systems, etc, etc.)

¾” copper at 5fps flow rate = 7.6gpm
(Over the recommended 4FPS given by the national copper pipe Inst numbers are from Copper.org due to erosion and noise!)

¾” Pex at 5.5fps flow rate (Did not have 5fps listed) = 6gpm (That’s about 78% not 50%)

CPVC ¾” @ 5FPS = 7 gpm

Notes:
1. These numbers represent straight tubing and NO BENDS or other system losses which are greater with systems requiring more 90*s like copper and cpvc.

2. Most Baseboard systems are grossly oversized anyway.

3. 02 barrier PEX is also available in Rehau and Uponor

4. Pex is available in PEXa, PEXb, PEXc and PEX-AL-PEX. A, b, c, is kind of like K, L, M copper. A is more flexible and stronger than the others not including Pex-al-pex which is just as strong just a lot more stiff.

5. In reality, flows through our systems are much lower than you may think anyway.

6. 100’ of ¾”cpvc holds 2.04 gallons of water, ¾” copper holds 2.51 gallons. (could not find PEX) There is about a 20% difference there.

Copper is great stuff. If you like it and can afford it then by all means go with it. There are other viable options though. If you don’t know what you are doing, copper may actually be MORE forgiving since it is more “structural” than the plastics. (Assuming you can solder well)

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Give your kids a great start on the future! Encourage them learn a trade. Even if they go on to do other things, it's always nice to know that they have something to fall back on. Call your local technical training center or trade school to learn more.

There is one factor you omitted in your data...pressure loss over the length of a pipe. This may be less important in a pumped heating system, than in the domestic water system.

It can be MORE important, since it is a function of velocity, and a heating pump, if it is oversized, can develop high velocities.

pex al pex is a compositepipe made of an aluminumtube laminatedto interior and exteriorlayers of cross linked polyethelene rated at 125 psi @180 0F

Don .Glad to hear you keep the copper job copper.never any reason to deflect from the best tubing for the job.