PEX ID - What determins the usable ID in a system?

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Old 10-07-14, 02:24 PM
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PEX ID - What determins the usable ID in a system?

I want to use PEX to get heat from my basement to a second floor addition.

I was going to purchase 3/4" OD PEX but I am concerned that the ID is only 0.671" and the fittings ID is only about .5"

Most of the run will be 3/4" copper, with a 10' PEX supply and return line run in a wall.

How do I know if the limited ID of the PEX Pipe and the PEX Fittings will be okay?

Is it determined by the circulator?
 
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Old 10-07-14, 03:30 PM
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If using PEX line and PEX fittings and PEX rings, and PEX crimper, you are in the right boat. If you are asking about the amount of water being run through the fittings, it won't affect potable water, but heating, I'll have to let one of the HVAC guys answer that.
 
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Old 10-07-14, 03:46 PM
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head loss per 100 feet of run.
generally, pex replaces copper. It does have a smaller ID then copper, but the fact that you tend not to use mechanical fittings in the pipework keep the head loss near that of a system with copper and a bunch of mechanical fittings in it.
 
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Old 10-07-14, 03:49 PM
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Not a problem. The two 10' pex sections plus the fittings will not cause very significant pressure drop. But, be sure to use pex with an oxygen barrier - important.

Flow through pipes of different ID's isn't like shelled corn through two different sized strainers in series - where the smallest controls.
 
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Old 10-07-14, 04:06 PM
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isn't like shelled corn through two different sized strainers in series
Spoken like a true Iowan!

To directly answer the question of what controls...

My answer would be VELOCITY of the flow. Use too small of a pipe/tube and you have to speed the water through the system... may be noisy, can cause internal pipe erosion.

I would ask you how many square feet you are heating, what the heat loss for the area is...
 
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Old 10-07-14, 04:35 PM
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Spoken like a true Iowan!
No, I should have said cracked corn through two sieves. I'm a (little-) town-boy, but I grew up with some future farmers.
 
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Old 10-07-14, 06:46 PM
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Coulda left it at that and I woulda never known!

I spent a week in Dubuque one day but that's as far west I ever been.

I do know tabacky though!
 
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Old 10-09-14, 09:57 AM
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The room is 293 sqft. There will be a copper run of about 34' (from the boiler) to a PEX run of about 10' (up to the 2nd floor) to a copper run of about 40' (20' of which are finned baseboard) to another 10' PEX run (back down wall to basement) and then a copper run of 34' (back to the boiler).

So far the heat-loss calculations have eluded me, but I am working on them.

29.23 sqft of windows, 1 wall 245" external, 2 walls 173" external, 90" ceiling, standard insulation, heated area below.

Also, using a TACO 007-F5 circulator, dedicated to just this loop.
 

Last edited by syd81; 10-09-14 at 10:14 AM.
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Old 10-09-14, 01:02 PM
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That should be fine Syd... 20' of baseboard you only need to flow a couple GPM...
 
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