More pex loops better???
 

I'm putting hydronic pex heating in a high mass concrete slab 14' x 30'. It is for an open room floor plan so it could easily be done with just two loops and meet 1/2 pex length recommendations(approx two 200' loops) spaced from 6" apart near exterior to 12" in the interior. But would increasing number of and shortening the length be better for supplying more and quicker heating if needed(worst case demand). It certainly wouldn't over complicate the system to have 3 or 4 loops in the manifold to any great cost. Structure is super insulated to R50 walls and R80 ceilings. and all the details of Hi-R construction built into the design. Once the slab is poured its too late for any should have's, lol.

The closer the PEX runs, the more efficient it will be.

Old School Amreican rule of thumb is 12" spacing; from my research, Northern Europeans favor closer spacings, with 6" not being unusual. European energy is much more expensive than ours is now.

Sounds like you have a handle on PEX run lengths, and headers, etc.

I'd advise closer PEX runs, similar to the Northern European practice.

You are right about quicker temperature increase, but temperature decrease will be no different.

The real benefit to you will be lower fuel cost over the life of your system.

Hope this helps.

Regards,

-AC_Hacker

Decided to go with three shorter loops because my local Menard's store was clearing out 250' rolls of 1/2 of non-O2 pex 75% off to go to 300' rolls. I have three 200' runs in the layout plan now so no splices and Big savings. Most manifolds I've seen start at three anyway and about same as two price.

6" is more or less "old school" overhere in the Netherlands. 4" (or even less!!) is favourable, especially when you are using a heatpump. Or if you are planning to use one in the future.
More tubelength (so closer tubing), means lower watertemperature for the same amount of heat.
And lower watertemperature means a more efficient heatpump.
The difference in e-consumption is about 2,5% per °C.
So if you ar planning a hydronic heating right now, please do it right the first time.....

Drake, I'm with you. I think some of the responses were thinking you were talking about spacing between the pipes, but I think you were talking about the length of the run.

Shorter runs will give you a warmer temperature at the return, so should heat everything more uniformly and more quickly. Heck, if you piped it that way and poured the slab, then decided later that you wanted fewer, longer runs, you could series connect a couple of runs at the manifold location. You could probably even valve it such that you could switch on a whim.

Radiantec is a good site to look at radiant heating systems.