Laying out pex tubing for in-floor heating

[Sedgehammer]

I had this in 2 houses. It was so fantastic that i've decided to put it in our barn build. i did not plan and layout my other houses. i was so busy i hired it. i been looking at some online layout tools and they are asking for lots of inputs that I don't know. are those important or can one just lay it out with the 6" rule near doors and 12" spacing there after?

[doc henderson]

for one big room that is fine.  the trick is keeping all runs in a one zone(on one set of manifolds) the same length and not making splices under the slab, and not crossing over other tubing.  also the lengths of each tube has to fall into a sweet spot for resistance based on the diameter of the tubing.  IE not one tube dong the whole floor.  my shop floor had 6 length of tubing for one zone.  my shop has 3 zones overall, but I just have them all gong to one thermostat.  a well planned pattern is nice if you ever need to put a hole in the floor without damaging the pex.  I used 1/4 inch graph paper to lay it out to scale.

[azmtnman]

I can't help with your layout. However, I had to completely replumb our house. I got everything from these folks:
PexUniverse - PEX, Plumbing, Heating, HVAC Supplies
A live person even called me on my 1st order because my billing address and shipping address are different. They have pex (you use oxygen barrier pex for heating) in 500' rolls and everything is very reasonably--even the cheapest--priced (less than 1/2 of the big box stores.)
Just FYI. 

[Bandmill Bandit]

IF you want to PM me ill send you my phone number and we can chat. i have done a few barns, shops and 3 houses over the last 20 years.

it pretty simple really BUT there are different ways to do things for different reason and applications.

[Thomasjw4]

I can tell you to price the barrier pex on Amazon.   You can get it ALOT cheaper. 

[moosehunter]

I used supply house . com. for all my supplies. Good people. 
A plumber friend gave me this book. Lots of great info. I did all 300' loops. System works great.


 
mh

[scsmith42]

Lots of good advice in this thread thus far.

My 5,300 ft shop has 3 zones, and the entire building utilizes 300' runs.  Material was sourced from local plumbing houses, Radiantec, and e-bay.  

Key things that I learned.

1 - insulate under the slab!  Thick sheets of EPS or Styrofoam are best.
2 - Insulate the perimeter of the slab!  Otherwise you will lose heat through the edges.
3 - Where the tubes emanate from the slab, run them through plastic sleeves or foam.  I used long radius PVC conduit elbows to run my 1/2" pex inside of.

The best price for fittings and manifolds was e-bay.  I used Radiantec for the pumps.  Radiantec also has some great information on their website about system design, do's and don'ts.

My shop runs are all 300'.  The perimeter starts at 6" centers (inside of the outer walls), then jumps 6" per loop until I'm at 24".  The main shop area is 24".  There are no splices in the concrete.

The photo below shows the pex tubes installed before the concrete pour.  They are installed below the slab bolsters / reinforcing mesh of the 6" thick slab.



 

This photo shows the manifolds, pumps and above-floor connections.  All of the pex runs are valved on the discharge side.  The two runs that are not hooked up on the left side of the photo are for future runs to a log cabin that is adjacent to my shop.



 

[Sedgehammer]

@scsmith42 Your mechanical room looked very neatly done. I'm planning something similar to what you sis there, but a little more compact

Never seen, nor heard of going 2' oc for spacing, but if it works, great. we'll do 6" against the walls, then 12'. might stretch some interior stuff to 18" if need be

Have 15 psi eps going under the slab. I think it's 8.8 r value. In the 7" thick slab will run the pex on top of the re-bar. will use pex-al-pex for the 4" crete. will run on the eps

4 zones under slab. main shop area will be 3 coils of 300' looks like. kitchen eating area is 3 of 175' i think

will use a gas fired boiler with domestic

I am using multiple searches looking for the best deals on everything. No way will buy from one place @Thomasjw4  and there are places cheaper than amzonian

Thanks for the book info @moosehunter 

Might take you up on that @Bandmill Bandit i'll know more in the coming week, thanks

[Don P]

Running it deep in the pour is less efficient and slower response than running it shallow... within reason.

[Sedgehammer]

Running it deep in the pour is less efficient and slower response than running it shallow... within reason.

correct. that's why it'll be on top of the rebar in the thicker crete, but will have to go under the rebar in the 4" pour. leastwise i see no way of putting it higher in the 4"

[PoginyHill]

Running it deep in the pour is less efficient and slower response than running it shallow... within reason.

correct. that's why it'll be on top of the rebar in the thicker crete, but will have to go under the rebar in the 4" pour. leastwise i see no way of putting it higher in the 4"

Having PEX deeper won't impact efficiency (what percent of boiler heat input makes it into the room) so much as reducing BTU/hr capacity and response time. With good insulation below the slab, where the pipe is in the slab won't impact heat loss to any great extent. But maybe we're just talking semantics.

[Sedgehammer]

it does according to a study done I read a while back. 2" vs 3" isn't much neither is 3" to 4", but 2" vs 4" is a fair amount, but even that isn't a huge amount. But putting it at the bottom of 7" pour wood be a fair amount.

[PoginyHill]

I agree there is some impact. And I've not read any specifics as far as numbers or magnitude. From a heat transfer point-of-view, the impact is the rate of heat transfer through concrete versus the heat transfer rate through the insulation. So the better the insulation below the slab, the less the impact of PEX placement. We are splitting hairs here, but I'm a bit of a geek with heat transfer and thermodynamic stuff.

[scsmith42]

Running it deep in the pour is less efficient and slower response than running it shallow... within reason.

I don't disagree.  In my instance, my logic was that I wanted the wire reinforcement in the lower 1/3 of the slab for the best tensile reinforcement, and I also wanted to be able to drill to a depth of 3-1/2" anywhere in the slab in order to set anchors.  So that meant that the reinforcing wire would be 4" down from the top of the slab.
By placing the pex tubing below the wire and at 4" depth from the top of the tubing to the slab surface, I am able install anchors anywhere in my slab and not have to worry about hitting a pex run.