Remote Manifold for Radiant Heating


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Old 03-16-10, 02:40 PM
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Remote Manifold for Radiant Heating

We are completing a master bedroom addition with radiant floors (joist trak @8" OC) after running the calculations for heat load I've determined I need to supply 3.6 GPM to the manifold which is located about 60' away from my boiler (very difficult run as we do not have a basement to run the pipes through. I had thought about running 3/4" copper lines or 1" PEX lines for supply and return to the manifold, but given the difficulty of the run the thought occurred to me that I could run a set of 4 1/2" PEX lines for supply and another 4 for return, the flexibility of the 1/2" lines would make the installation a lot easier.
Has anyone done this before ? I am planing to put copper manifolds on each end to convert back to 1" piping which then would be connected to the actual radiant heat manifold.
The injection mixing will be done at the boiler side so the temp of the water being send to the remote of the manifold will only be around 120F

Does this make sense to anyone else or am I over complicating myself ?
Thanks for any suggestions
 
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Old 03-16-10, 03:45 PM
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since you want to limit your 1/2" pex runs to MAX 300 feet (250 being better), you end up eating 120 feet of pipe in the supply and return line. This will cost you in loops, ie. you will likely need to add a loop or two to compensate for the 120 feet lost in supply and return lines.
Make sense ?

Other than that there are no major drawbacks, unless its unconditioned space your going thru.
 
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Old 03-16-10, 04:13 PM
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TO, I'm not sure I understand what you are saying...

What I got from OP's post is that he is asking if it's OK to run four PARALLEL 1/2" Pex on each the supply and return sides, where they will be combined back into one, to feed the manifolds for the floor tubing.

So, I'm not sure how that relates to the 'extra loops' you mentioned?

Don, how did you figure the required 3.6 GPM you will need? I think that could be handled with a single 3/4", or a PAIR of 1/2"... no? (although, PEX is slightly smaller ID than copper, so you might need three runs...) Four runs of 1/2" sounds like overkill for that flow rate.
 
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Old 03-16-10, 08:58 PM
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NJ Trooper,
thank you for the reply, I've calculated my heat load to be approx 18000 BTU/hr thus giving me a required flow rate of 3.6 GPM. I calculated the head pressure of my parallel radiant loops and the common (supply and return ) piping given the required flow and anything smaller than 3/4" cooper would produce a head pressure > 14, thus my decision to go with quad 1/2" pex I think you're right I can probably get away with triple 1/2" ....
Would you consider this type of install with the parallel supply / return lines to be appropriate ?? or should I bite the bullet and run a single bigger line ?
The entire run will be inside conditioned space, but inside sofits, walls, etc making it very difficult to run a large size line. thanks again for any input.
 
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Old 03-16-10, 09:06 PM
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Ah well you know....

I guess I read to fast.

I would never run supply and return lines like that to a manifold, balancing would be a problem for sure,

Now, if your running a hot boiler anyways.. you could run a 1/2" supply and return line up to the room using high temp fluid and then use variable speed injection ( or a simple thermostatic zone valve) and mix down at the manifold.

At a 40 degree delta T your 18,000 BTU load would need .9 GPM
Easy for 1/2" pex

Oh and do yourself a favour and run PEX-AL
 
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Old 03-17-10, 09:26 AM
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TOHeating,
I was tempted to run the high temp water across but I do have 1 other low temp zone, its manifold is right next to the boiler and I am hoping to use a single injection system (and outdoor reset controller) to do both, I plan to use a tekmar 402 house controller to do the mixing, boiler control, etc.
Why would you recommend to use pex-al for the supply / return runs ?
Thanks for your help.
 
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Old 03-17-10, 11:56 AM
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I'm not sure where you are getting 3.6 gpm for 18,000 btu load. A 20f delta is 1.8 gpm and a 15f delta is 2.4 gpm.
What is the max flow through 1/2" pex from your manufacturer?
 
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Old 03-17-10, 04:16 PM
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PEX-AL has a much lower expansion ratio then normal PEX.
The supply and return lines will tend to creak as the temperature changes from room temp to target water temp.
ODR will help a bunch.
The Tn2 is a good choice of economical controls, you should have a good system.

Rbeck, I think he was planning a 10 degree dif on the slab. Lots of people seem to design it that way.
 
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Old 03-17-10, 08:01 PM
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Rbeck, I run the calculations using a 10F delta thus the 3.6 GPM. The rational behind running parallel 1/2" lines is to reduce the head pressure due to friction on the lines. Ideally a larger diameter pipe should be used but the run would be very difficult with 1" pex or 3/4" copper.
 
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Old 03-17-10, 08:05 PM
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TOheating,
thanks for the advice, I will plan to use Pex-al for the supply/return runs, the expansion is something that had me worried. It was a tough decision on the controls between the tekmar and the uponor multifunction, ultimately the indoor feedback and zone sync that the tekmar 402 offers tipped the scale. our boiler is quite a bit oversized and we tend to short cycle, i'm hoping the zone sync will help.
thanks again
 
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Old 03-18-10, 09:08 AM
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Use oxygen-barrier pex throughout the whole system.

FWIW, I would use the 3/4" or 1".
 
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Old 03-18-10, 09:21 PM
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Originally Posted by DonNando View Post
TOheating,
thanks for the advice, I will plan to use Pex-al for the supply/return runs, the expansion is something that had me worried. It was a tough decision on the controls between the tekmar and the uponor multifunction, ultimately the indoor feedback and zone sync that the tekmar 402 offers tipped the scale. our boiler is quite a bit oversized and we tend to short cycle, i'm hoping the zone sync will help.
thanks again
I also install the Uponor stuff, rather nice products. The thermostats are the cats.... well you know.

The system can be programmed with custom code, and therefore very flexible.

I do however think that Tekmar is still ahead in it's PID and zone load grouping. They tend to be more fuel conservative than comfort oriantated. They did miss the boat on user friendlyness.
 
 

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