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Discussion Starter · #1 ·
Hey guys, how many inchs do you guys leave for the spacing between the pex tubing for on top of floor heating? The pex is 3/8. Thanks
 

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KemoSabe
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Hey guys, how many inchs do you guys leave for the spacing between the pex tubing for on top of floor heating? The pex is 3/8. Thanks
We never put tubing down without having load calcs done and specific drawings giving spacing, length of loop, flow rate and water temp.
 

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Discussion Starter · #3 ·
Thanks was just curious. Figured it would be difficult to answer without more demensions. Do you usually space it closer in a concrete basement slap then you would on top of plywood?
 

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Discussion Starter · #5 ·
Oh ok thanks just had it installed and it is about 11 inches apart. Thought that was kinda wide. They are all small rooms. Hopefully all works out.. Thank you
 

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Oh ok thanks just had it installed and it is about 11 inches apart. Thought that was kinda wide. They are all small rooms. Hopefully all works out.. Thank you

8" is a guidline i use, many factors play in, heat loss, floor type, water temp, etc... also the feed should be run along outside wall, I am pretty sure you will be fine. The spacing and radiant in general is pretty forgiving, GMOD
 

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KemoSabe
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Thanks was just curious. Figured it would be difficult to answer without more demensions. Do you usually space it closer in a concrete basement slap then you would on top of plywood?
In the applications that I've been involved with, there is usually closer spacing along outside walls, due the fact that there is a heavier load. 6" spacing for at least the first 2 or 3 passes, then 12" centers for the remainder, although there have been a few cases where 9" was speced.

There wasn't a difference in spacing being poured in a 4" slab or on top of plywood with 1 1/2" Gypcrete pour. The floor heats pretty evenly and once up to temperature, radiates as one solid mass. The water temp and flow rate is surprisingly low compared to what I expected, which is probably why it heats so evenly, with no noticable "hot spots".
 

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Discussion Starter · #8 ·
Thanks first time im seeing it installed. Looks awesome the way you guys install it. Funny thing is everytime I talk about it to people outside the construction business they think its something new..
 

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Thanks first time im seeing it installed. Looks awesome the way you guys install it. Funny thing is everytime I talk about it to people outside the construction business they think its something new..
Very old technology, Hicksville all the levitt houses from the 40'S used radiant, copper tubes that mostly started to get replaced in the 80,s due to failiure, i am expecting the PEX to last much longer, GMOD
 

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Discussion Starter · #10 ·
Seems it would be alot more work doing it with copper. Pex really is awesome stuff to bad they dont let you use it for hot and cold water in nyc.
 

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Did a huge radiant job about 5 years back. I had precise length and spacing requirements for each room calculated by an engineer. I would never attempt a large job without someone doing the heat load/ loss calcs.
 

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On 1/2 inch, what would be the maximum loop length you would be comfortable with? What kind of resistance to flow would you expect per hundred feet?
 

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On 1/2 inch, what would be the maximum loop length you would be comfortable with? What kind of resistance to flow would you expect per hundred feet?
that question would depend on a number of factors such as knowing the pump curves etc of the circulator you are using. this can be engineered but is beyoun my capabilities at this moment due to exhaustion and massive alcohol consumption caused by the second blizzard in 5 days
 

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On 1/2 inch, what would be the maximum loop length you would be comfortable with? What kind of resistance to flow would you expect per hundred feet?
As rule i never exceed a 300ft roll usually 250 or so, per loop. Pump size would influence head pressure, GMOD
 

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I have 3 1000 foot loops for the new house, no pump yet, but this will be a passive solar system....may work great, may not. It would seem a lower GPM with sufficient pressure would overcome the length of the loops.
 

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I have 3 1000 foot loops for the new house, no pump yet, but this will be a passive solar system....may work great, may not. It would seem a lower GPM with sufficient pressure would overcome the length of the loops.
J, i am no expert, but 1000ft sounds to long regardless of the GPM, the real problem i think will be heat delivery, by the end of 1000ft you will disapate all your hot water, GMOD
 

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This will be a lot of experimenting for me....I decided to add the loops as an afterthought, and the guy who drills our water wells said my layout will not work. Now, that said, I can calculate the volume, the time it takes to make a loop, and then test the temp losses. It will be fun, and I bet I make it work. If it was my primary heat source in the new home, I would take it more seriously, but like I said, an afterthought. We will be building an inground pool, so I planned on having solar water panels for the pool...if this works, I will get year round use.
 

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I have done a lot of these in the UK and the company you buy the pipe from send out a rep to measure the rooms. They will then normally give you a layout on a sheet of exactly how you should lay the pipe. depending on length you may have to have multiple zones per room. It's not as simple as just placing them a set distance apart. They take into consideration sub floor type, size of room, construction of building, how many windows per room, R values of walls, how many external and internal walls per room, heights of ceiling and so on. It's basically the same as sizing for rads but a bit more technical.



 

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My ex plumber quit the biz and now works in a supply house doing their radiant design/sales. The heat loss calc is a very big key but he told me that generally he prefers to keep spacing at 6", keep runs under 300' or depending on room layout keep areas so they can be sub-zoned. He accomplishes this with individual valves on each loop that he runs so he can throttle back a particular loop within that zone. Also mixing valves on each full zone so if he wants hotter water going to one area that maybe has more heat loss than another, outside temperature anticipators, variable flow pumps, etc.
Joasis, 1000' is way too much. To give you an idea, I have 1500sqft in radiant slab. My design was done by the now defunct "Heatway". I have 9 loops and the longest is 175' (all 3/8 tube). Back then they did the design with 6" for this area, 9" that area, 12" other area and it is the worst set up.
I wish I had done 6" everywhere like my ex plumber suggests. I completely ripped out all my piping (between boiler and point where tubing enters the slab) and redid it because Heatway's engineers must have been smokin something when they came up with that design. It never worked. My first two winters I was constantly on the phone with them. Somewhere I have filed away all the technical info I had to find. The one key is BTUper linft. of tubing based on sizes of tubing. The most valuable resource was hydronic heating books from a guy named Hallahan (sp?).
My new plumber came over and we both did the piping when I ripped all the old Heatway out and he thought I was crazy all the stuff I was telling him how to do based on the book. When we finished I gave him the book. He took it read it and then piped his pole barn with radiant based on the methods in it and he loves working out in his shop now.
 

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No plumber will tell you this, but in concrete you can space 18" on the inside runs. A couple of outside loops at 8-12" and your good. The concrete will evenly heat over time, about a week for my 1600 sq. ft. basement. Once it is up to temp, the pump for the basement runs about 1/3 the time of the upstairs. Think of the slab as a big radiator, we go downstairs to warm up from outside.

I agree with the 300 ft. length. Temp drop is too much on a longer loop. Seperate zones for every room in the house is pretty much a joke as far as I am concerned. I honestly think if I had one zone upstairs and one downstairs, I would be fine. I put in 5 zones upstairs and 3 downstairs and played with the valves, but never really made any difference. I did however maintain a 325 foot max loop, thats why I ended up with 5 loops. Also upstairs the spacing is more like 9".

I will agree with Joasis, you will make your longer runs work, but probably a little steeper learning curve. I have said it before, radiant works great establishing a base heat source for the house. You need some sort of suppliment to react to big temp swings during spring and fall because radiant is a little slow to react.

A warm floor makes for happy feet.
 
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