PEX tubing and slab joints

[Chris705]

As I prepare to install PEX tubing in my concrete slab (40'x44' overall size) I have been reading as many manufacturers web sites as I can on the topic. I have also read with great interest the many posts here on GJ about radiant slab heating. I have a couple questions that I cannot find answers to.

I will point out that my intention is to use 3” blueboard insulation under the slab and 1” at slab edge. I plan on using the 6x6 wwm as a tubing layout guide and hold-down with zip ties. I don’t plan on pulling the wwm up or add other reinforcing other than micro-fibers to help w/ shrinkage cracks. I do plan on three saw cuts in each direction on the monolithic pour.

1) In Viega’s site as well as seeing the same thought elsewhere….. I see the installation recommendation about bridging construction (cold) joints and control (saw cut) joints. The Viega site recommends bridging and protecting the PEX tubing of any planned joint (both cold and saw cut joints) with 12” of rigid pvc tubing. So first question is has anyone ever experienced any problems with their tubing installation and use by NOT doing this at joints? I assume for the most part no one does this?

2) My current garage slab design has 7 loops of ½” PEX at 250’ length. I also intend to eventually incorporate future snow melting of a long sloped sidewalk and short concrete drive……I need to install the supply and return lines of these future 4 loops to the edge of the foundation wall and will eventually install the actual in slab PEX at a latter date. The PEX layout for snowmelt again has runs equaling 250’ length at foundation edge and I intend to use ½” PEX. I will run these four loop feeds under my garage slab to where I will eventually tie them into the snow melt and will insulate them for the approx. 50’ they will run under my slab (this makes the tubing runs 300' long). The snowmelt will be on its own zone for manual control. Second question – is there any benefit to insulating the snowmelt PEX as it runs under my garage slab? AND also is there any benefit to using a larger dia. PEX (5/8 or ¾) for this portion (I ask this because I mentioned the long sidewalk will slope…. about 20’ vertical over 125’ run).

Thanks for any and all input!

 

[anthony666]

1) i never bridge the tube at joints .. tube should be at the bottom of the slab and pvc isn't gonna protect against a concrete saw blade .. ive been in the trade for a long time and never had an issue

2) 1/2" pex will not carry enough btus for snow melt applications .. you need at least 5/8ths .. i often just use 3/4" because 5/8ths fittings are a pain to find, most places don't even stock them due to limited application

 

[Highbeam]

I concur. Could you imagine trying to thread on a 12" sleeve hundreds of feet down the loop? I layed out each loop by walking along and unrolling the roll hoolahoop style while my helper zip tied enough to keep things straight. So how would you even put a sleeve on?

If I could do it again, I would staple down the tubes to the pex and lay the WWM on top of the tube to get the WWM up into the mud a little bit.

 

[Highbeam]

Here's a pic of my job, just like your proposal, for fun.

 

[Chris705]

anthony - thanks for your reply, I have read a lot of your offerings on GJ and appreciate your knowledge/expierience.

1) i never bridge the tube at joints .. tube should be at the bottom of the slab and pvc isn't gonna protect against a concrete saw blade .. ive been in the trade for a long time and never had an issue

2) 1/2" pex will not carry enough btus for snow melt applications .. you need at least 5/8ths .. i often just use 3/4" because 5/8ths fittings are a pain to find, most places don't even stock them due to limited application

I figured for the interior slab that there would be little movement and/or expansion and I only planned on providing saw cuts. For the snow melt, long sidewalk, I will need expansion joints, thought I would show what Viega post on their web site. I plan on having inulation under the snow melt area as well and I could route out a channel lay the pex in it and then isolate w/ poly from the concrete at expansion joints (say 12" long), that may work with little added cost or effort. As far as 1/2" vs. 5/8" for the snow melt I have no problem going w/ the larger dia.....to clarify, my initial question was should I use larger tubing from my centrally located manifold to foundation edge, then connect to in slab loops.....but now that I write this it seems I could use 3/4" tubing and easily run the 300' long loops. Does it make sense to inulate the lines that run under my garage slab? And does height come into play when the sidewalk drops 20' below my garage floor slab elevation?

http://[URL=http://s1283.photobucket.com/user/chris705/media/Garage%20Build%202013/construction-controljointdetails_zps5921d2b6.jpg.html] [/URL]

 

[rlitman]

2) 1/2" pex will not carry enough btus for snow melt applications .. you need at least 5/8ths .. i often just use 3/4" because 5/8ths fittings are a pain to find, most places don't even stock them due to limited application

I just bought 100' of 1/2" pex for snow melt based on manufacturer's recommendations, so I'd say that blanket statement is not necessarily true.

1/2" pex is too small to do snow melt on a slab. I'm using it on steps. 1/2" is the only size small enough to safely bend a u-turn underneath a step. So with a 100' loop and two lines under each tread, I think I should be fine. Also, I'm not going up and back on each tread. The middle of the loop is on the last step, then the supply and return side run parallel all the way home.

 

[anthony666]

chris .. if anything the angle of sidewalk is gonna help you .. typically when you tie down pex you end up with a series of very very shallow arches .. each of the high spots between ties is a potential air trap .. the angle of your walkway is gonna help shed that air

you're gonna want to keep the snowmelt system separate from the slab .. the delivery temp requirements are different and the return temperature is vastly lower usually .. and you need to be able to isolate the snow melt completely

honestly, i would seriously think about skipping it altogether .. the cost of running a snow melt system is mind boggling .. i try to talk everyone out of them whenever possible .. they need to idle just above freezing all winter and when they sense snow they spike and guzzle fuel .. typical numbers i use for load calcs are 100 btus/hr per square foot

mr rlitman .. i always use 3/4" on steps .. every 180 is a restriction which equates to more head pressure = bad .. snow melt is all about getting maximum heat out to the area that needs to be defrosted STAT .. there is a way to safely bend 3/4" that tight, you just have to think 3 dimensionally

 

[Modoc]

As I prepare to install PEX tubing in my concrete slab (40'x44' overall size) I have been reading as many manufacturers web sites as I can on the topic. I have also read with great interest the many posts here on GJ about radiant slab heating. I have a couple questions that I cannot find answers to.

I will point out that my intention is to use 3” blueboard insulation under the slab and 1” at slab edge. I plan on using the 6x6 wwm as a tubing layout guide and hold-down with zip ties. I don’t plan on pulling the wwm up or add other reinforcing other than micro-fibers to help w/ shrinkage cracks. I do plan on three saw cuts in each direction on the monolithic pour.

1) In Viega’s site as well as seeing the same thought elsewhere….. I see the installation recommendation about bridging construction (cold) joints and control (saw cut) joints. The Viega site recommends bridging and protecting the PEX tubing of any planned joint (both cold and saw cut joints) with 12” of rigid pvc tubing. So first question is has anyone ever experienced any problems with their tubing installation and use by NOT doing this at joints? I assume for the most part no one does this?

2) My current garage slab design has 7 loops of ½” PEX at 250’ length. I also intend to eventually incorporate future snow melting of a long sloped sidewalk and short concrete drive……I need to install the supply and return lines of these future 4 loops to the edge of the foundation wall and will eventually install the actual in slab PEX at a latter date. The PEX layout for snowmelt again has runs equaling 250’ length at foundation edge and I intend to use ½” PEX. I will run these four loop feeds under my garage slab to where I will eventually tie them into the snow melt and will insulate them for the approx. 50’ they will run under my slab (this makes the tubing runs 300' long). The snowmelt will be on its own zone for manual control. Second question – is there any benefit to insulating the snowmelt PEX as it runs under my garage slab? AND also is there any benefit to using a larger dia. PEX (5/8 or ¾) for this portion (I ask this because I mentioned the long sidewalk will slope…. about 20’ vertical over 125’ run).

Thanks for any and all input!

Chris, great question, I am in the same process as you are in getting ready to build my garage/shop with pex in the floor and that has been one of my main questions also... I have found lots of info on the web, maybe too much in my case... I found a good website when it comes to info about slab on grade slabs with radiant in-bedded and it just say's to cut control joints the web site is concretenetwork.com and there is a lot of info there and as I said before maybe too much.. there is a guy who posts on here about concrete questions who seems very knowledgeable about concrete and has answered lots of questions about concrete, goes by LLwillysfan I believe I would like to talk to him a little more about the same subject.. also I don't believe you will want to use WWM #4 rebar on chairs will be better in MHO but then again that's my opinion and that's how I will do mine and the concrete mix will be another big factor also. Like I said I'm in the process of putting all the spec's together for my build. try googling hydronic heated shop floors and see what you get. I found one forum called I think precision machinist had there where a lot of people that had posted on there about the subject. Hope this helps with your quest. Cheers,

 

[Chris705]

So the concensus seems to be that sleeveing is not needed, Highbeam your insight is good for the practicality of trying to use a length of rigid PVC on a long length of tubing while trying to install. When I get to that point in my sidewalk I will either sink the tubing into the insulation board or wrap plastic wrap around the tubing to allow for concrete slab expansion/contraction at the cold joints and do nothing special in the garage slab.
anthony, I understand the snowmelt maybe a waste of time/effort but if it works well in a manual control to rid the walk of ice I will be happy. I also had planned a separte zone....the complexity of the different zones and temperatures....I hadn't mentioned I plan for a second level floor heat also, my heat loss calcs all totals to about 200K btus....for that reason the snow melt will go totally manual control so I don't waste a whole lot of energy. And the heat plant/zoning/controling will follow later as right now I am concerned w/ getting the garage slab in place by this spring.
Modoc - thanks for your input, I have experience w/ concrete from the specifying side, I understand that a properly installed base is esential for crackfree concrete. The wwm will only be used as a guide to layout and secure the pex.....I am not a beliver in having to reinforce the concrete unless is is a structural slab meant to span weak base material or is supported above grade. That said the tubing and wwm will stay at the very bottom of my pour. I will see what more I can learn from your link.

Thanks for everyone's input!

 

[custom1]

The concrete guy for my slab used "Zip-strips" where you would normally cut control joints. They are "T" shaped and go in while the concrete is wet and then they pull the top part off and it leaves a plastic strip in the concrete. No cracks anywhere in my slab yet. It was poured in 09 I think. That way there is no worry about hitting any pex later with a saw. I did not use any reinforcing at the joints, only the 90 degree elbows where the lines come out if the floor.

 

[Jackfre]

I had snow melt in my sidewalk in MA. It was a manual system and while I only used it occasionally when we got a big storm and I got ahead of it, it was really nice looking out at a dry sidewalk with straight 24" banks of snow on either side. I had a lot of elevation change on that sidewalk so it was good. Was it worth it? Hmmmmm-no, in hindsight, but I did it all myself so it was okay. Pricey on material, time and operation...but did I tell you how cool it was to look out the window on a snaky morning...

 

[Chris705]

anthony - wondering if you could comment on the question I had about how to get from where my manifolds will be to the edge of the foundation wall for the future snow melt....should I run these four loop feed/returns under my slab insulation (I would insulate these lies w/ armaflex) or doesn't it matter if they are installed above the slab insulation, uninsulated? Thanks!

Custom1 - are the zip stips installed as straight as a saw cut would be in your pour? If I follow the website correctly you use a jointing tool, lay the strip in and then just trowel over the whole thing.....is that how you saw them being installed?

 

[anthony666]

sorry chris .. my bad

i always try to rough in feeds under the slab

make a trench, line it with vapor barrier, armaflex your pex, fill the trench with spray foam, flip the vapor barrier over the top and back fill

the armaflex keeps the hot and cold feeds apart .. the vapor barrier keeps everything dry .. the spray foam insulates

the biggest reason for running your lines under the slab is the return temp from a snowmelt is always very low and the amount of condensation it causes will blow your mind .. i run them undernaeth the slab insulation .. i want snowmelt away from my indoor heating system, like i mentioned before, the return temp is often unbelievably cold

when you spec your boiler, make 100% sure it can handle low return temps .. i'd go so far as to email the manufacturer and be sure it's gonna be ok .. it's not good for a boiler to be thermally shocked

 

[Chris705]

Anthony - great I can do that. Most likely when I get to the boiler and controlling I will reach out to you thru another posting. Hopefully around this time next year!

 

[anthony666]

sure thing chris

 

[custom1]

Chris, I don't recall exactly how they did it that day. I don't remember them using a tool first. As far as the straightness goes, there is not really a groove in the floor to draw your eye to. It is just a line where the plastic is and I don't pay much attention to it. My garage used a good bit and is not the neatest place. I don't have epoxy or anything, just the curing sealer they put down after power finishing the floor. Its nice and smooth and easy to sweep, but not a show place.