# radiant tubes in a concrete slab-dumb question



## captaintone (Feb 21, 2009)

I am looking into radiant heat in a basement slab and thought about the concrete cracking.  Does the cracking affect the tubes?  Meaning would I have to worry when the concrete cracks.  Is it going to destroy the tubes?


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## mtnmizer (Feb 21, 2009)

Not a dumb question at all.


   Small cracks haven't seemed to bother my system.  I
would imagine if major cracks were to form, ie shifts in
levelness or large ones would.  The older systems with
copper pipe were known to be problematic from cracks.

  We really like our system.little .cracks will cause problems to 
tile if not put down correctly


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## captaintone (Feb 21, 2009)

mtnmizer said:
			
		

> Not a dumb question at all.
> 
> 
> Small cracks haven't seemed to bother my system.  I
> ...



Well thats good news.  Is there any room for expansion when the tubes are installed?  I mean are they layed tight or do they allow for some movement?  Did you do anything different when pouring the floor.  Like extra re-bar, thicker slab...


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## deerefanatic (Feb 21, 2009)

What was done on our shop by the previous owner was he laid a 6" sand bed down, put the pex in that, then poured the concrete over the top...... but, it takes a LOT of heat to get that system up to temperature initially.......


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## sweetheat (Feb 21, 2009)

My slab-on-grade is somewhat overbuilt because of the point loading going on there from a post located every 14 feet. We used 2X12 form boards around the perimeter. The honch or outer 2 feet is thicker and has more rebar. #4 bars 12" OC. The inner slab comes up to approx. 7" thick with #4 rebar 2' OC. Blue styrofoam 2" thick is under all surfaces. I now wished I'd placed 2" styrofoam around the outside of the edges of concrete as I see lost BTU's melting the snow about 6 inches out. The floor has small drying cracks visible close to the bundled pex close to the manifold. Nothing structural, just a small thin surface crack. I've kept my eye on it and it seems to be OK to date. Concrete pour was in done in 1991, 2009 it's still the same. We used 3400 PSI concrete.  sweetheat


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## DaveBP (Feb 21, 2009)

Any place  PEX tubing runs across an expansion joint in a slab, the tubing should be run through a sleeve of black poly pipe a foot or two long to prevent pinching the tubing. It should be taped to the tubing to keep concrete from getting between the tubing and the sleeve. Not a dumb question. It can be a real problem.

Welded wire reinforcement is the standard way to protect slabs from moving when they crack. It doesn't keep them from cracking, but it keeps it from becoming more than a visible crack. Good place to tie the PEX down, too. 

To minimize cracking, the mix plant can throw in various "admixture" chemicals that reduce the amount of water that has to be added to make the concrete easy to work with. More water added to the mix, more contraction in the slab as it cures. Most crews just keep adding water as they work to keep the mix fluid and easy to screed off. Check with your contractor for the price of whatever your local plant offers. There are a number of different ones available.

Fiber can also be added. Short polyester fibers that are added to the mix at the plant. The fiber can be almost as good as welded wire. Or no good at all according to some. Our local septic tank manufacturer switched to fiber, replacing wire. It leaves little hairs in the surface of the finished slab that some people hate the look of, though.

Whatever you do, insulate beneath and around the outside edge with rigid foam. If your contractor is unwilling to use anything but bubblewrap, look for another contractor. Put heavy poly film under the insulation. A basement floor doesn't have to be damp in the summer and it should be easy to heat in the winter.

Some of my opinions, anyway.


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## mtnmizer (Feb 21, 2009)

A picture being worth a thousand words, here's how mine was done
before the pour..The mixture was a standard 6 bag with fiber.  The
expansion cuts were made a few days later.  So far so good.  The
guys who did this have many under their belts..


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## djblech (Feb 21, 2009)

I agree with what is being said. Poly under 2" of ridgid foam. Wire or steel reinforcement is not needed in a basement slab because it is at a constant temp. You can put fibers in but not necessary. Minimum of 8" of compacted sand under foam, 12" or more is better. Make sure you have drain tile outside if loose soil, outside and inside to a sump if heavy soil. I am a contractor and have learned some of this the hard way. Unfortunately on my own house.

djblech
Greenwood 100
Stihl 170 and 360
Kioti dk45 and dump trailer
120 acres of woods


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## oldmilwaukee (Feb 21, 2009)

ditto on putting pipe insulation around the pex extending 1 foot into the slab on either side of any expansion joints.  that's what I did.  our slab (2200 square feet) was poured in 3 different sections.  I don't trust the fiber stuff - I've seen it crack, and once it cracks, what's keeping the slab from moving further? go with steel.  I used 3/8" rebar instead of the mesh, but mesh would probably work fine.

My parent's house has copper radiant heat in the slab - 50 years old and still working.  1/8" cracks in the slab have messed up the original tile, but not the radiant heat.  I presume it still works today because of rebar in the slab.  I wish my grandfather were still alive so I could ask him how he did the slab.


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## djblech (Feb 21, 2009)

One other thing, my masonary contractors are saying that the water temp should not exceed 140* and 120* is better. If you have metal reinforcement and the temp is to hot the metal could expand faster than the concrete causing cracks. Makes sense if you think about it. Could also be problems with hot and cold zones expanding differently.

djblech 
Greenwood 100 
Stihl 170 and 360 
Kioti dk45 and dump trailer 
120 acres of woods


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## captaintone (Feb 21, 2009)

Hey thanks for the info.  There is a lot ot consider.  I am in the planning stages of building and want to get things right the first time.  I plan on using a garn system to heat the home.  I have heard you can heat the slab at very low temps.  100 or less.  is this true?  one more question I plan on having a garage not attached to the home.  It will also have a concrete floor and I have thought about also using radiant in there.  any suggestions on the garage floor, or is it the same as the basement slab?


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## 2.beans (Feb 21, 2009)

theres a new rubber mat ive seen installed that has a higher r value then the blue board. blue board doesnt lay flat on the ground unless you spend lots of time with a rake causing air pockets which contributes to cracking. definitely do not use bubble wrap. you can heat the floor with real low temps but i wouldnt worry about cracking it with to hot of water. i send 140* plus water to my outside walk ways that are well below freezing with no cracks. once you get the mass hot it holds the heat for a long time. make sure you have a real good plumber/engineer figure out your heat loss and tubing arrangement before you start because once its in there no going back. i have a 1600sqft build with radiant floor that currently cant keep up, that sucks. hopefully ill have it working for next winter.


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## tom in maine (Feb 21, 2009)

Be advised whenever you are looking at any insulation, it is the R value per inch that is important and "mats" are going to have a lower insulation value than rigid foam insulation. I think people get freaked out over Styrofoam cracking when they have to walk over it. This is not a big deal. If you are concerned about slab cracking, use fiber reinforcement and proper grading/compaction.

Most mat-like materials are going to be R-1-3 per inch of thickness. In northern climates, R-10 is typically used for insulating slabs and I think R-15 is advisable. 
The other issue is the true compressive strength of any of these materials.

Most bona fide insulation materials are certified by Factory Mutual, which is an accredited industry standard for rating insulation value.
I have seen a lot of floppy mat manufacturers who use someone who skews numbers and makes a lot of bogus claims about their insulation value.

Be wary of "new" insulation products. If they sound too good to be true, there is usually a reason for that.


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## djblech (Feb 21, 2009)

Slab on grade like in a garage or slab house has different issues like frost protection. A typical basement is in the ground 5' to 7' or 8'. This and the constant temp eliminate frost problems. A slab on grade should have the foam down 18" to 24" and out 3' to 4' around the perimeter as well as underneath to keep the frost from going under the slab and lifting it. This also prevents heat from leaching into the ground.

djblech 
Greenwood 100 
Stihl 170 and 360 
Kioti dk45 and dump trailer 
120 acres of woods


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## in hot water (Feb 21, 2009)

the slab is only as good as the subgrade below it.  That is the biggest problem I see when slabs crack and move.  Uniform thickness in the pour helps also.  A good base of level and compacted base rock on a stable excavation is the best way to start out.

2" of foam under and around.  Have a metal flashing company bend some Z flashing to cover and protect the edge of that perimiter insulation that may be exposed.  Crete-Heat is a great foam product with knobs to snap the tube into, and a vapor barrier covering.  Pricey but a real labor saver, no need for unwieldly wire mesh 

Small shrinkage cracks are common in large slabs.  Don't water down the mix when it arrives will help eliminate small cracks.

Most large slabs get control joints sawed into them after the pour, then fill the cuts with butyl caulk.  Sawed joints are much nicer looking than a troweled control joint.  Unless it is a very large slab I doubt you will have expansion joints.  I've installed up to 16,000 square foot slabs without expansion joints.  But they were cut on a 12 foot grid right after pouring.

Fiber added to the mix can help stop small cracks from traveling across the slab.  It is tougher to finsh with all that "dog hair" in it.  A power trowel at the end will burn off the fibers for a smooth finish.

Not too smooth for a shop slab or it gets slippery when wet.

It's nice to sleeve the pex where it comes through the slab to the manifold.  I use scrap 1" PAP tube to bend some protectors.

Take pictures and document the layout if you need to anchor into it later.

 hr


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## heaterman (Feb 21, 2009)

captaintone said:
			
		

> Hey thanks for the info.  There is a lot ot consider.  I am in the planning stages of building and want to get things right the first time.  I plan on using a garn system to heat the home.  I have heard you can heat the slab at very low temps.  100 or less.  is this true?  one more question I plan on having a garage not attached to the home.  It will also have a concrete floor and I have thought about also using radiant in there.  any suggestions on the garage floor, or is it the same as the basement slab?



Depending on the heat loss of the building the water temp can be very low. I have a couple structures running 95* water at design temps here. (-8*) Lower yet at "normal" winter temps.
Designing and installing a system that can use very low water temps has a huge number of advantages in the long run regardless of the source of heat input..................It is snowing so hard here right now I can't see the big church only a block away from my house.


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## Der Fuirmeister (Feb 21, 2009)

If installed correctly pex radiant floor tubing is a terrific way to heat.  And the hairline cracks that will appear should not be a problem.  Our 10,000 sq ft shop has pex throughout. We used 2 inch rigid insulation around the perimeter of the slab inside, and along the wall down 4 feet on the outside. A closed cell poly foam is recommended under the balance of the slab interior (away from the walls). The largest heat loss is the perimeter where the temps drop along with the outside air. Once you get more than 8 feet in from the wall sub-slab soil temps run what they do 8 feet under the surface outside, or around 50 degrees around here. The sub-slab heat loss is far less than at the wall. The idea is to maintain 80 degree floor temps in our shop.

Not all "rigid foam" is the same. There are three types commonly used in construction. It comes with different compressive strengths and water absorbing properties. I would not use 15 psi foam under a floor. 15 psi foam would be better inside a wall. If you are going to use rigid foam, I'd recommend the 25 psi foam. Better yet, use a closed cell foam designed for use under concrete. See links attached.

Some fibers work. However, not all fibers are the same material. Some are plastic and some fiberglass. Not all steel mesh is the same. It comes in different wire gauge and spacing. We used both fibers and #6 mesh 6" X 6" (what's referred to as highway mesh) in the bottom inch of the pour.  We put the tubing on top of that and tied it with "zip ties".  Then we added another layer of 6X6 mesh on top of that. Then we used 5000 psi concrete and cut it on 10 foot centers. The engineers told us 100 sq ft is recommended for cuts. No more than 150 sq ft (ie 12x12=144).  We poured in sections and used the recommended two foot pipe sleeve centered over the joint.  We also sleeved the PEX inside long radius pvc pipe where it comes up out of the slab (electrical conduit radius, not plumbing radius).  We also added re-bar dowels at the joints. Under the slab we compacted 2 feet of 1-1/4" "traffic bond" (which is limestone with fines), in 6 inch lifts, compacted to 95%. It was like concrete before we poured. 185 yards of concrete all brought in by wheelbarrow to protect the tubing. We've run many 50,000 lb loads over the 6" thick floor. No surface cracks. Any cracking has been controlled with the relief cuts.

The PEX spacing is used to determine the heat output. 120 degree water temp is recommended max. It does not work to space the tubing wider and run hotter temps. Space tubing closer on the perimeter where the heat loss is greatest. Wider in the center of the room. There's more not much on this web site for in slab radiant heat info., and not to hijack the post, but you can find lots of information through some of the links below. 

I'm looking forward to connecting a gas'er to the shop in-slab radiant heat system some day.


http://www.backwoodshome.com/articles/hackleman64.html
http://www.pexheat.com/
http://www.radiantcompany.com/faq/#cost
http://www.thebarrier.com/
http://www.slabshield.com/index.php
http://www.radiantsite.com/
http://www.pexsupply.com/categories.asp?cID=355&brandid;=


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## yooper rich (Feb 22, 2009)

Great question captaintone.  I hope to be doing the same thing on our new home construction project this year and like you said, we want to get it right the first time.  Thank again for all the info from you experts.


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## AOTO (Feb 23, 2009)

I have a 32' x 48' barn that has Radiant heating.  I used 2" blue board with Tekfoil bubble on top of that. I also used Pex-Al-Pex 1/2" tubing. So far this year it's worked out very well.  It is nice and cozy in there at 52-54 degrees. I should note that I have a few stress cracks near the corner of the doors and I used 2400 PSI (I think) Cement with no rebar.


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## GKG-MO (Feb 23, 2009)

I have poured literally hundreds of pex floors and the cracks will not effect the floor at all. A common misconception is that a concrete floor expands. Concrete just like everything else shrinks when it dries. Cracks most often form from the concrete being stressed because of a inside corner or different consistences in the mix. 
      The most important thing in a pex pour is *be careful*. Lay plywood over the pex to run wheelbarrows on so not to cut the tubing. Be extra careful when you dump the wheelbarrows as the cleat in the front can cut the tubing with 150lbs of concrete in it. Make sure the tubing is pressurized to around 100 psi so if you do cut it there is an audible sound. Also a pressure gauge is a good idea. Check it throughout the pour. If you cut a tube and it has to be fixed after the floor is dried it can be pricey. Much easier to fix it and then go on.


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## barnartist (Feb 23, 2009)

GKG is right. Do all of what he said. Spend the money on the insulation. Just do it. I also learned the hard way.

A side note here. Any of you watch the planet green channel? I watched a show the other day, they were rebuilding a John Deere dealer in Greensboro- the town that was hit by the big tornado.

Any way, I CANT BELEIVE i saw them-and filmed this, but they were installing the radiant heat, and actually showed the contractors only using the bubble wrap for insulation. This was one huge building. They are using corn for the heat sourse. I can't imagine how much more corn they will need to heat it now...


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## yooper rich (Feb 23, 2009)

mhvfd,  how is the Pex attached to the blueboard?


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## Deering (Feb 23, 2009)

Here in the SE Alaska rainforest we have lots of wood, but getting it to dry can be a challenge.  I'm looking at installing a boiler in an attached shed (yet to be built) along with wood storage.  I'm starting to think that insulating the shed, installing a HRV, and heating it off of the boiler it is the way to go.  

Pex in the slab where the wood will be stored seems like one promising option, but I may not want to keep the shed heated once the wood is dry.  Can pex in the slab with water in it be allowed to freeze?  Will the tubing fail or the concrete crack?  Or do I have to blow it out or go with glycol?


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## heaterman (Feb 23, 2009)

barnartist said:
			
		

> GKG is right. Do all of what he said. Spend the money on the insulation. Just do it. I also learned the hard way.
> 
> A side note here. Any of you watch the planet green channel? I watched a show the other day, they were rebuilding a John Deere dealer in Greensboro- the town that was hit by the big tornado.
> 
> Any way, I CANT BELEIVE i saw them-and filmed this, but they were installing the radiant heat, and actually showed the contractors only using the bubble wrap for insulation. This was one huge building. They are using corn for the heat sourse. I can't imagine how much more corn they will need to heat it now...



There's a LOT of ignorance out there, even amongst supposed professionals and it makes me madder than a wet hen. They don't seem to understand the basic premise of radiant heat is that it travels in ALL directions from the source. The myth commonly quoted is "heat rises" This is not so. Hot air rises but radiant energy travels 360* from the source until it strikes an object that it can dissipate its energy on. Think about the heat from the sun, traveling 93,000,000 miles through space at a temp near absolute zero. How the blazes does it make you feel warm when it gets here? Duh! It's not hot air, it's radiant energy. Once you understand that, common sense dictates that you need something to block the heat flow into the earth and direct it toward the area you want to heat. Radiant heat done poorly will suck mind boggling amounts of input.....as the guys in that JD dealership will soon find out. Green my butt.  

I gave a quote to a local business that was putting up a 10,000 sq ft machinery repair shop. I was too high mainly because I quoted 1-1/2" blue board for the entire floor while my "competition" insisted that double bubble was all they needed. The customers urge to "save money" led them to select the other contractors proposal. They burned up a large HeatSource, a 6048 CB and now have a huge OWB that they load wood into with a forklift on pallets. I don't know the brand. They can't get the building above 50* when the OD air temp hits 0, they burn over 120 pulp cords of wood per season and they can grow tulips around the building in February.  Now they are considering abandonment of the infloor and installing overhead fan forced heaters. In their case it's probably the best option they have. Truly sad!


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## BrownianHeatingTech (Feb 23, 2009)

Deering said:
			
		

> Pex in the slab where the wood will be stored seems like one promising option, but I may not want to keep the shed heated once the wood is dry.  Can pex in the slab with water in it be allowed to freeze?  Will the tubing fail or the concrete crack?  Or do I have to blow it out or go with glycol?



You will need to blow it out, or use glycol.  To avoid filling the whole system with glycol, you can separate that zone with a heat exchanger, if necessary.

Joe


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## barnartist (Feb 23, 2009)

Heaterman, a few years ago, my cousin did the same thing. Used some kind of black roll material, it had 2 layers of bubble and maybe a thin layer of foam. My cousin can't keep enough wood. He abandoned a gasifier for a CB. Now we are looking for other options. I love my radiant heat in my house. I still feel bad for those who messed up, because now it can't be fixed.

It would be fun to talk to the John Deere owner in a year or 2, see how they are doing.


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## sdrobertson (Feb 23, 2009)

barnartist said:
			
		

> Heaterman, a few years ago, my cousin did the same thing. Used some kind of black roll material, it had 2 layers of bubble and maybe a thin layer of foam. My cousin can't keep enough wood. He abandoned a gasifier for a CB. Now we are looking for other options. I love my radiant heat in my house. I still feel bad for those who messed up, because now it can't be fixed.



Probably cheapest way to fix this problem would be to find a junk furnace and hook it up to a water to air heat exchanger.  He could even run a little duct work to heat the whole building.  Not ideal, but cheap and he could use filters to clean the air also.  I vote for a new federal "radiant heating czar" with allot of important regulations of maybe some education for installers.


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## BrownianHeatingTech (Feb 24, 2009)

sdrobertson said:
			
		

> I vote for a new federal "radiant heating czar" with allot of important regulations of maybe some education for installers.



Could we just have subsidized clue-by-fours, instead? 

Joe


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## AOTO (Feb 24, 2009)

yooper rich said:
			
		

> mhvfd,  how is the Pex attached to the blueboard?



It is attached via these little black clips that look like the opposite of a fish hook.  It was done by this stapler looking thing that had the black staples push down on the tubing and as it goes into the blue board, it hooks on the out side of the clip.  I'll get my camera and take a picture of it.  I saved a piece of the insulation set-up that shows everything. My barn also has no problem staying above 50, even when it's 9 F outside.


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## GKG-MO (Feb 24, 2009)

mhvfd said:
			
		

> yooper rich said:
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I'm not personally a fan of those plastic U hooks. Once the floor is poured their fine but they tend to pull out during the pour and then the tubing likes to float to the top of your concrete. NOT GOOD. Especially if your saw cutting your expansion joints. Either lay down 6" wire mesh and zip tie the pex to that or they make a clip the screws in similarly to a wall anchor that the pex clips into. They take a little longer to install than the U hooks but easy in, easy out.

As others have said use plenty of insulation. The more you spend now the more you save later. Hot air rises. Radiant heat radiates through the easiest path, witch could be into the ground if your not careful.


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## captaintone (Feb 25, 2009)

mhvfd said:
			
		

> I have a 32' x 48' barn that has Radiant heating.  I used 2" blue board with Tekfoil bubble on top of that. I also used Pex-Al-Pex 1/2" tubing. So far this year it's worked out very well.  It is nice and cozy in there at 52-54 degrees. I should note that I have a few stress cracks near the corner of the doors and I used 2400 PSI (I think) Cement with no rebar.



Great set up.  How long does it take for you shop to warm up?  I only ask because I aslo want to heat  a detached garage.  Its not a place I will be all the time and worry that it will take to long to warm.  Meaning I might be done working in there before the garage warms up.


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## Der Fuirmeister (Feb 25, 2009)

Deering said:
			
		

> Here in the SE Alaska rainforest we have lots of wood, but getting it to dry can be a challenge.  I'm looking at installing a boiler in an attached shed (yet to be built) along with wood storage.  I'm starting to think that insulating the shed, installing a HRV, and heating it off of the boiler it is the way to go.
> 
> Pex in the slab where the wood will be stored seems like one promising option, but I may not want to keep the shed heated once the wood is dry.  Can pex in the slab with water in it be allowed to freeze?  Will the tubing fail or the concrete crack?  Or do I have to blow it out or go with glycol?




Use glycol.  Same for any slab that might freeze.


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## Der Fuirmeister (Feb 25, 2009)

captaintone said:
			
		

> mhvfd said:
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Radiant doesn't react quickly to demand changes like forced air does.  If you need quick / short term temp changes you might consider an added source like a cheap furnace or unit heater to bring up to temp.


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## captaintone (Feb 25, 2009)

Der Fiur Meister said:
			
		

> captaintone said:
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Thats what I thought.  I didnt think radiant would heat up fast enough if I am not using the garage all day every day.  I am going to look into an alternative for the garage.


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## Der Fuirmeister (Feb 25, 2009)

heaterman said:
			
		

> barnartist said:
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Heaterman, What do you recommend to prevent concrete floors from cracking when using foam?

Was the 1-1/2 inch foam what you normally would use?


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## deerefanatic (Feb 25, 2009)

captaintone said:
			
		

> Der Fiur Meister said:
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I and my neighbor were talking on that this last summer. We came to the conclusion that if we EVER pour concrete for ANYTHING that will be inside, we're gonna lay pex in it; just for the simple reason of the pex is a small percentage of the cost of the concrete, and it's not something you can do later.... Even if it doesn't get used for 10 years, it's there if I want it in the future.... Just my $.02


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## Der Fuirmeister (Feb 25, 2009)

Here's a link to a site with more information.  Also some photos of slab on grade etc.


http://www.radiantcompany.com/details/grade.shtml


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## Chris S (Feb 25, 2009)

re:  will cracks affect tubing?

For anyone that has not seen a pex demo....  I was at the Uponor booth at a recent trade show.  They took a piece of 1/2 pex approx 5" long, and put it inti a machine that stretched it to approximately twice it length, without failure.  The center was down to about 1/4" at that point.  They then took a heat gun a it returned back to it's original shape, which not all pex will do but...
The point is that the little bit of stretch you will experience in a shrinkage crack is truly insignificant to the tubing.
A displaced crack,  one that you could trip on is more of a concern.  A small shifting will not break or shear the tubing, but could pinch it if the crack were significant.
As pointed out by many,  a stable base is the best beginning- well compacted etc.


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## heaterman (Feb 25, 2009)

Der Fiur Meister said:
			
		

> heaterman said:
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Best antidote for cracking is a good concrete man, slow set up on the crete and a solid and even grade to pour on. The foam and tube really have little to do with it. 

We use 1.5" foam for 4" pours and 2" for 6" thick floors. Some will say it's a waste but we do the whole floor with the same stuff. 

One thing that you can say is a negative regarding thick slab radiant is response time. You just can't expect that mass of cement to produce heat quickly or to shut down quickly. I have installed what is basically a two stage setup in some places where the owner insisted on turning it down. We usually set up the floor to run at a low temp that will maintain 45-55* and then install some other type of emitter, radiators, baseboard, fan coils to pick up the room temp from the setback point. Best to just minimize the heat loss and let it run. 

Response time for a poorly insulated slab can be measured in days, even weeks, not hours.


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## Greenfield Dave (Mar 1, 2009)

Hi Guys!  Long time lurker, first time poster.  Here's my situation.

I built a 36X48 garage with loft, and used knowledge from this site and others to put PEX in the floor. 1500' to be exact, in 5 zones.  Put 2"pink board down, used the twist in PEX clamps, thought is was Miller time!  But I didn't put clamps at the point of the loops, and they floated up in the concrete mix. Woops!  So we decided not to make saw cuts, it didn't crack too bad, it does have fiber in it.  I have insulated all the 2X6 walls and put OSB on them, but the ceiling will have to wait till money is in season!  I just bought a stainless manifold, and am going to heat the system primarily with my OWB, but will use an electric water heater for backup/supplemental heat.  I have a sidearm heat exchanger, expansion tank, and just enough skills to be dangerous!

My questions for you experts are:
1. How big of a pump do I use?
2. Should I control the incoming temperature to the water heater/sidearm with a tempering valve? Or run that loop wide open and control the temperature to the floor?


 I have a layout of how I think it should be plumbed, but it's too big to attach here.



Wood Doctor 8000
Stihl 041 Farm Boss; 009
POS Swisher log splitter
House heated with an older boiler, old cast iron radiators and under floor PEX

Any input is appreciated
Dave


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## AOTO (Mar 25, 2009)

I'm running with no heat exchanger and I'm using water.  I'm running a Wilo Star 30 to my barn which is 150' from the OWB, then once I get inside, it goes thru a tempering valve and then to a TACO 007.  I am running 6 loops, each at approx. 200-250' each. There is also a little trick about looping the lines no greater than 4 1/2 " before the tempering valve. I can tell you that my barn is warm and zero maintenance, however my wood consumption went up 35-40%, but I blame that on using crappy, cheap, insulated Pex underground.


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## Greenfield Dave (Mar 26, 2009)

Nice Job Burning Chunk!!

I assume the tempering valve was missing from the second picture..  but I understand what you did.  I don't understand the 4 1/2" rule you spoke of either, but always obey it..  I need to use the heat exchanger and antifreeze, as I may have the opportunity to go away in the winter!  HA!  We want to come back to Vermont to celebrate our anniversary this winter, but with the economy, who knows!  

Thanks for the info!!

Dave


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## WRVERMONT (Mar 26, 2009)

Heaterman, sounds like those guys should have taken your quote.  
Below are my tips for a good radiant slab.  
1. Good drained foundation of stone.
2. Insulated with a minumum of 1.5" and better 2" foam board underneath. Insulating the Perimeter is important to.
3. Moisture barrier (polyethylene)
4. The use of wire grid reinforcement will make it strong and also help distribute the heat around.
Below tubing or better yet below and above.


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## RowCropRenegade (Jul 30, 2009)

This thread seamed to be closest related to what I'm doing.

I just excavated out the building.  Put in 6 inches of stone, except for borders.  I bought GreenGuard 2 inch foam insulation for the entire border and floor.  The foundation wall is uneven as hell.  I'm planning on building out a foam barrier  around the jagged areas and filling it with concrete.    I don't want a single area of the foundation exposed.  I'm anchoring the foam board with masonry screws.  Prob 2 per 8 ft. 

After that get the edges filled in with stone, ground perfectly leveled and down with the foam board.  6 mil vapor barrier.  

Comments?


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## heaterman (Jul 30, 2009)

RowCropRenegade said:
			
		

> This thread seamed to be closest related to what I'm doing.
> 
> I just excavated out the building.  Put in 6 inches of stone, except for borders.  I bought GreenGuard 2 inch foam insulation for the entire border and floor.  The foundation wall is uneven as hell.  I'm planning on building out a foam barrier  around the jagged areas and filling it with concrete.    I don't want a single area of the foundation exposed.  I'm anchoring the foam board with masonry screws.  Prob 2 per 8 ft.
> 
> ...



Sounds like you are thinking it through nicely. You basically want to have your concrete slab sitting in a foam tub.


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## RowCropRenegade (Jul 30, 2009)

The vapor barrier above the foam, correct?  Then wire mesh.

They have these stands at lows that hold the wire mesh up 2.5-3".   I thought that made alot of sense for what I'm doing.  6 inch pad will have the pex at exactly 3 inches into the pad.

Comments?


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## Chris S (Jul 30, 2009)

We generally put the plastic down first, though I don't think it really matters.  bar chair, or supports such as you describe don't work especially well with wire- as it's not ridgid. 
What we generally do is lift the wire as the concrete is being placed.  This results in the wire being approximately 1/3 of the way into the slab, which is pretty much ideal.
If the nasons step on it & it's at the bottom, it's not the end of the world.


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## DaveBP (Jul 31, 2009)

> The vapor barrier above the foam, correct?  Then wire mesh.



I put 8mil poly down on the compacted sand and the foam on top of that. I reasoned the foam can take the beating it will get from the crew but the poly film might not be as durable.


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## RowCropRenegade (Jul 31, 2009)

do you also put it under the foam on the foundation?


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## deerefanatic (Jul 31, 2009)

The way our shop was done was a totally different animal...... 

According to the previous owners, they ran the bex in a 6" thick bed of sand below the concrete, so if the concrete ever cracked, it wouldn't break the pipes...

I've never actually been able to heat this shop, but this winter should change that......

I know I have perimeter insulation, but have no idea what's under the sand bed.....


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## Chris S (Jul 31, 2009)

If you saw how much (quality)  pex tubing can be deformed without failing, you would not be concerned about that.


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## heaterman (Aug 1, 2009)

[quote author="deerefanatic" date="1249057996"]The way our shop was done was a totally different animal...... 

According to the previous owners, they ran the bex in a 6" thick bed of sand below the concrete, so if the concrete ever cracked, it wouldn't break the pipes...

I've never actually been able to heat this shop, but this winter should change that......


I've only seen that one time. It was a DIY house and the guy put pex in the basement floor. 1-1/2" foam underneath the basement floor which was l shaped. I went to look at the job to get measurements for him and do a heat loss. The house was built in what amounted to a clay pit and I advised him to take the basement grade down another 6" and fill with sand to get it nice and level and provide some stability under the foam but he didn't want to go to the "extra" expense and time. The basement floor was done in two pours and over the next 3-4 years, the short side of the L settled about an inch. Being that all the tube ran through a door width opening from one part to the other, all the tubes for the short side ran through that. When the slab moved the tube went with it and given the amount of movement, he's had 2 of the 4 loops fail. 

When we go from one pour to another on a slab we always sleeve the tube through the form (PITA) or dive underneath the form board and come back up into the slab. Cold seams are not the best but sometimes can't be avoided.


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