Keep pex out of concete?

[gogolf0401]

So my neighbor stopped over tonight and we got talking about my radiant heat in my shop that I'm building. I said I planned to put down 2" XPS and staple the pex to the foam and then rebar on chairs (spaced 24") and 5" of concrete over all of that. So the pex will be in the concrete somewhat. He gave me a scared lookand said I don't think that's a good idea. He said if the concrete cracks and shifts it can break the pex tubing since it is in the concrete. He said that he was told to put the pex in 4" of sand and then concrete over that.

I think he has a point and I wish I would have thought of this sooner, but everyone else that I have talked to, including my own extensive research, never said to keep the pex out of the concrete.

Anyone ever have trouble with having the pex in the concrete? Someone up north like me?

 

[pwl]

Never had an issue. Its been in my house for about 12 years. Just put it in my new 40 by 60 garage.

 

[Smokenarrow]

nonsence, if your floor cracks and shifts enough to break that tubing, you will have much much more to worry about than the pex in your floor. Do it the way you described. My 50x40 is fine after 5yrs of buried pex in the floor.

 

[slip knot]

yeah, if the slab shifts enough to break the pex. that will be the least of your problems.

 

[jeepinerdeep]

I'm not a heating expert but I would think putting your pex 9 inches below the surface would just be trying to warm the earth and not the shop. Me think he bumped his head.

 

[CNGsaves]

OP . . . . . was this the propane salesman trying to convince you to heat Earth ??

+1 to put pex in concrete as you had planned. All the Canucks across much colder Canada have their pex right in the concrete and they're much colder than Minnesooooooota !!

Now it California turns arctic with 40 below temps, and you want radiant floor in garage on top of San Andreas fault . . . . Then . . . ONLY then . . . should you go with that lunar idea to put pex down in the earth.

 

[gogolf0401]

Well I meant that the sand would go on top of the 2" XPS after the pex was laid.

 

[shelbyz28]

That seems to come from an older school of thought. All if my current research agrees with the previous posters, pex in reinforced concrete is fine. The one deviation is at an expansion joint (not a control joint) where there is still recommendation to sleeve the pex to help protect it from movement between slabs, but that's for BIG stuff or between structures. I have control joints cut in my floor, pex in concrete, no sleevs. Had I done a heated pad outside my shop (ice melt) I would've at least sleeved it between the building and pad.

 

[gogolf0401]

OK, good. Pex in the concrete it is. Thanks for the confirmation guys!

 

[beakie]

nothing wrong with his idea too.

2+" of foam board
4-12" of sand w/pex in it (thicker the better, but I'm sure there's a point of diminishing returns)
concrete with rebar in it

this is a form of stored energy.
sand is a cheaper method of storing the heat than equal thickness of concrete.

heat still radiates up, concrete still gets warm, but now there is X" of mass heated to the temps you want.

say you used electricity to heat your water for radiant heat. crank the heat @ off peak times, then lower them @ peak times. the slab/sand stays warm for a long time, but you're not paying top $$ for it.

 

[James-W]

nothing wrong with his idea too.

2+" of foam board
4-12" of sand w/pex in it (thicker the better, but I'm sure there's a point of diminishing returns)
concrete with rebar in it

this is a form of stored energy.
sand is a cheaper method of storing the heat than equal thickness of concrete.

heat still radiates up, concrete still gets warm, but now there is X" of mass heated to the temps you want.

say you used electricity to heat your water for radiant heat. crank the heat @ off peak times, then lower them @ peak times. the slab/sand stays warm for a long time, but you're not paying top $$ for it.

That is an interesting way of looking at it.

 

[shelbyz28]

I agree it would still work. The down side is the response time increases, due to the additional mass.

 

[Kidder02]

Used to work for a farmer who did this method. Foam board, pex, 4" sand, then concrete. His explanation was that if he ever wanted to drill into the concrete to mount anything, he wouldn't Nick the pex. Shop heated fine.

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[beakie]

I agree it would still work. The down side is the response time increases, due to the additional mass.

if I was keeping my shop heated round the clock, I wouldn't consider this a concern.
but I wouldn't consider using radiant flooring heat unless it was round the clock, as "response time" would be loooong regardless. compared to forced air/radiant tube/woodstove/etc

Used to work for a farmer who did this method. Foam board, pex, 4" sand, then concrete. His explanation was that if he ever wanted to drill into the concrete to mount anything, he wouldn't Nick the pex. Shop heated fine.

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I never thought of that, and it's a valid point, bonus!

 

[94legaleagle]

Do you need to put poly down, like 6 mil plastic, before you put the extruded poly styrene down?

 

[gogolf0401]

Do you need to put poly down, like 6 mil plastic, before you put the extruded poly styrene down?

Yes

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[BadgerBoilerMN]

Sand is for sand boxes.

The PEX goes in the slab for cost of installation, performance and system efficiency.

I wouldn't take any advice from your neighbor.

 

[gogolf0401]

Sand is for sand boxes.

The PEX goes in the slab for cost of installation, performance and system efficiency.

I wouldn't take any advice from your neighbor.

That's what I ended up doing. But I still think it is a valid point to have sand for extra heat storage.

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[BadgerBoilerMN]

If you have a need or storage there are engineering standards.

The only valid need for storage is to accommodate intermittent heat sources such as wood, solar or off-peak electric. Even so, a water storage tank is preferred where comfort and efficiency is the main goal.

 

[gogolf0401]

Makes sense

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