How to install radiant tubing on the thickened edge of monolithic slab?

superwoman

HI,

I'm doing a 6" monolithic pad with thickened edge 18" edge sized 30'x12'


I have two questions:
1. How do I install tubing on the thickened section? I assume I have to lift it somehow?
2. Is it worth to lift the tubing up from the 6" slab to the middle of the slab? I initially planned to use panel like Amvic but that entails tubing at the bottom of the 6" slab.

Zman

I would put the tubing about 1/3 from the top of the slab tied to rebar on chairs. At the outside, keep it the same ~2" down.
Your outside edge insulation leaves a lot to be desired. The insulation would be better if it came to the top of the slab with metal flashing to protect it.

superwoman

Zman said:

I would put the tubing about 1/3 from the top of the slab tied to rebar on chairs. At the outside, keep it the same ~2" down.
Your outside edge insulation leaves a lot to be desired. The insulation would be better if it came to the top of the slab with metal flashing to protect it.

Thanks.

If I decide not to use WWM wire mesh and use fiber reinforced concrete, what other method can I suspend the tube 2" from the top? Will chair still work? I heard concrete crew will just stomp and knock over chairs when they pour...

Thanks the tips about edge insulation, I will modify to your suggestion.

hot_rod

get it up into the slab, 2” below the top ideally. Downward loss will be considerable with that thick uninsulated mass. Really not a good way to detail that type of pour😙

Zman

Most crews will not consistently pull up the mesh. If you specify rebar tied to concrete chairs, they really have no choice.

Derheatmeister

We did a monolithic Slab in Camp Hale , Colorado
A couple things to consider:
1.The Outside parameter of the Slab needs to be insulated all the way upjust as Zman recommeds. BTW some areas such as Boulder County are now requiring 4" vs the 2" of Polystyrene as an edge insulation..
2. Chairs work but 250 LBS Concreate Contractors do not like working on a Trampoline and the plastic chairs just buckle under the weight of multiple contractors exspecially when the sun warms the plastic chairs up.. Also when the contractors step on the wire between the chairs it bends the wire and the tubing can start to surface...Best would be to use Rebar in conjunction the wire mesh and save the money on the Helix/fiber.
With the mesh only we use Concrete Chairs approx.1 foot apart that have a wire to HELP avoid this problem. Still....While the slab is being poured you may have to advise the crew that the tubing is to be respected.. Bring Donuts and Coffee
3. Talk to the Concreate Contractor well in advance prior to the pour to make sure that he and his crew are understand that the placement of the tubing is to be respected and sharp objects such as the edge of a wheelbarrel are to be kept away from the tubing..
4. Tubing should be approx. 2" from the surface to avoid lag time... 6" is way to deep !
5. Install a Pressure switch/gauge with watts Loud mouth.. and have some repair couplings on site while the slab is being installed..

hot_rod

your best bet is to let the concrete crew know of the challenge. Make sure you have a radiant friendly crew
if they stomp chairs, you have the wrong concrete contractor😂

superwoman

Thanks all.

What about using 2" high concrete paver as "chair" like this https://www.homedepot.ca/product/oldcastle-cobble-lite-paver-charcoal/1000402080

It might be more sturdy than any chair and crew will have no choice but to work with the elevated mesh.

PC7060

I’d be concerned you’d be leaving weak spots in concrete. With a 6” slab you would have to turn on edge to get mesh where to want it so would still be tippy. 

PC7060

I recently saw a discussion with picture where the installers used electrical pvc conduit to as chairs and to hold the tubing in place. Nice options since very tough and won’t crush. 

That was probably only a 4” slab though. 

Found it in this thread, posted by @boiler_jim. 

https://forum.heatinghelp.com/discussion/comment/1655736#Comment_1655736

MLJ

Let's get real here....keeping the tubing in the middle of the slab is textbook and a dream....have use the 2" foam that you snap the tubing into on 6" pours have had no problems heating...I think your best to use rebar, not the mesh....mesh can expand and contract more so than rebar

MLJ

One more thing make sure no one is smoking on the job.....had a job one of the concrete guys toss his cigarette butt out into the pex field (3300 sq ft)....burnt a hole into the tubing. We were watching the pressure gauge while they were pouring and noticed a drop in pressure and were able to find and repair the hole while they were pouring the concrete.

Zman

MLJ said:

Let's get real here....keeping the tubing in the middle of the slab is textbook and a dream....have use the 2" foam that you snap the tubing into on 6" pours have had no problems heating...I think your best to use rebar, not the mesh....mesh can expand and contract more so than rebar

If you use rebar on concrete chairs, you can get the tubing wherever you like. It is arguable whether only worth the extra effort. I insist it is done this way on large commercial snowmelt jobs and recommend it for other installations.
You can usually heat a slab from the bottom. It requires higher water temps, increases downward heat loss, and fly-wheel effect.
How does mesh have a higher expansion rate than rebar? I would think it is the same steel in a different form.

hot_rod

Take a 4" concrete slab, tube at the bottom will increase the downward loss about 10%. All things being equal, tube at the bottom 17 BTU/ sq ft, 2" below get you 23 BTU/ft output. Somewhere around a 8°increase in SWT to get outputs equal. Plus slower ramp up time. So you have to decide if the time and effort is worth the tradeout.

Those looking to use A2WHPs would be well advised to get the SWT as low as humanly possible to get the COP you are paying for. You get one chance to get the tube in the best place.

My other concern with the foam knob insulation is all the knobs insulate the tube away from the concrete, in addition to the bottom of the pour performance hit. I've yet to see any of the knob board manufacturers have their outputs lab test.

Here are some test panels I built and datalogged

Derheatmeister

These are the type of Chairs that we use... they are made of Concrete so they are of the same material and they do not fold over or Break even with large Concrete contractors stomping on the Rebar they stay put..
Mark E. turned me on to these and they work wonderful !
The ony Issue i see with your Situation is that these may not elevate you tube half way into the
6" slab.
I think they are 1 1/2 high.
( 1 1/2 " Chair + 1/2" Rebar + 1/2 " Tubing = Approx 2 5/8" to the top of the tube.