In-slab radiant heating 1

[JLSE]

Hello again,
I am new to in-slab radiant heating... and have been researching it for a couple hours. Typically, I let the architect worry about it... but this architect is not doing his job....

I have some concerns which Id like to run by you all....
First, do these systems generally use water? What other substances are commonly used in California?

I am concerned about water leaking, and rusting....
I am considering using a topping slab for the heating coils, as a way to prevent rusting of structural slab steel ( slab on grade).
I am also considering putting the slab over sand over insulation over vapor barrier... as a way to get any water leakage away from the steel.

I see most details show the coils atop the steel... Im thinking it might be better to run them below the steel... to help with cracking on the top, and allow more cracking below.. letting the water out... as well as to protect the water lines from cutting wpj's, or anything in the future.

Second, what considerations have you made for the slab thickness.... for a slab on grade?

I am hoping someone can help me by pointing to a good (free) structural articles on this subject, or good (free) details.....

 

[DBronson]

JLSE:

Radiant systems nearly always use a water or water/glycol solution as the medium. Leakage in the system is pretty rare. Leaks are usually caused by contractors drilling into the floor or saw cutting the slab. You shouldn't need a topping slab. The tubing (nominally 3/4" OD) PEX is usually tied to the top of the steel mesh to hold it in place before the pour. The closer the tubing is to the upper surface the higher the heat output. Do not, under any circumstances put sand above the vapor barrier. Moisture will be trapped there causing endless problems for the Owner. Nominal slab thickness is 4" for residential and light commercial use. Two excellent sources of info are 1) Viega USA and 2) Building Science Corp. Viega's Concrete Systems Manual has most of the info you're looking for. (Note especially the expansion joint details) Building Science Corps' web site has several publications available on radiant systems from the ME's point of view.

There are hundreds of thousands of square feet of these systems installed every year - it's not that complicated.

Regards,
DB

 

[JLSE]

DB- Thank you. Those references had some good information.

It appears, my typical reinforcing spacing would not work well for securing the piping.... I typically use reinforcing bars, and from what I have read.... they need to secure the piping at 6" spacing on turns... so they could not use it.

I am considering using a structural mesh for reinforcing.... in the hopes that I can eliminate the need for the manuf. mesh.

But I would like to know what kind of steel mesh the manufacturer typically uses.... and if something like a structural mesh would/could be used to save money by eliminating the manufacturers mesh. So, if you could please answer these questions- How thick is the mesh the manufacturers seem to use to secure the pipe, whats the mesh spacing (is it around 6in x 6in), and can I provide a structural mesh for the manufactures use?

(added) - Also, Uponor shows an option to attach the piping directly to the insulation below..... that seems like a good option, addressing more of my previously stated concerns. Any redflags for that option?

 

[DBronson]

JLSE:

We've never used the mesh systems supplied by the tubing manufacturer. My understanding is that those systems are for larger spaces (>10,000SF). We've always secured the tubing to the 6 x 6 steel reinforcing mesh. Also, we've not used the system of anchoring the tubing to the insulation. As I mentioned in my post the heat output of the slab is reduced the deeper the tubing is buried in concrete. Since I don't know the heat required for your situation I can't say whether you in fact need the maximum output. I prefer the tubes in the center of the slab section surrounded by concrete. They're closer to the neutral axis as well. You could show both methods and allow the contractor to select the one they prefer.

Regards,

DB

NB: Be sure they follow the radiant system manual's initial start-up procedure for the heating system - if they increase the temperature too quickly they could cause cracking in the slab.

 

[bones206]

Here's a webinar from a few months back that has some good technical info.

https://www.youtube.com/watch?v=ekrWxFQmaN4